ApplyDisplayFormat is a procedure used to apply a new value in DisplayFormat to the Field used to get data for the column. Field must contain a valid TField instance, or no actions are performed in the method.

ApplyDisplayFormat ensures that the new value for DisplayFormat is properly applied to Fields using the TNumericField or TDateTimeField class types. ApplyDisplayFormat is used in the implementation of the LinkField method.

GetDataset is a TDataset function used to get the dataset which provides data for the column. GetDataset uses Grid (cast to a TCustomDBGrid instance) to access its DataLink and get the DataSet for the column definition. The return value is Nil if Grid has not been assigned for the column.

GetDisplayFormat is a String function used to get the value for the DisplayFormat property. The value in the member variable is returned when it is different than the stored value for DisplayFormat. Otherwise, the value from GetDefaultDisplayFormat is used as the return value.

Use DisplayFormat to read and write the value for the property.

GetField is a TField function used to get the value for the Field property. GetField ensures that Field has been assigned, and that FieldName has been set for the class instance. The LinkField method is called to find and store the TField instance used as the return value for the method. The return value is Nil if a Field with the name in FieldName cannot be found.

Use Field to read or write the value in the property.

GetIsDesignColumn is a Boolean function used to get the value for the IsDesignColumn property. The return value is True when DesignIndex contains a value in the range 0..9999.

The upper range for DesignIndex is a result of the value assigned in Create. The value 10000 is used in the property when Grid has not assigned for the collection, or Grid includes csLoading in its ComponentState property.

Use IsDesignColumn to read the value for the property.

IsDisplayFormatStored is a Boolean function used as the storage specifier for the DisplayFormat property. The return value is True if the member variable for the DisplayFormat property is different than the one used for the Field.

SetDisplayFormat is a procedure used to set the value in the DisplayFormat property. SetDisplayFormat compares the value stored in the member variable to the new value for the property. If they are different, the new value is stored and a flag is set to indicate that the display format has changed. SetDisplayFormat calls the ColumnChanged method to indicate that the column definition has been updated.

No actions are performed in the method when the DisplayFormat has not been changed.

Use DisplayFormat to read or write the value for the property.

SetField is a procedure used to set the value in the Field property. SetField compares the new value for the property to the value stored in the member variable. When they are different, the new value is stored in the member variable. If the new value is not Nil, its FieldName is updated as well. SetField calls the ColumnChanged method to indicate that the column definition has been updated.

No actions are performed in the method when the new Field value is the same as the value stored in the member variable .

Use Field to read or write the value for the property.

SetFieldName is a procedure used to set the value in the FieldName property. SetFieldName compares the new value to the value stored in the member variable for the property. No actions are performed in the method when they are the same.

SetFieldName stores the new value for the property in its member variable, and calls the LinkField method to find the Field with the specified name. DisplayFormat is updated when a matching Field is located in the dataset for the column.

CreateTitle is an overridden TGridColumnTitle function used to create the title used as a fixed caption for the column.

GetDefaultAlignment is an overridden TAlignment function that gets the default alignment for the Field in the column definition. GetDefaultAlignment gets the button style used by the default editor for Field. For checkbox and button-style editors, center alignment is used. Otherwise, the Alignment in Field is used. If Field has not been assigned, left alignment is used.

GetDefaultDisplayFormat is a String function used to get the default display format provided for the Field in a column definition. GetDefaultDisplayFormat uses the Field property to get its DisplayFormat for use as the return value in the method. The return value is a empty string ('') when Field has not been assigned for the column definition.

GetDefaultDisplayFormat is used in the implementation of the GetDisplayFormat method.

GetDefaultValueChecked is an overridden String function used to get the default value used for a Checkbox column in the Checked state. When Field has been assigned for the column, and the data type is ftBoolean, the return value is 'TRUE'. If Field has not been assigned, the return value is '1'.

GetDefaultValueUnchecked is an overridden String function used to get the default value used for a Checkbox column in the UnChecked state. When Field has been assigned for the column, and the data type is ftBoolean the return value is 'FALSE'. If Field has not been assigned, the return value is '0'.

GetDefaultVisible is an overridden Boolean function that indicates if the Field for the column is Visible. GetDefaultVisible uses Field to get its Visible property for use as the return value in the method. If Field has not been assigned in the column, the return value is True.

GetDisplayName is an overridden String function used to get the display name for the column. The display name is used at design-time to get the name for the collection item, and at run-time when a dataset for the column has not been assigned or opened.

The value in FieldName is used as the return value for the method, when it has been assigned in the column. Otherwise, the inherited GetDisplayName method is called to get the return value.

Use FieldName to set the name of the Field used for the column.

GetDefaultReadOnly is an overridden Boolean function which gets the default value for the ReadOnly property. GetDefaultReadOnly combines the ReadOnly values found in both the Grid and the Field for the dataset to derive the value for the method. The return value is True when Grid or Field is not assigned for the column.

GetDefaultWidth is an overridden Integer function used to get the effective width for the column. The return value is calculated using the Grid and its Canvas to find the space needed for the Field in the column. When the Grid has Options that include the value dgTitles, Title.Caption and Title.Font are included in the calculation. GetDefaultWidth calls the CalcColumnFieldWidth function to get the canvas width used as the return value.

