check box in TListView header column - How to prevent it from stealing focus?
checkbox, delphi, delphi-5, listview
Solution
Do not process the `WM_COMMAND` message for a `BN_CLICKED` notification, the behavior you want about having a click while pressing the button and then draggging outside after the click won't work otherwise. A click consists of pressing and releasing the button on the control.
Instead you can look for if the mouse is clicked inside the control and then switch the checked state if it is. You can eat the mouse message after that, so the control won't receive the focus. But this should be checked in the window procedure of the checkbox, not the list view. Modified code:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ComCtrls, StdCtrls;
type
TForm1 = class(TForm)
ListView1: TListView;
CheckBox1: TCheckBox;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
FListHeaderChk: TCheckBox;
FSaveListHeaderChkWndProc: TWndMethod;
FListHeaderWnd: HWND;
procedure ListHeaderChkWndProc(var Msg: TMessage);
end;
var
Form1: TForm1;
implementation
uses
commctrl;
{$R *.dfm}
function GetCheckSize: TPoint; // from checklst.pas
begin
with TBitmap.Create do
try
Handle := LoadBitmap(0, PChar(OBM_CHECKBOXES));
Result.X := Width div 4;
Result.Y := Height div 3;
finally
Free;
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
CheckSize: TPoint;
HeaderSize: TRect;
begin
ListView1.HandleNeeded;
FListHeaderWnd := ListView_GetHeader(ListView1.Handle);
FListHeaderChk := TCheckBox.Create(nil);
CheckSize := GetCheckSize;
FListHeaderChk.Height := CheckSize.X;
FListHeaderChk.Width := CheckSize.Y;
ShowWindow(ListView1.Handle, SW_SHOWNORMAL);
windows.GetClientRect(FListHeaderWnd, HeaderSize);
FListHeaderChk.Top := (HeaderSize.Bottom - FListHeaderChk.Height) div 2;
FListHeaderChk.Left := FListHeaderChk.Top;
FListHeaderChk.Parent := Self;
FListHeaderChk.TabStop := False;
windows.SetParent(FListHeaderChk.Handle, FListHeaderWnd);
FSaveListHeaderChkWndProc := FListHeaderChk.WindowProc;
FListHeaderChk.WindowProc := ListHeaderChkWndProc;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
FListHeaderChk.Free;
end;
procedure TForm1.ListHeaderChkWndProc(var Msg: TMessage);
begin
if (Msg.Msg = WM_MOUSEACTIVATE) and (Msg.LParamLo = HTCLIENT) then begin
Msg.Result := MA_NOACTIVATEANDEAT;
FListHeaderChk.Checked := not FListHeaderChk.Checked;
Exit;
end;
FSaveListHeaderChkWndProc(Msg);
end;
end.
Problem
This is related to the question How to show a check box in TListView header column?. I want to use the code from this answer by `@Sertac Akyuz`. (I need this to work in WinXP also) But I want to make the header CheckBox to not steal focus from the ListView or other active controls. A fast workaround is to set the focus always to the ListView in the `ListHeaderWndProc`: ``` ... FListHeaderChk.Checked := not FListHeaderChk.Checked; ListView1.SetFocus; // code that checks/clears all items ``` But this is kinda ugly. Because the CheckBox is first focused and then the focus goes back to the ListView. also If I click the CheckBox and drag the mouse outside the CheckBox it fails to receive the `BN_CLICKED` message. I have also tried: ``` TCheckBox = class(StdCtrls.TCheckBox) private procedure WMMouseActivate(var Message: TWMMouseActivate); message WM_MOUSEACTIVATE; protected procedure CreateParams(var Params: TCreateParams); override; public procedure DefaultHandler(var Message); override; end; procedure TCheckBox.WMMouseActivate(var Message: TWMMouseActivate); begin Message.Result := MA_NOACTIVATE; // no effect! end; procedure TCheckBox.CreateParams(var Params: TCreateParams); const WS_EX_NOACTIVATE = $08000000; begin inherited; Params.ExStyle := Params.ExStyle or WS_EX_NOACTIVATE; // no effect! end; procedure TCheckBox.DefaultHandler(var Message); begin case TMessage(Message).Msg of WM_SETFOCUS: begin if IsWindow(TWMSetFocus(Message).FocusedWnd) then begin TMessage(Message).Result := 1; // ??? // inherited // ??? Windows.SetFocus(TWMSetFocus(Message).FocusedWnd); Exit; // Checkbox fails to receive `BN_CLICKED` message end; end; end; inherited; end; ``` Nothing works. What am I missing?