delphi - 我如何判断 Delphi 控件当前是否可见？

Question

我需要一种方法来让自定义控件(从 TCustomControl 派生)来判断它当前是否可见。我不是在谈论 .Visible 属性；我的意思是它目前是否实际显示在屏幕上。有谁知道该怎么做吗？

Answer 1

几年前，我在表单方面遇到了同样的问题:我正在寻找一种方法来确定表单是否实际上对用户可见(即使只是部分可见)。
特别是当它应该是可见的并且 Showing 为 True 但窗口实际上完全位于另一个窗口后面时。
这是代码，它可以适用于 WinControl...

{----------------------------------------------------------}
function IsMyFormCovered(const MyForm: TForm): Boolean;
var
   MyRect: TRect;
   MyRgn, TempRgn: HRGN;
   RType: Integer;
   hw: HWND;
begin
  MyRect := MyForm.BoundsRect;            // screen coordinates
  MyRgn := CreateRectRgnIndirect(MyRect); // MyForm not overlapped region
  hw := GetTopWindow(0);                  // currently examined topwindow
  RType := SIMPLEREGION;                  // MyRgn type

// From topmost window downto MyForm, build the not overlapped portion of MyForm
  while (hw<>0) and (hw <> MyForm.handle) and (RType <> NULLREGION) do
  begin
    // nothing to do if hidden window
    if IsWindowVisible(hw) then
    begin
      GetWindowRect(hw, MyRect);
      TempRgn := CreateRectRgnIndirect(MyRect);// currently examined window region
      RType := CombineRgn(MyRgn, MyRgn, TempRgn, RGN_DIFF); // diff intersect
      DeleteObject( TempRgn );
    end; {if}
    if RType <> NULLREGION then // there's a remaining portion
      hw := GetNextWindow(hw, GW_HWNDNEXT);
  end; {while}

  DeleteObject(MyRgn);
  Result := RType = NULLREGION;
end;

function IsMyFormVisible(const MyForm : TForm): Boolean;
begin
  Result:= MyForm.visible and
           isWindowVisible(MyForm.Handle) and
           not IsMyFormCovered(MyForm);
end;