The return value is -1 if the Grid has not been assigned for the column. The return value contains Grid.DefaultColWidth when Field has not been assigned in the column.

GetPickList is an overridden TStrings function which gets the values in the pick list for the column. GetPickList calls the inherited method, and provides support for Lookup Fields in the column definition.

When Field is assigned and contains a Lookup Field (fkLookup in its FieldKind property), values from the LookupList or the LookupDataset are included in the return value. When LookupDataset is used, the result includes values from the LookupResultField for each of the rows in the dataset.

IsAutomaticColumn is a read-only Boolean property that indicates if the column was automatically added to the collection at run-time. The value in IsAutomaticColumn is updated when TDBGrid.AddAutomaticColumns and TDBGridColumns.RemoveAutoColumns add or remove items in the collection.

Use IsDesignColumn to determine if the column was added at design-time. Use TDBGridColumns.HasAutomaticColumns to determine if any automatic columns are stored in the collection. Use TDBGrid.OptionsExtra to enable or disable automatically columns in a database grid control.

IsDesignColumn is a read-only Boolean property which indicates if the column was added at design-time. GetIsDesignColumn is the read access specifier for the IsDesignColumn property.

Use IsAutomaticColumn to determine if the column was added at run-time. Use TDBGridColumns.HasDesignColumns to determine if any design-time columns are stored in the collection.

LinkField is a procedure used to establish a link between the FieldName in the column and the Field in its Dataset. LinkField requires Grid to be assigned in order to access the DataLink and its Dataset. When Grid is unassigned, the value for Field is Nil. The DataLink in Grid must be Active to access the Fields in the dataset. When DataLink in not Active, the value in Field is Nil.

LinkField finds the Field in the linked dataset with the name specified in FieldName. The TField instance is stored in the Field property. LinkField calls the ApplyDisplayFormat method to update the DisplayFormat used for the column.

Create is the constructor for the TColumn instance. Create calls the inherited Create constructor and sets the DesignIndex used for the new entry in the TCollection. Create is called by the TCollection.Add method and should not be called directly under normal circumstances.

Assign is an overridden procedure which stores properties from Source in the current class instance. Assign calls the inherited Assign method. When Source is a TColumn class instance, the values for the following are stored in the current class instance:

• FieldName
• DisplayFormat
• ValueChecked
• ValueUnchecked

IsDefault is an overridden Boolean function that indicates if the column uses its default display format. The return value is True when the value in the DisplayFormat property has not been changed. IsDefault calls the inherited method to get the return value for the method.

Field is a TField property that provides access to the content and other attributes for the dataset Field represented by the column. GetField reads the value for the property. SetField writes the value for the property.

DesignIndex is a read-only Integer property that contains the order for the column in its collection at design-time. The value in DesignIndex is used primarily when TDBGridColumns.ResetColumnsOrder compares and sorts the items in its collection.

DisplayFormat is a String property which specifies a format string used for displaying the value of a Field with the name in FieldName. Use of DisplayFormat in TColumn is consistent with its use in TField (and decendants), but can assign a value that overrides the default display format for the Field.

GetDisplayFormat is the read access specifier for the property. SetDisplayFormat is the write access specifier for the property. Changing the value in DisplayFormat causes the ColumnChanged method to be called when the column definition has been updated.

FieldName is a String property which contains the name of the Field used to get data for the column. SetFieldName is the write access specifier for the property. Changing the value in FieldName causes LinkField to be called to find the Field with the specified name. The value in DisplayFormat is also modified when the property was has changed.

TDBGridColumns is a TGridColumns descendant which implements a collection for columns added to TDBGrid.

TDBGridColumns extends the ancestor class to include support for adding and removing automatic columns at run-time. Automatic columns are a feature in TDBGrid that, when enabled, ensures the collection has a column definition for each Field in the linked dataset for its grid control. Methods and Properties are provided to identify columns added at run-time, and to order entries in the collection by their design-time or run-time indices.

Items is the default property for the collection. TColumn is the class type used for Items added to the collection.

Use the Add method to create a new collection item in the Items property. Use LinkFields to update the association between an item in the collection and the TField used to access its data. Use ResetColumnsOrder to change the order of Items in the collection.

GetColumn is a TColumn function which gets the column at the specified position in the collection. GetColumn is the read access specifier for the Items property.

Use Items to read and write values in the collection.

SetColumn is a procedure which stores the column in Value at the specified position in the collection. SetColumn is the write access specifier for the Items property. SetColumn uses the Assign method to store the new Value in the collection.

Use Items to read and write values in the collection.

Update causes the TDBGrid control which owns the column collection to be redrawn. The value in Grid must be assigned, or no actions are performed in the method. In addition, the Grid control will not be updated if component streaming is active (csLoading in its ComponentState). Update calls TDBGrid.LayoutChanged to force the Grid control to be redrawn.

ColumnFromField returns the collection item for the specified Field. The return value is Nil when Field has not been assigned.

ColumnFromField iterates over the Items in the collection to locate the specified Field. The return value is Nil when Field cannot be located in the Items for the collection.

ColumnFromField is used in the TDBGrid.AddAutomaticColumns method.

