Merge branch 'lvonchanging'

lcl/comctrls.pp

@@ -1289,6 +1289,8 @@ type
 
   TLVChangeEvent = procedure(Sender: TObject; Item: TListItem;
                              Change: TItemChange) of object;
+  TLVChangingEvent = procedure (Sender: TObject; Item: TListItem;
+                                Change: TItemChange; var AllowChange: Boolean) of object;
 
   TLVDataFindEvent = procedure(Sender: TObject; AFind: TItemFind;
     const AFindString: string; const AFindPosition: TPoint; AFindData: Pointer;
@@ -1429,6 +1431,7 @@ type
     // FLastVertScrollInfo: TScrollInfo;
     FUpdateCount: integer;
     FOnChange: TLVChangeEvent;
+    FOnChanging: TLVChangingEvent;
     FOnColumnClick: TLVColumnClickEvent;
     FOnCompare: TLVCompareEvent;
     FOnData: TLVDataEvent;
@@ -1522,6 +1525,7 @@ type
     function CreateListItems: TListItems; virtual;
     function CanEdit(Item: TListItem): Boolean; virtual;
     procedure Change(AItem: TListItem; AChange: Integer); virtual;
+    function CanChange(AItem: TListItem; AChange: Integer): Boolean;
     procedure ColClick(AColumn: TListColumn); virtual;
 
     procedure Delete(AItem : TListItem); virtual;
@@ -1593,6 +1597,7 @@ type
     property ToolTips: Boolean index Ord(lvpToolTips) read GetProperty write SetProperty default True;
     property ViewStyle: TViewStyle read FViewStyle write SetViewStyle default vsList;
     property OnChange: TLVChangeEvent read FOnChange write FOnChange;
+    property OnChanging: TLVChangingEvent read FOnChanging write FOnChanging;
     property OnColumnClick: TLVColumnClickEvent read FOnColumnClick write FOnColumnClick;
     property OnCompare: TLVCompareEvent read FOnCompare write FOnCompare;
     property OnCreateItemClass: TLVCreateItemClassEvent read FOnCreateItemClass write FOnCreateItemClass;
@@ -1741,6 +1746,7 @@ type
     property OnAdvancedCustomDrawItem;
     property OnAdvancedCustomDrawSubItem;
     property OnChange;
+    property OnChanging;
     property OnClick;
     property OnColumnClick;
     property OnCompare;

lcl/include/customlistview.inc

@@ -205,6 +205,22 @@ begin
   then FOnChange(Self, AItem, ItemChange);
 end;
 
+function TCustomListView.CanChange(AItem: TListItem; AChange: Integer): Boolean;
+var
+  ItemChange: TItemChange;
+begin
+  Result := True;
+  case AChange of
+    LVIF_TEXT: ItemChange := ctText;
+    LVIF_IMAGE: ItemChange := ctImage;
+    LVIF_STATE: ItemChange := ctState;
+  else
+    Exit;
+  end;
+  if Assigned(FOnChanging) then
+    FOnChanging(Self, AItem, ItemChange, Result);
+end;
+
 {------------------------------------------------------------------------------}
 {   TCustomListView ColClick                                                   }
 {------------------------------------------------------------------------------}
@@ -261,6 +277,7 @@ var
   Item: TListItem;
   n: Integer;
   oldSelected: TListItem;
+  AllowChange: Boolean;
 begin
   nm := PNMListView(AMessage.NMHdr);
   // ignore any notifications while initializing items
@@ -295,6 +312,7 @@ begin
 //    LVN_GETDISPINFO:
 //    LVN_ODCACHEHINT:
 //    LVN_ODFINDITEM:     implemented in win32 widgetset
+//    LVN_ITEMCHANGING:   implemented in win32 widgetset
 //    LVN_ODSTATECHANGED:
 //    LVN_BEGINLABELEDIT: implemented via TCustomListViewEditor
 //    LVN_ENDLABELEDIT:   implemented via TCustomListViewEditor
@@ -308,10 +326,14 @@ begin
       // see delete
       // besides... who's inserting items
     end;
+
     LVN_ITEMCHANGING: begin
-      //Check
+      //Currently implemented in win32 widgeset only
+      //in response CanChange should be called and the result of that function most likely
+      //should be handled at WS level (if at all possible for non-windows)
     end;
-    LVN_ITEMCHANGED:
+
+LVN_ITEMCHANGED:
     begin
       if nm^.iItem < 0 then
         Item := nil

lcl/interfaces/win32/win32wscustomlistview.inc

@@ -296,6 +296,32 @@ var
     end;
   end;
 
+  procedure HandleListViewChanging(ALV: TCustomListViewAccess);
+  var
+    nm: PNMListView;
+    Item: TListItem;
+  begin
+    //debugln(['HandleListChanging: HandleAllocated=',ALV.HandleAllocated,', (wcfInitializing in FWinControlFlags)=',Dbgs(wcfInitializing in ALV.FWinControlFlags)]);
+    if (wcfInitializing in ALV.FWinControlFlags) then Exit;
+    nm := PNMListView(NMHdr);
+    if nm^.iItem < 0 then
+      Item := nil
+    else
+      Item := ALV.Items[nm^.iItem];
+
+    if Assigned(Item) then
+    begin
+      //https://learn.microsoft.com/en-us/windows/win32/controls/lvn-itemchanging
+      //Returns TRUE to prevent the change, or FALSE to allow the change
+      //So the opposite of the result of CanChange function
+      if ALV.CanChange(Item, nm^.uChanged) then
+        MsgResult := 0 //Ord(BOOL(False))
+      else
+        MsgResult := 1; //Ord(BOOL(True))
+    end;
+    WinProcess := False;
+  end;
+
   procedure HandleListViewOwnerDataHint(ALV: TCustomListViewAccess);
   var
     DataHintInfo: PNMLVCACHEHINT;
@@ -323,6 +349,8 @@ begin
           end;
         LVN_ODFINDITEM:
           HandleListViewFindItem(TCustomListViewAccess(AWinControl));
+        LVN_ITEMCHANGING:
+          HandleListViewChanging(TCustomListViewAccess(AWinControl));
         LVN_ODCACHEHINT:
           HandleListViewOwnerDataHint(TCustomListViewAccess(AWinControl));
       end;