爲什麼在MouseMove事件中調用WindowFromPoint時突出顯示窗體的系統按鈕？

Question

在傳遞給WindowFromPoint的點處，在TWinControl的MouseMove事件中調用WindowFromPoint會導致MouseOver事件。這是一個VCL錯誤？有人知道是否有解決方法？

這裏的演示代碼：

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 

我用Delphi XE2在Windows 7專業版64位。我也可以使用Delphi 7複製。

Answer 1

我用最簡單的C++應用程序測試了這個，並觀察到相同的行爲，這不是VCL錯誤（正如David在評論中提到的那樣）。這與鼠標移動無關順便說一句，任何時候當您通過字幕按鈕的座標傳遞WindowFromPoint時，都會發生特殊性。它只發生在屬於調用該函數的線程的窗口中。

因此，對於解決方法，您可以從線程調用WindowFromPoint。簡單的例子下面，不是一個真正的後臺線程的代碼等待它完成：

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 

這將是有意義的測試所顯示的bug的條件（OS，主題..），使有條件的代碼可以避免不必要的開銷。