Add creates and stores a new TColumn instance in the collection.

Add uses the Grid property (and the value in its GridStatus property) to determine whether the column is being explicitly added to the collection or added as a result of the automatic columns option in the grid. If the Grid contains the value gsAddingAutoColumns in its GridStatus property, existing automatic columns are left in the collection. Otherwise, RemoveAutoColumns is called prior to creating and storing the new TColumn instance.

Add calls the inherited Add method to create and store the new TColumn instance.

LinkFields is a procedure which associates column items to the corresponding Fields in the Dataset for the Grid. LinkFields uses Grid to call its BeginLayout and EndLayout methods prior to and immediately after linking the Items in the collection to fields in the Dataset. This forces the Grid control to be updated when the method has completed. LinkFields calls the TColumn.LinkField method for each of the Items in the collection.

Items is a TColumn property that provides indexed access to columns in the collection by their ordinal position (in the range 0..Count-1). Read and write access to columns in the Items property are cast to the TColumn class type used in the collection. Write access calls the Assign method in the TColumn instance stored at the specified position.

Items is the default property for the collection.

HasAutomaticColumns is a Boolean function that indicates if any items in the collection are an automatic column added at run-time. Automatic columns are a feature in TDBGrid enabled by adding the appropriate value to its OptionsExtra property. HasAutomaticColumns returns True if a TColumn instance in the Items property has its IsAutomaticColumn property set.

HasDesignColumns is a Boolean function that indicates if the collection contains any items explicitly added at design-time. HasDesignColumns returns True if Items contains a TColumn instance with its IsDesignColumn property set.

RemoveAutoColumns is a procedure used to remove any automatic columns in the collection. RemoveAutoColumns uses HasAutomaticColumns to determine if any action is required.

When HasAutomaticColumns returns True the Grid updates its GridStatus to include the value gsRemovingAutoColumns. RemoveAutoColumns calls the Delete method for any column having its IsAutomaticColumn property set to True. gsRemovingAutoColumns is removed from the GridStatus property in the Grid prior to exiting from the method.

Applications do not normally call the RemoveAutoColumns method. Use TDBGrid.OptionsExtra to disable the automatic columns feature in the grid control.

ResetColumnsOrder is a procedure used to arrange columns in the collection to the order specified in the ColumnOrder argument. ColumnOrder can contain the following values:

coDesignOrder

TColumn.DesignIndex (when available) is used to order collection items.

coFieldIndex

The index for the TColumn.Field (when available) is used to order collection items.

Otherwise, the index of the collection item is unchanged.

TCustomDBGrid is a TCustomGrid descendant and the base class for TDBGrid. TCustomDBGrid adds capabilities needed to implement a database-aware grid control. One key feature is the TComponentDataLink in DataLink used to coordinate access and event handlers between the grid control and its linked dataset. Another key feature is the use of the Options and OptionsExtra properties to enable/disable features or behaviors in the grid control.

TCustomDBGrid overrides certain features from the ancestor class to provide consistent use with Fields, Field kinds, and values in TDataset.

Applications should use the TDBGrid descendant which sets the scope of properties, methods, and event handlers to public or published.

GetCurrentField is a TField function used to get the value in the SelectedField property. GetCurrentField is the read access specifier for the SelectedField property. GetCurrentField calls GetFieldFromGridColumn to get the TField instance used as the value for the property.

Use SelectedField to read and write value for the property.

GetDataSource is a TDataSource function used to get the value for the DataSource property. GetDataSource is the read access specifier for the DataSource property. GetDataSource gets the DataSource property stored in DataLink as the return value for the method.

Use DataSource to read or write values in the property.

GetRecordCount is an Integer function used to get the number of records in the linked dataset. GetRecordCount uses the DataLink for the grid to get the RecordCount in its DataSet property. The record count is used as the return value for the method.

OnRecordChanged is a procedure which provides a default implementation for the OnRecordChanged event handler in TComponentDataLink. OnRecordChanged ensures that the grid control and the linked dataset are synchronized when refreshing the active record, selecting the current column, and re-enabling the edit control when EditMode is active.

OnDatasetChanged is a procedure which provides a default implementation for the OnDatasetChanged event handler in TComponentDataLink.

OnDatasetOpen provides a default implementation for the event handler in TComponentDataLink.

SetCurrentField is a procedure used to set the value in the SelectedField property. SetCurrentField is the write access specifier for the SelectedField property. SetCurrentField calls GetGridColumnFromField to ensure that the Field in AValue becomes the current column in the control. No actions are performed in the method when AValue contains the same value as the SelectedField property.

Use SelectedField to read or write the value for the property.

SetDataSource is a procedure used to set the value in the DataSource property. SetDataSource is the write access specifier for the DataSource property. SetDataSource stores the value in AValue in the DataSource property for DataLink, refreshes the column widths for the control, and calls UpdateActive.

Use DataSource to read or write the value in the property.

SetOptions is a procedure used to set the values in the Options property. SetOptions is the write access specifier for the Options property. SetOptions causes other aspects of the grid control to be updated to reflect changes in the property value. ChangedOptions is updated to reflect the enumeration values added or removed in the request. Some enumeration values force other features or behaviors to be disabled. For instance: row selection. Enabling row selection forces the options for editing, always displaying the editor, and row highlighting to be removed from the Options property. Finally, removing multi-selection from the Options property forces the SelectedRows and KeyBookmark properties to be cleared.

