如何判断Delphi控件当前是否可见？

Question

我需要一种方法来自定义控件(TCustomControl的后代)来判断它当前是否可见.我不是在谈论.Visible属性; 我的意思是它是否实际上正在屏幕上显示.有谁知道如何做到这一点？

Answer 1

几年前,我对表单遇到了同样的问题:我正在寻找一种方法来确定表单是否实际可见(甚至只是部分)给用户.
特别是当它应该是可见的并且显示是真的但是窗口实际上完全落后于另一个.
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;