TTaskDialog: implement property Handle. Makes it possible to send messages to the dialog.

This is needed to implement e.g. progressbar and can be used to update on-the-fly the contents of the dialog.

lcl/dialogs.pp

@@ -652,6 +652,7 @@ type
     FFlags: TTaskDialogFlags;
     FFooterIcon: TTaskDialogIcon;
     FFooterText: TTranslateString;
+    FHandle: THandle;
     FMainIcon: TTaskDialogIcon;
     FModalResult: TModalResult;
     FOnDialogConstructed: TNotifyEvent;
@@ -703,6 +704,8 @@ type
     //which might be implemented in a derived class, but the event handler must be in base class for Delphi compatibility.
     procedure DoOnNavigated; dynamic;
 
+    procedure InternalSetDialogHandle(AHandle: THandle);  //only to be called from the dialog window
+
     procedure SetRadioButtonFromRadioIndex(AIndex: Integer);
   public
     constructor Create(AOwner: TComponent); override;
@@ -724,6 +727,7 @@ type
     property FooterIcon: TTaskDialogIcon read FFooterIcon write FFooterIcon default tdiNone;
     property FooterText: TTranslateString read FFooterText write FFooterText;
     property MainIcon: TTaskDialogIcon read FMainIcon write FMainIcon default tdiInformation;
+    property Handle: THandle read FHandle; //Handle to the dialog window
     property ModalResult: TModalResult read FModalResult write FModalResult;
     property QueryChoices: TStrings read FQueryChoices write SetQueryChoices;
     property QueryItemIndex: Integer read FQueryItemIndex write FQueryItemIndex;

lcl/include/taskdialog.inc

@@ -98,6 +98,8 @@ begin
 
   FCustomFooterIcon := TIcon.Create;
   FCustomMainIcon := TIcon.Create;
+
+  FHandle := 0;
 end;
 
 function TCustomTaskDialog.ButtonIDToModalResult(const AButtonID: Integer
@@ -244,6 +246,11 @@ begin
     FOnNavigated(Self);
 end;
 
+procedure TCustomTaskDialog.InternalSetDialogHandle(AHandle: THandle);
+begin
+  FHandle := AHandle;
+end;
+
 procedure TCustomTaskDialog.SetRadioButtonFromRadioIndex(AIndex: Integer);
 begin
   if (AIndex >= TaskDialogFirstRadioButtonIndex) and (AIndex-TaskDialogFirstRadioButtonIndex < RadioButtons.Count) then

lcl/interfaces/win32/win32wsdialogs.pp

@@ -1663,6 +1663,10 @@ begin
       Assert((Dlg is TCustomTaskDialog),'TaskDialogCallbackProc: dwRefData is NOT a TCustomTaskDialog');
       {$PUSH}
       {$ObjectChecks OFF}
+      //testing shows that hwnd is the same in all notifications
+      //and since TDN_DIALOG_CONSTRUCTED comes first, just set it here
+      //so any OnTaskDialogxxx event will have access to the correct handle.
+      TTaskDialogAccess(Dlg).InternalSetDialogHandle(hwnd);
       TTaskDialogAccess(Dlg).DoOnDialogConstructed;
       {$POP}
     end;

lcl/taskdlgemulation.pp

@@ -960,6 +960,7 @@ procedure TLCLTaskDialog.DoDialogConstructed;
 begin
   {$PUSH}
   {$ObjectChecks OFF}
+  {%H-}TTaskDialogAccess(FDlg).InternalSetDialogHandle(Handle);
   {%H-}TTaskDialogAccess(FDlg).DoOnDialogConstructed;
   {$POP}
 end;