AValue is a TDBGridOptions argument that specifies features or behaviors that will be enabled or disabled in the grid control. Please note that these options are different than the TGridOption values used in the ancestor class.

As a result, SetOptions must translate any TDBGridOption values to their TGridOption equivalents and store them in the inherited Options property.

Options contains the following default values when the control is created:

• dgColumnResize
• dgColumnMove
• dgTitles
• dgIndicator
• dgRowLines
• dgColLines
• dgConfirmDelete
• dgCancelOnExit
• dgTabs
• dgEditing
• dgAlwaysShowSelection

See TDBGridOption for more information about values in the enumeration.

UpdateBufferCount is a procedure used to set the number of records buffered for the linked dataset. UpdateBufferCount requires that DataLink be marked as Active to set the buffer count. If DataLink.Active contains False, no actions are performed in the method.

UpdateBufferCount calls GetBufferCount to determine the number of rows that can be displayed in the control with the DefaultRowHeight. When Options includes the value dgTitles, the buffer count is decreased by 1 to account for the fixed title row. UpdateBufferCount stores the new value in the BufferCount property in DataLink.

UpdateBufferCount is called from the UpdateGridCounts method.

UpdateData is a virtual procedure used to perform pending updates for the selected cell to its Field in the grid Dataset. No action is performed if the selected cell has not been modified (or cannot be modified) or the Dataset is not in edit mode.

UpdateData ensures that the appropriate method is used to update Field data based on the TField.FieldKind for the modified column. Special handling is provided for lookup Fields to check the cached lookup list or to retrieve the lookup result using its key Fields.

UpdateData calls the EditingColumn method to disable the editing flag for the column prior to exit.

GetColumnCount is an Integer function used to get the number of visible columns or Fields for the grid control. GetColumnCount uses the Columns collection (when its has been Enabled) to get the value in VisibleCount. When Columns is not Enabled, and OptionsExtra has dgeAutoColumns enabled, the linked dataset is used to determine the number of Fields with their Visible flag set. The Dataset cannot be examined if the DataLink is not marked as Active.

GetColumnCount is called from the UpdateGridCounts method.

DefaultFieldColWidth is an Integer function used to get the default column width for the specified Field. When the specified Field contains Nil, the value from DefaultColWidth is used. Otherwise, the DisplayWidth property in the TField instance is used to get the Canvas.TextWidth for the DisplayName in the Field.

GetDsFieldFromGridColumn returns the identity of the dataset Field corresponding to the nominated grid column

GetFieldFromGridColumn obtain the Field either from a Db column or directly from dataset Fields.

GetGridColumnFromField - gets the corresponding grid column for the given Field.

FieldIndexFromGridColumn returns the index for the database Field corresponding to the stated grid column.

UpdateGridColumnSizes is a procedure used to update the sizes for automatically sized columns in the grid control. UpdateGridColumnSizes requires DefaultColWidths to be in use for the grid. No actions are performed in the method when DefaultColWidths contains False.

UpdateGridColumnSizes also requires the Options property to include the value dgAutoSizeColumns which enables the auto-sized columns feature. No actions are performed if the feature has not been enable for the grid control.

UpdateGridColumnSizes calls the UpdateAutoSizeColumns method to calculate the widths for the auto-sized columns.

DoLayoutChanged is a procedure used to update the grid and its scrollbars when the layout for the control has changed. No actions are performed in the method when the control is freed (contains csDestroying in its ComponentState).

DoLayoutChanged calls BeginUpdate to signal changes to the control, and UpdateGridCounts to determine the number of rows for the update. When UpdateGridCounts returns 0, the EmptyGrid method is called to clear the grid control. DoLayoutChanged calls EndUpdate to allow pending changes to be applied to the control. DoLayoutChanged calls UpdateScrollbarRange to update scrollbars (when used) for the control.

DoLayoutChanged is called from the EndLayout method.

RestoreEditor is a procedure used to re-enable the editor control in the grid after processing scrollbar messages. RestoreEditor is used when EditorMode contains True. No actions are performed in the method when EditorMode contains False. RestoreEditor toggles the value in EditorMode to force the editor to be refreshed and redrawn.

ISEOF is a Boolean function used to indicate if the linked dataset is positioned at the end-of-file. ISEOF uses the DataLink for the control to access its Active and Dataset properties. DataLink must be Active (contains True) to access its Dataset. The return value is True when the TDataset.EOF method returns True. The return value is False when DataLink is not Active, or TDataset.EOF returns False.

ISEOF is used in the KeyDown and MouseDown methods.

BeginLayout is a procedure which starts producing layout changes for the grid control. BeginLayout is used along with EndLayout to minimize the number of times layout changed notification events are triggered by the control. Layout changes occur when the control enables certain values in its Options property, when AutoAdjustColumn is called, and when the Columns collection links to Fields in the associated dataset.

BeginLayout increments the LayoutChangedCount variable that tracks the number of times the method is called for the control. EndLayout decrements that counter, and when it reaches 0 (zero), the DoLayoutChanged method is called.

