delphi - 如何在单击 TButton 时显示 TPopupMenu？

Question

我想在点击按钮时显示一个弹出菜单，但是这个过程在Delphi XE中出现错误。

procedure ShowPopupMenuEx(var mb1:TMouseButton;var X:integer;var Y:integer;var pPopUP:TPopupMenu);
var
  popupPoint : TPoint;
begin
  if (mb1 = mbLeft) then begin
    popupPoint.X := x ;
    popupPoint.Y := y ;
    popupPoint := ClientToScreen(popupPoint);   //Error Here
    pPopUP.Popup(popupPoint.X, popupPoint.Y) ;   
  end;
end;

procedure TForm1.Button1MouseUp(Sender: TObject; Button: TMouseButton;Shift: TShiftState; X, Y: Integer);
begin
  ShowPopupMenuEx(button,Button1.Left,Button1.Top,PopupMenu1); //Error Here
end;

当点击按钮时显示此错误:

[DCC Error] Form1.pas(205): E2010 Incompatible types: 'HWND' and 'TPoint'
[DCC Error] Form1.pas(398): E2197 Constant object cannot be passed as var parameter
[DCC Error] Form1.pas(398): E2197 Constant object cannot be passed as var parameter

点击按钮时显示弹出菜单有更好的方法吗？

Answer 1

就这么做

procedure TForm1.Button1Click(Sender: TObject);
var
  pnt: TPoint;
begin
  if GetCursorPos(pnt) then
    PopupMenu1.Popup(pnt.X, pnt.Y);
end;

更多讨论

如果您出于某种原因需要使用OnMosuseUp，您可以这样做

procedure TForm1.Button1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  pnt: TPoint;
begin
  if (Button = mbLeft) and GetCursorPos(pnt) then
    PopupMenu1.Popup(pnt.X, pnt.Y);
end;

您的代码不起作用，因为

1. ClientToScreen 是带有签名的 Windows API 的函数

   function ClientToScreen(hWnd: HWND; var lpPoint: TPoint): BOOL;
   

   但是，还有一个带有签名的TControl.ClientToScreen

   function TControl.ClientToScreen(const Point: TPoint): TPoint;
   

   因此，如果您使用的是类方法，则该类是 TControl 的后代，ClientToScreen 将引用后者。如果没有，则引用前一个。当然，这个需要知道我们要从哪个窗口转换坐标!

2. 此外，如果您声明

   var mb1: TMouseButton
   

   作为参数，则仅接受 TMouseButton 类型的变量。但我看不出您有任何理由想要您的 ShowPopupMenuEx 函数的签名。事实上，我认为根本不需要这样的功能......

替代方案

我上面的代码将在光标位置弹出菜单。如果您需要相对于按钮的一个角固定该点，您可以这样做

// Popup at the top-left pixel of the button
procedure TForm1.Button1Click(Sender: TObject);
begin
  with Button1.ClientToScreen(point(0, 0)) do
    PopupMenu1.Popup(X, Y);
end;

// Popup at the bottom-right pixel of the button
procedure TForm1.Button1Click(Sender: TObject);
begin
  with Button1.ClientToScreen(point(Button1.Width, Button1.Height)) do
    PopupMenu1.Popup(X, Y);
end;

// Popup at the bottom-left pixel of the button
procedure TForm1.Button1Click(Sender: TObject);
begin
  with Button1.ClientToScreen(point(0, Button1.Height)) do
    PopupMenu1.Popup(X, Y);
end;