如何在Windows窗体状态栏上启用双缓冲？

Question

有没有办法在Windows窗体StatusBar类上启用双缓冲？

我正在更新鼠标移动事件上的一些地图坐标，并且闪烁/重绘非常明显。我试过从StatusBar类继承并设置它的DoubleBuffer = true并覆盖它的OnPaintBackground方法。我也尝试了所有者绘制的东西，没有任何运气。

Answer 1

System.Windows.Forms.StatusBar是一个传统控件，它可能不关心DoubleBuffered属性。您可以尝试在派生类的构造函数设置它像这样：

this.SetStyle(ControlStyles.DoubleBuffer, true);

虽然我真的建议尝试StatusStrip控制。它适用于Windows窗体，而不是由操作系统绘制，而StatusBar是。

Answer 2

//declare a renderer, but do not initialize in here, 
//because if current theme is classics, it will error 
VisualStyleRenderer _barRenderer; 

protected override void WndProc(ref Message m) 
{ 
    switch (m.Msg) 
    { 
     //eat WM_ERASEBKGND, and in WM_PAINT draw the background 
     case 0x14: 
      m.Result = (IntPtr)1; 
      return; 

     case 0xF://WM_PAINT 
      PAINTSTRUCT ps; 
      var hdc = BeginPaint(m.HWnd, out ps); //see MSDN 
      BufferedGraphics bg = null; //use memory graphics 
      try 
      { 
       var rect = ClientRectangle; 
       bg = BufferedGraphicsManager.Current.Allocate(hdc, rect); 

       //draw background 
       if (Application.RenderWithVisualStyles) 
       { 
        //just initialize renderer once 
        if (_barRenderer == null) 
        { 
         _barRenderer = new VisualStyleRenderer(VisualStyleElement.Status.Bar.Normal); 
        } 
        _barRenderer.DrawBackground(bg.Graphics, rect); 
       } 
       else 
       { 
        bg.Graphics.SetClip(rect); //not essential 
        bg.Graphics.Clear(SystemColors.Control); 
       } 

       //let system draw foreground, include texts, icons, separators etc 
       m.WParam = bg.Graphics.GetHdc(); //required, GetHdc() is not only obtain a dc handle, 
       base.WndProc(ref m);    //it open a context for the dc, and let system draw on this context 
       bg.Graphics.ReleaseHdc();  //timely release 

       bg.Render(); 
       return; 
      } 
      finally 
      { 
       if (bg != null) { bg.Dispose(); } 
       EndPaint(m.HWnd, ref ps); //see MSDN 
      } 
    } 
    base.WndProc(ref m); 
} 

#region Win32 API 

[DllImport("user32.dll")] 
private static extern IntPtr BeginPaint(IntPtr hWnd, out PAINTSTRUCT lpPaint); 

[DllImport("user32.dll")] 
private static extern bool EndPaint(IntPtr hWnd, ref PAINTSTRUCT lpPaint); 

[StructLayout(LayoutKind.Sequential)] 
private struct PAINTSTRUCT 
{ 
    public IntPtr hdc; 
    public bool fErase; 
    public RECT rcPaint; 
    public bool fRestore; 
    public bool fIncUpdate; 
    public int reserved1; 
    public int reserved2; 
    public int reserved3; 
    public int reserved4; 
    public int reserved5; 
    public int reserved6; 
    public int reserved7; 
    public int reserved8; 
} 

[StructLayout(LayoutKind.Sequential)] 
private struct RECT 
{ 
    public int Left; 
    public int Top; 
    public int Right; 
    public int Bottom; 
} 

#endregion