CellClick calls the OnCellClick event handler if it is assigned for this particular cell.

CheckDisplayMemo is a Boolean function used to determine if the specified field is a Memo field that needs to be displayed in the grid control. The return value is True when the specified field has the value ftMemo in its DataType property, and the Options property has enabled the dgDisplayMemoText feature.

ColRowMoved is an overridden procedure used to signal event handlers when a row or a column is moved in the grid control. When IsColumn contains False, the OnRowMoved event handler is signalled (when assigned). When IsColumn contains True, the OnColumnMoved event handler is signalled (when assigned) if Columns have not been Enabled in the grid control. If Columns have been Enabled, the inherited ColRowMoved method is called.

CreateColumns is an overridden TGridColumns function used to create the Columns collection for the grid control. In TDBGrid, the Columns collection is implemented using the TDBGridColumns class type (a descendant of TGridColumns). CreateColumns creates an instance of TDBGridColumns which is used as the return value for the method.

DefaultDrawCell is a procedure that provides the default method for drawing a cell at the specified location using different cell types. DefaultDrawCell draws the background for the cell with the specified drawing state. For a cell which appears in a fixed row or column, the text for the cell is also drawn.

When the DataSet for the grid control has rows, the Field used for the specified column is retrieved and the cell is drawn in the manner needed for its column editor style. For checkbox columns, the DrawCheckBoxBitmaps is called. For columns with a button-style editor, the DrawButtonCell method is used. For Fields with a ftMemo data type, the CheckDisplayMemo method is called to determine whether the content in the memo or the DIsplayText for the column definition is drawn. Finally, the DrawCellText method is called to draw the specified cell using its state and value.

DoExit is an overridden procedure in TCustomDBGrid used to close the editor and the datalink for the control. A valid dataset must be assigned in the DataLink property and inserts must be cancellable for the dataset. The Options property must include the dgCancelOnExit enumeration value for the grid. If any of these conditions are not met, no actions are performed in the method on either the dataset or the Field editor.

DoExit calls the inherited method to perform any actions implemented in the ancestor class.

DrawFocusRect is an overridden procedure used to draw the current selection in the grid in a focused state.

The grid control must have focus before the current selection can be drawn. In addition the DataLink for the control must refer to an active dataset. DrawFocusRect uses the Options property to ensure that dgAlwaysShowSelection has been included for the control. Finally DefaultDrawing must be enabled to allow drawing of the focus rectangle using the rubberband style on the Canvas for the control.

If any of the previous conditions are not met, no actions are performed in the method.

DrawRow is an overridden procedure used to draw the specified row number in the grid control.

ARow contains the row number to be drawn and refers to an ordinal position relative to the FixedRows for the control. When ARows contains a value that would be in the FixedRows the state flags that track drawing an active record or multi-selection are reset. DrawRow also requires that DataLink refer to an active dataset. No actions are performed in the method if these conditions are not satisfied.

DrawRow sets the active record in DataLink for selected rows in the control and updates the DrawingActiveRecord and DrawingMultiSelRecord flags as needed. The Options property must include the value dgMultiSelect to enable drawing of multiple selections in the control.

DrawRow calls the inherited method to perform any actions implemented in the ancestor class.

DrawCell is used to render a cell at the specified coordinates with the specified drawing state.

EditingColumn is a procedure used to set or reset the column being edited in the control .

aCol indicates the ordinal column number and is stored internally for use in other methods of the control. Ok indicates that editing is active when set and causes the DataLink to set its Modified flag to true. When Ok contains False the internal column number is reset to its default value indicating that no column is currently being edited.

EditingColumn is used in the implementation of other methods in the grid control such as UpdateData, EditorCancelEditing, EditorIsReadOnly, and DoExit.

EditorCancelEditing is a procedure used to cancel pending changes and to halt the editing process.

EditorCancelEditing calls the EditingColumn method to disable the editor in the currently selected cell for the control. The EditorMode property is cleared when set, but is restored if the Options property includes the value dgAlwaysShowEditor.

EditorCancelEditing is used in the implementation of methods like DoOperation MoveSel and MouseDown.

EditorDoGetValue is an overridden procedure used to get the value used in the editor for the control. EditorDoGetValue calls the inherited EditorDoGetValue method. UpdateData is called to retrieve the value for the editor from its column in the underlying dataset.

EditorCanAcceptKey is an overridden Boolean function which determines if the cell editor can accept the character specified in ch. EditorCanAcceptKey requires that the linked dataset be active to access the SelectedField for the control. The Field cannot be an AutoIncrement, Lookup, Calculated, or Blob Field type. The return value is False if any of these conditions are not satisfied.

EditorCanAcceptKey calls the IsValidChar routine to determine if the UTF8-encoded value in ch can be applied to the dataset for the control.

EditorIsReadOnly is a Boolean function used to determine if the editor can be enabled for the selected cell in the control.

EditorIsReadOnly calls the inherited method to ensure that requirements from the ancestor class are respected. If the ancestor class returns True no actions are performed in the method.

