在 WM_PAINT 中绘制的文本框在鼠标 enter/leave 上闪烁

Question

我有一个自定义文本框，当它为空时我会在其中绘制一些占位符文本。它工作得很好，但是当鼠标进入和离开 TextBox 时它会闪烁。这似乎与鼠标悬停在控件上时边框变蓝有关（我在 Windows 8.1）。

知道如何解决这个问题吗？

我试过各种 SetStyles 标志但都没有成功。

class MyTextBox : TextBox
{
  public string PlaceHolder { get; set; }

  static readonly Brush sPlaceHolderBrush = new SolidBrush(Color.FromArgb(70, 70, 78));
  static readonly StringFormat sFormat = new StringFormat
  {
     Alignment = StringAlignment.Near,
     LineAlignment = StringAlignment.Center
  };

  private Font mPlaceHolderFont;

  [DllImport("user32")]
  private static extern IntPtr GetWindowDC(IntPtr hwnd);

  protected override void WndProc(ref Message m)
  {
     base.WndProc(ref m);

     if (m.Msg == 0x0F)   
     {
        if (string.IsNullOrEmpty(Text) && !Focused)
        {
           IntPtr dc = GetWindowDC(Handle);
           using (Graphics g = Graphics.FromHdc(dc))
           {
              if (mPlaceHolderFont == null)
                 mPlaceHolderFont = new Font(Font, FontStyle.Italic);

              var rect = new RectangleF(2, 2, Width - 4, Height - 4);
              g.FillRectangle(Brushes.White, rect);
              g.DrawString(PlaceHolder, mPlaceHolderFont, sPlaceHolderBrush, rect, sFormat);
           }
        }
     }
  }
}

我在覆盖 OnPaint 时遇到了其他问题。这是我想出的最佳解决方案：

class MyTextBox : TextBox
{
  public string PlaceHolder { get; set; }

  static readonly Brush sPlaceHolderBrush = new SolidBrush(Color.FromArgb(70, 70, 78));
  static readonly StringFormat sFormat = new StringFormat
  {
     Alignment = StringAlignment.Near,
     LineAlignment = StringAlignment.Near
  };

  private Font mPlaceHolderFont;
  private Brush mForegroundBrush;

  protected override void OnHandleCreated(EventArgs e)
  {
     base.OnHandleCreated(e);
     SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.DoubleBuffer | ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint, true);
  }

  protected override void OnPaint(PaintEventArgs e)
  {
     var bounds = new Rectangle(-2, -2, Width, Height);
     var rect = new RectangleF(1, 0, Width - 2, Height - 2);

     e.Graphics.FillRectangle(Brushes.White, rect);
     if (string.IsNullOrEmpty(Text) && !Focused)
     {
        if (mPlaceHolderFont == null)
           mPlaceHolderFont = new Font(Font, FontStyle.Italic);

        if (mForegroundBrush == null)
           mForegroundBrush = new SolidBrush(ForeColor);

        e.Graphics.DrawString(PlaceHolder, mPlaceHolderFont, sPlaceHolderBrush, rect, sFormat);
     }
     else
     {
        var flags = TextFormatFlags.Default | TextFormatFlags.TextBoxControl;
        if (!Multiline)
           flags |= TextFormatFlags.SingleLine | TextFormatFlags.NoPadding;

        TextBoxRenderer.DrawTextBox(e.Graphics, bounds, Text, Font, flags, TextBoxState.Selected);
     }
  }
}

Answer 1

使用 WM_PAINT 而不是 OnPaint 是否有特殊原因？在 WM_PAINT 中，您从句柄获取绘图上下文，这始终是对控件的直接访问。在 OnPaint 中，事件参数中已经有一个 Graphics，它可以是缓冲区或直接上下文，具体取决于样式。

您提到您尝试了几种样式但没有成功。首先我会说尝试这些和将你的绘画逻辑移动到 OnPaint:

SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.DoubleBuffer | ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint, true);

如果它不起作用（聚焦控件在 Windows 中可能表现异常）并且您必须坚持使用 WM_PAINT，然后手动创建缓冲区。您的原始代码首先绘制一个白色矩形，然后绘制一些文本，这会导致闪烁。您可以通过使用缓冲区来避免这种情况：

IntPtr dc = GetWindowDC(Handle);
using (Graphics g = Graphics.FromHdc(dc))
{
    // creating a buffered context
    using (BufferedGraphicsContext context = new BufferedGraphicsContext())
    {
        // creating a buffer for the original Graphics
        using (BufferedGraphics bg = context.Allocate(e.Graphics, ClientRectangle))
        {
             if (mPlaceHolderFont == null)
                mPlaceHolderFont = new Font(Font, FontStyle.Italic);

             var gBuf = bg.Graphics;
             var rect = ClientRectangle;
             rect.Inflate(-1, -1);
             gBuf.FillRectangle(Brushes.White, rect);
             gBuf.DrawString(PlaceHolder, mPlaceHolderFont, sPlaceHolderBrush, rect, sFormat);

             // copying the buffer onto the original Graphics
             bg.Render(e.Graphics);
        }
    }
}

在 WM_PAINT 中绘制的文本框在鼠标 enter/leave 上闪烁

TextBox drawn in WM_PAINT flickers on mouse enter/leave

c#

winforms

textbox

gdi+

wm-paint