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POSynchronized Scrolling Components Delphi
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copied!<p>I am trying to synchronize the scrolling of two TDBGrid components in a VCL Forms application, I am having difficulties intercepting the WndProc of each grid component without some stack issues. I have tried sending WM_VSCROLL messages under scrolling events but this still results in the incorrect operation. It needs to work for clicking the scrollbar, as well as highlighting a cell, or an up or down mouse button. The whole idea is to have two grids next to each other displaying a sort of matching dialog.</p> <p><strong><em>Tried</em></strong></p> <pre><code>SendMessage( gridX.Handle, WM_VSCROLL, SB_LINEDOWN, 0 ); </code></pre> <p><strong><em>Also</em></strong></p> <pre><code>procedure TForm1.GridXCustomWndProc( var Msg: TMessage ); begin Msg.Result := CallWindowProc( POldWndProc, gridX.Handle, Msg.Msg, Msg.wParam, Msg.lParam ); if ( Msg.Msg = WM_VSCROLL ) then begin gridY.SetActiveRow( gridX.GetActiveRow ); gridY.Perform( Msg.Msg, Msg.wParam, Msg.lParam ); SetScrollPos( gridY.Handle, SB_VERT, HIWORD( Msg.wParam ), True ); end; end; </code></pre> <p><strong><em>And</em></strong></p> <pre><code>procedure TForm1.GridxCustomWndProc( var Msg: TMessage ); begin if ( Msg.Msg = WM_VSCROLL ) then begin gridY.SetActiveRow( gridX.GetActiveRow ); gridY.Perform( Msg.Msg, Msg.wParam, Msg.lParam ); SetScrollPos( gridY.Handle, SB_VERT, HIWORD( Msg.wParam ), True ); end; inherited WndProc( Msg ); end; </code></pre> <p>The First is only a temporary solution, the second results in invalid memory reads, and the third results in a stack overflow. So none of these solutions seems to work for me. I'd love some input on how to accomplish this task! Thanks in advance.</p> <h1>UPDATE: Solution</h1> <pre><code> private [...] GridXWndProc, GridXSaveWndProc: Pointer; GridYWndProc, GridYSaveWndProc: Pointer; procedure GridXCustomWndProc( var Msg: TMessage ); procedure GridYCustomWndProc( var Msg: TMessage ); procedure TForm1.FormCreate(Sender: TObject); begin GridXWndProc := classes.MakeObjectInstance( GridXCustomWndProc ); GridXSaveWndProc := Pointer( GetWindowLong( GridX.Handle, GWL_WNDPROC ) ); SetWindowLong( GridX.Handle, GWL_WNDPROC, LongInt( GridXWndProc ) ); GridYWndProc := classes.MakeObjectInstance( GridYCustomWndProc ); GridYSaveWndProc := Pointer( GetWindowLong( GridY.Handle, GWL_WNDPROC ) ); SetWindowLong( GridY.Handle, GWL_WNDPROC, LongInt( GridYWndProc ) ); end; procedure TForm1.GridXCustomWndProc( var Msg: TMessage ); begin Msg.Result := CallWindowProc( GridXSaveWndProc, GridX.Handle, Msg.Msg, Msg.WParam, Msg.LParam ); case Msg.Msg of WM_KEYDOWN: begin case TWMKey( Msg ).CharCode of VK_UP, VK_DOWN, VK_PRIOR, VK_NEXT: GridY.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); end; end; WM_VSCROLL: GridY.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); WM_HSCROLL: GridY.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); WM_MOUSEWHEEL: begin ActiveControl := GridY; GridY.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); end; WM_DESTROY: begin SetWindowLong( GridX.Handle, GWL_WNDPROC, Longint( GridXSaveWndProc ) ); Classes.FreeObjectInstance( GridXWndProc ); end; end; end; procedure TForm1.GridXMouseDown( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer ); begin GridY.SetActiveRow( GridX.GetActiveRow ); end; procedure TForm1.GridYCustomWndProc( var Msg: TMessage ); begin Msg.Result := CallWindowProc( GridYSaveWndProc, GridY.Handle, Msg.Msg, Msg.WParam, Msg.LParam ); case Msg.Msg of WM_KEYDOWN: begin case TWMKey( Msg ).CharCode of VK_UP, VK_DOWN, VK_PRIOR, VK_NEXT: GridX.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); end; end; WM_VSCROLL: GridX.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); WM_HSCROLL: GridX.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); WM_MOUSEWHEEL: begin ActiveControl := GridX; GridX.Perform( Msg.Msg, Msg.WParam, Msg.LParam ); end; WM_DESTROY: begin SetWindowLong( GridY.Handle, GWL_WNDPROC, Longint( GridYSaveWndProc ) ); Classes.FreeObjectInstance( GridYWndProc ); end; end; end; procedure TForm1.GridYMouseDown( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer ); begin GridX.SetActiveRow( GridY.GetActiveRow ); end; </code></pre> <p>Thanks to - Sertac Akyuz for the solution. When integrated into a VCL forms application using grids, they will mimmic each other in scrolling, and highlighting the selected record.</p>

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