EditorIsReadOnly locates the TField used to store data for the selected cell, and calls its CanModify method to determine if the Field can be modified. Additional logic is applied for lookup Fields; the TField.KeyFields for the Field are also examined to determine if any of them are marked as read-only.

EditorIsReadOnly ensures the dataset in DataLink is in edit mode. The GridStatus property is updated to include gsStartEditing prior to changing the dataset state, and removed from GridStatus after the dataset state has changed.

EditorIsReadOnly calls the EditingColumn method to synchronize the cell editor state to the value returned by the method.

EndLayout is a procedure used along with BeginLayout to minimize the number of times layout changed notification events are triggered by the control. Layout changes occur when the control enables certain values in its Options property when AutoAdjustColumn is called and when the Columns collection links to Fields in the associated dataset.

The grid maintains an internal counter that tracks the number of times BeginLayout has been called to start a layout change for the control. EndLayout decrements that counter, and when it reaches 0 (zero), the DoLayoutChanged method is called.

GetEditMask is an overridden String function used to get the EditMask for the TField that reads and writes data for specified Row and Column.

The linked dataset for the grid control must be active to access the Field definition at the specified column number. GetEditMask calls the GetFieldFromGridColumn method to get the TField instance with the EditMask for the column.

The return value can contain an empty string ('') is the dataset is not active, or a Field cannot be located for the specified column, or the EditMask has not been assigned in the Field definition.

GetEditMask signals the OnFieldEditMask event handler when it has been assigned for the control. Use OnFieldEditMask to return a user-specified value for the EditMask.

GetEditText is an overridden String function used to get the Text value for the Field at the specified Row and Column.

GetEditText requires that the linked dataset for the control be active to access its Field definitions. GetEditText calls the GetFieldFromGridColumn method to get the TField instance that provides the textual representation of the value for the Field. GetEditText calls the CheckDisplayMemo method to determine if a Field with the ftMemo data type displays its content or the string literal in its Text property '(Memo)'.

GridCanModify indicates if the DataLink is active, and allows editing.

HeaderClick - calls OnHeaderClick if assigned.

HeaderSized is an overridden procedure which updates the Columns for the control when a header cell is resized. If IsColumn contains False the resize operation was for the height of a header row and no action is performed in the method. When IsColumn contains True the request applies to the width of the column with the Field at the position specified in Index.

HeaderSized calls the ColumnIndexFromGridColumn method to determine the position in the Columns collection for the Field specified in Index. The width in Columns is updated with the corresponding value from ColWidths. HeaderSized sets the value in DefaultColWidths to False to indicate that custom column sizing has been applied to the control.

HeaderSized signals theOnColumnSized event handler when assigned for the control.

KeyDown ensures that keys which affect navigation and editing operations are handled in the grid control. KeyDown handles the following keys:

Tab

Advances to the next column when dgTabs is included in Options. Otherwise exits the control.

Shift + Tab

Moves to the previous column when dgTabs is included in Options. Otherwise exits the control.

Return

Enables the editor for the cell when dgEditing is included in Options. Otherwise advances to the next column.

Ctrl + Delete

Deletes the selected row when dgDisableDelete has not been included in Options. A confirmation dialog is displayed when dgConfirmDelete is included in Options.

Up

Moves to the previous row in the dataset. The currently selected column remains the same.

Down

Moves to the next row in the dataset. The currently selected column remains the same. Appends a new row when positioned at the end of the dataset and dgDiableInsert has not been included in Options.

Page Up

Moves towards the beginning of the dataset by the number of rows specified in VisibleRows.

Page Down

Moves towards the end of the dataset by the number of rows specified in VisibleRows.

Escape

Cancels an active editor for the selected cell. Clears pending modifications to the Field for the column.

Insert

Inserts a new row at the current row position when dgDisableInsert has not been included in Options. The actual position for the new row can change if the dataset has sorting or ordering capabilities.

Home

Changes the selected cell to first non-fixed column in the control. An active editor is removed.

Ctrl + Home

Moves to the first row in the dataset. An active editor is removed.

End

Changes the selected cell to the last visible column in the control. An active editor is removed.

Ctrl + End

Moves to the last row in the dataset. An active editor is removed.

Space

Toggles the value in a column which uses a checkbox editor.

Ctrl + Multiply (Num Pad *)

Toggles the selected state for the current row when dgMultiSelect is included in Options.

KeyDown reads and writes values in GridFlags as needed while handling cell editors and performing dataset navigation.

KeyDown calls the inherited KeyDown method to process keys not explicitly handled by the data-aware control.

KeyDown signals the OnKeyDown event handler when it has been assigned for the control.

LinkActive is a procedure which updates the control when the state of its DataLink is changing. Value contains False when the dataset for the DataLink will be closed. The state change causes updates to other control properties like SelectedRows, and the KeyBookmark which tracks the selected row in the linked dataset. LinkActive calls RemoveAutomaticColumns to remove automatic columns added to the control when the DataLink became active. The LayoutChanged method is called to refresh the control after updates to the Columns property.

No actions are performed in the method when Value contains True.

LayoutChanged is a virtual procedure used to link Columns to the Fields which read and write the values used in the control. LayoutChanged calls the TDBGridColumns.LinkFields method establish the column-to-field association. If Columns have not been explicitly defined the AddAutomaticColumns method is called to add a column for each Field in the linked dataset.

