windows – 为什么在MouseMove事件中调用WindowFromPoint时,窗体的系统按钮会突出显示?

在TWinControl的MouseMove事件中调用WindowFromPoint会在传递给WindowFromPoint的点处导致MouSEOver事件.这是一个VCL错误吗?有人知道是否有解决方法

这是演示代码

unit Unit7;

interface

uses
  Winapi.Windows,Winapi.Messages,System.SysUtils,System.Variants,System.Classes,Vcl.Graphics,Vcl.Controls,Vcl.Forms,Vcl.Dialogs,Vcl.StdCtrls;

type
  TForm7 = class(TForm)
    Button1: TButton;
    procedure Button1MouseMove(Sender: TObject; Shift: TShiftState; X,Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form7: TForm7;

implementation

{$R *.dfm}

procedure TForm7.Button1MouseMove(Sender: TObject; Shift: TShiftState; X,Y: Integer);
begin
  WindowFromPoint(Point(Mouse.CursorPos.X,Mouse.CursorPos.Y - 40));
end;

end.

DFM:

object Form7: TForm7
  Left = 0
  Top = 0
  Caption = 'Form7'
  ClientHeight = 40
  ClientWidth = 116
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 24
    Top = 7
    Width = 75
    Height = 25
    Caption = 'Button1'
    TabOrder = 0
    OnMouseMove = Button1MouseMove
  end
end

我在Windows 7 Pro 64bit上使用Delphi XE2.我也可以使用Delphi 7重现.

解决方法

我用最简单的C应用程序对此进行了测试并观察到相同的行为,这不是VCL错误(正如David在评论中提到的那样).它与鼠标移动BTW无关,只要你调用WindowFromPoint传递字幕按钮的坐标,就会出现特殊情况.它只发生在属于调用函数的线程的窗口上.

因此,对于解决方法,您可以从线程调用WindowFromPoint.下面的简单示例,并非真正的后台线程,因为代码等待它完成:

type
  TGetWndThread = class(TThread)
  private
    FPoint: TPoint;
  protected
    procedure Execute; override;
    constructor Create(AOwner: TComponent; Point: TPoint);
  end;

constructor TGetWndThread.Create(AOwner: TComponent; Point: TPoint);
begin
  FPoint := Point;
  inherited Create;
end;

procedure TGetWndThread.Execute;
begin
  ReturnValue := WindowFromPoint(FPoint);
end;

..

var
  Wnd: HWND;
  Thr: TGetWndThread;
begin
  Thr := TGetWndThread.Create(nil,Point(Mouse.CursorPos.X,Mouse.CursorPos.Y - 40));
  Wnd := Thr.WaitFor;
  Thr.Free;
  .. // use Wnd

测试错误显示的条件(操作系统,主题..)并使代码有条件以避免不必要的开销是有意义的.

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