LayoutChanged calls the BeginLayout and EndLayout methods to minimize the number of times the OnLayoutChange event is signalled during updates to the control.

LayoutChanged performs no actions when ComponentState indicates the control is being destroyed (contains csDestroying).

Loaded performs the notification that signals component streaming has been completed at run-time. Loaded calls the LayoutChanged method to update the visual appearance of the control. Loaded calls the inherited Loaded method

MoveSelection causes the current selection in the control to be changed. MoveSelection calls the inherited MoveSelection method. If the selection change causes a different column to become active, the OnColEnter event handler is signalled (when assigned). MoveSelection calls the UpdateActive method to ensure that the correct row and/or column are drawn in the control.

MouseDown handles mouse button clicks (when allowed) in the control. MouseDown ensures that the specified Button and State are correctly applied to the control similar to the processing provided in KeyDown method. MouseDown translates screen coordinates into the row and column numbers used in the control and performs actions needed for focus selection editing or navigation.

MouseDown signals the OnMouseDown event handler when assigned in the class instance.

PrepareCanvas prepares the Canvas used to render the cell at the specified position with the drawing state in aState. PrepareCanvas calls the inherited PrepareCanvas method and sets the brush color in the Canvas to the value need for fixed or focus/selected columns.

SelectEditor is a procedure used to get the editor used for the SelectedField in the control. SelectEditor requires an active dataset in DataLink to access properties and methods in SelectedField. SelectEditor uses SelectedField to get the maximum length of the Field in the dataset and stores the value in the Editor for the control.

SelectEditor calls the Inherited SelectEditor method to initialize the class used in the Editor property. SelectEditor signals the OnSelectEditor event handler (when assigned) to get a custom value for the Editor property. Please note that Editor is set to Nil if the OnSelectEditor event handler is not assigned for the control.

SetEditText sets the textual value for the editor in the specified cell.

UpdateActive forces the control to be redrawn when the active row in the linked dataset is changed. UpdateActive requires an active dataset in DataLink with a selected record. No actions are performed in the method when the dataset is closed or contains no rows. UpdateActive calls InvalidateCell when the selected row in the control has changed. InvaidateRow is called to update the selected row in the control.

UpdateGridCounts is an Integer function which gets the total number of visible columns (or fields) in the grid control.

UpdateGridCounts calls GetColumnCount to get the number of entries in the Columns collection. When Columns have been defined, and DataLink is Active, the RecCount and RowCount variables are updated. The UpdateGridColumnSizes method is used to adjust the sizes for the columns. If the linked dataset is Active, and a Row is Selected, the AdjustEditorBounds method is called.

Columns is a TDBGridColumns property that provides access to columns defined for the database grid control. Items in the Columns collection are represented as TColumn instances and can be explicitly created in the IDE at design-time, or automatically added when the OptionsExtra property includes the value dgeAutoColumns.

DataSource is a TDataSource property which provides access to the DataSet displayed in the database grid control. Read and write access to the property are redirected to the DataLink property.

Reading the value for DataSource returns the value stored in the TComponentDataLink instance.

Writing the value for DataSource sets the value in the TComponentDataLink instance (when they are not the same). Write access to DataSource also resets the width of columns in the grid by calling RenewColWidths. UpdateActive is called to redraw the grid control after changes to the DataSource and Columns properties.

Options is a TDBGridOptions property that specifies features or behaviors that can be enabled or disabled by values stored in the property. Please note that these options are different than the TGridOption values used in the ancestor class. Options can contain zero (0) or more values from the TDBGridOption enumeration.

Options contains the following default values when the control is created:

• dgColumnResize
• dgColumnMove
• dgTitles
• dgIndicator
• dgRowLines
• dgColLines
• dgConfirmDelete
• dgCancelOnExit
• dgTabs
• dgEditing
• dgAlwaysShowSelection

See TDBGridOption for more information about values in the enumeration and their meanings.

Changing value(s) in Options causes other aspects of the grid control to be updated to reflect change(s) to the property. ChangedOptions is updated to reflect the enumeration values added or removed in the request. Some enumeration values force other features or behaviors to be disabled. For instance: row selection. Enabling row selection forces the options for editing, always displaying the editor, and row highlighting to be removed from the Options property. Finally, removing multi-selection from the Options property forces the SelectedRows and KeyBookmark properties to be cleared.

The TDBGridOption values stored in Options are different than the TGridOption values used in the ancestor class. As a result, SetOptions (the write access specifier) must translate any TDBGridOption values to their TGridOption equivalents and store them in the inherited Options property. Welcome to the dark world of inheritance in visual controls. It's tedious... just look at the code.

ReadOnly is a Boolean property that indicates if modifications are allowed in the grid control. Please note that ReadOnly applies to the visual grid control only. It does not take into account whether Fields in Columns or the DataSet in DataSource allows modifications.

OnCellClick is a TDBGridClickEvent property that contains the event handler signalled when a mouse button is clicked in a cell for the grid control. Assign a procedure to the OnCellClick property to respond to mouse click messages in a column for the grid control.

OnCellClick is used the implementation of the CellClick method.

OnColEnter is a TNotifyEvent property that implements the event handler signalled when the mouse enters a column for the grid control. OnColEnter is also signalled when the grid control gains focus. Assign a procedure to the property to allow responding to the notification event.

OnColEnter is triggered from the MoveSelection method.

OnColExit is a TNotifyEvent property that implements the event handler signalled when the mouse exits a column in the grid control. OnColExit is also signalled when the grid control loses focus. Assign a procedure to the property to allow responding to the notification event.

OnColExit is triggered from the BeforeMoveSelection method.

OnColumnMoved is a TMovedEvent property that implements an event handler signalled when the order of a column in the grid control is changed. Assign a procedure to the event handler to respond to the event notification. OnColumnMoved is triggered from the ColRowMoved method after the new column ordering has been applied.

Use OnRowMoved to responding to row ordering notification events.

OnDrawColumnTitle is a TDrawColumnCellEvent property that implements the event handler signalled when a cell title in the control needs to be drawn. Assign a procedure to the event handler to perform drawing needed for the cell title using the arguments to the routine.

OnDrawColumnCell is a TDrawColumnCellEvent property that implements the event handler signalled when a cell in the control needs to be drawn. Assign a procedure to the event handler to perform drawing needed for the cell using the arguments to the routine.

OnDrawColumnCell is triggered from the DrawCell method after the Canvas is prepared and any fixed cell or DefaultDrawing is performed. Please note that OnDrawColumnCell is not performed at design-time, or for fixed rows in the grid control.

OnFieldEditMask is a TGetDbEditMaskEvent property that implements the event handler signalled to get the edit mask used for a Field in the grid control. OnFieldEditMask allows overriding the edit mask assigned to a Field in the Columns property, or assigning an edit mask for Fields that do not already have one. Assign a procedure to the event handler to respond to the event notification.

OnFieldEditMask is triggered from the GetEditMask method when the DataSet in DataLink is active.

OnTitleClick is a TDBGridClickEvent property that implements the event handler signalled when a mouse click occurs in the fixed title cell for a column. Use OnTitleClick to perform actions required when the title cell for a column is clicked. Assign a procedure to the event handler to respond to the event notification.

OnTitleClick is triggered from the DoHeaderClick method.

Create is the constructor for the TCustomDBGrid instance. Create calls the inherited Create method, and allocates resources for properties in the class instance. Create sets the default event handlers used in DataLink to the corresponding procedures in the class:

• OnDataSetChanged
• OnDataSetClose
• OnDataSetOpen
• OnDataSetScrolled
• OnEditingChanged
• OnFocusControl
• OnInvalidDataset
• OnInvalidDataSource
• OnLayoutChanged
• OnRecordChanged
• OnUpdateData

Create calls RenewColWidths to set columns to their default widths and to disable column auto-sizing.

Create sets the values in the Options property to establish the baseline features and behavior enabled for the grid control, including:

• dgColumnResize
• dgColumnMove
• dgTitles
• dgIndicator
• dgRowLines
• dgColLines
• dgConfirmDelete
• dgCancelOnExit
• dgTabs
• dgEditing
• dgAlwaysShowSelection

See the Options property and TDBGridOption type for more information on values in the enumeration.

Values in the Options property from the ancestor class are also updated. They use the set of enumeration values in TGridOption, and are updated to include values which correspond to the TDBGridOption values used in the database grid control.

Create sets the default values in the ExtraOptions property to the following:

• dgeAutoColumns
• dgeCheckboxColumn

The value of the AutoAdvance property is set to aaRightDown, indicating the cell navigation is from left-to-right and then top-to-bottom in the grid control.

Create sets the value in ScrollBars to ssBoth indicating that both horizontal and vertical scroll bars are needed, and sets AllowOutboundEvents to False to prevent forwarding of event notifications to the ancestor class.

DefaultDrawColumnCell is the default method used for drawing cells in a column. DefaultDrawColumnCell uses the specified column to get the Field and the editor style needed to render the cell.

Checkbox columns are drawn by calling the DrawCheckBoxBitmaps method. Other editor styles use the DisplayText for the TField as the value drawn using the DrawCellText method. Please note that Fields with a data type of ftBlob are always rendered as the string literal '(blob)'.

Use the OnDrawColumnCell event handler to render a cell when DefaultDrawing is not enabled for the grid control.

Destroy is the overridden destructor in TCustomDbGrid. Destroy frees any bookmarks stored in the SelectedRows property. Destroys ensures that event handlers assigned to its DataLink property are removed prior to freeing resources allocated to the property.

Destroy calls the inherited Destroy method.

SelectedField is a TField property with the Field used to read and write data for the selected column in the grid control. SelectedField is updated when column navigation occurs in the control.

GetCurrentField is the read access specifier for the property, and returns the TField instance derived by GetFieldFromGridColumn for the selected column. SetCurrentField is the write access specifier for the property, and stores the new Field value as the selected column. No action is performed if the new Field value is the same as the current value for the property.

SelectedField is used in the implementation of various method in the control, such as: KeyDown, SelectEditor, UpdateData, and SwapCheckBox.

Use SelectedColumn to get the TColumn instance for the currently selected cell in the grid control.