C# 绘制透明按钮

Drawing a transparent button

提问by rein

I'm trying to create a transparent button in C# (.NET 3.5 SP1) to use in my WinForms application. I've tried everything to get the button to be transparent (it should show the gradient background underneath the button) but it's just not working.

我正在尝试在 C# (.NET 3.5 SP1) 中创建一个透明按钮以在我的 WinForms 应用程序中使用。我已经尝试了所有方法来使按钮透明（它应该在按钮下方显示渐变背景），但它不起作用。

Here is the code I'm using:

这是我正在使用的代码：

public class ImageButton : ButtonBase, IButtonControl
{
    public ImageButton()
    {
        this.SetStyle(
            ControlStyles.SupportsTransparentBackColor | 
            ControlStyles.OptimizedDoubleBuffer | 
            ControlStyles.AllPaintingInWmPaint | 
            ControlStyles.ResizeRedraw | 
            ControlStyles.UserPaint, true);
        this.BackColor = Color.Transparent;
    }

    protected override void OnPaint(PaintEventArgs pevent)
    {
        Graphics g = pevent.Graphics;
        g.FillRectangle(Brushes.Transparent, this.ClientRectangle);
        g.DrawRectangle(Pens.Black, this.ClientRectangle);
    }


    // rest of class here...

}

The problem is that the button seems to be grabbing random UI memory from somewhere and filling itself with some buffer from Visual Studio's UI (when in design mode). At runtime it's grabbing some zero'd buffer and is completely black.

问题是按钮似乎从某处获取随机 UI 内存并用 Visual Studio 的 UI 中的一些缓冲区填充自己（在设计模式下）。在运行时，它正在抓取一些零缓冲区并且完全是黑色的。

My ultimate goal is to paint an image on an invisible button instead of the rectangle. The concept should stay the same however. When the user hovers over the button then a button-type shape is drawn.

我的最终目标是在不可见的按钮而不是矩形上绘制图像。然而，这个概念应该保持不变。当用户将鼠标悬停在按钮上时，会绘制一个按钮类型的形状。

Any ideas?

有任何想法吗？

EDIT: Thanks everybody, the following worked for me:

编辑：谢谢大家，以下对我有用：

public class ImageButton : Control, IButtonControl
{
    public ImageButton()
    {
        SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        SetStyle(ControlStyles.Opaque, true);
        SetStyle(ControlStyles.ResizeRedraw, true);
        this.BackColor = Color.Transparent;

    }

    protected override void OnPaint(PaintEventArgs pevent)
    {
        Graphics g = pevent.Graphics;
        g.DrawRectangle(Pens.Black, this.ClientRectangle);
    }


    protected override void OnPaintBackground(PaintEventArgs pevent)
    {
        // don't call the base class
        //base.OnPaintBackground(pevent);
    }


    protected override CreateParams CreateParams
    {
        get
        {
            const int WS_EX_TRANSPARENT = 0x20;
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= WS_EX_TRANSPARENT;
            return cp;
        }
    }

    // rest of class here...
}

采纳答案by arbiter

WinForms (and underlying User32) does not support transparency at all. WinForms however can simulate transparency by using control style you provide - SupportsTransparentBackColor, but in this case all that "transparent" control does, it to allow drawing parent its background.

WinForms（和底层 User32）根本不支持透明度。然而，WinForms 可以通过使用您提供的控件样式来模拟透明度 - SupportsTransparentBackColor，但在这种情况下，所有“透明”控件所做的都是允许绘制父级的背景。

ButtonBase uses some windows styles that prevent working this mechanism. I see two solutions: one is to derive your control from Control (instead of ButtonBase), and second is to use Parent's DrawToBitmap to get background under your button, and then draw this image in OnPaint.

ButtonBase 使用了一些阻止使用此机制的窗口样式。我看到两种解决方案：一是从Control（而不是ButtonBase）派生控件，二是使用Parent的DrawToBitmap获取按钮下的背景，然后在OnPaint中绘制此图像。

回答by Dan Bystr?m

I'm not sure ButtonBase supports transparency... have you checked that out?

我不确定 ButtonBase 是否支持透明度......你有没有检查过？

I've written a number of transparent controls, but I have always inherited from Control or UserControl.

我写了一些透明控件，但我总是从 Control 或 UserControl 继承。

When you want to block out a control painting it's background - you should override OnPaintBackground instead of OnPaint and not call the base class.

当您想要阻止绘制控件的背景时 - 您应该覆盖 OnPaintBackground 而不是 OnPaint 并且不要调用基类。

Filling a rectangle with Brushes.Transparent is funny though - you're painting with an invisible color over what's aready there. Or to put it another way: it does nothing!

用 Brushes.Transparent 填充一个矩形很有趣 - 你正在用一种不可见的颜色来绘制那里的区域。或者换句话说：它什么都不做！

回答by jmservera

In winforms there are some tricks to allow a control having its background correctly painted when using transparency. You can add this code to the OnPaint or OnPaintBackground to get the controls you have in the background being painted:

在 winforms 中，有一些技巧可以让控件在使用透明度时正确绘制其背景。您可以将此代码添加到 OnPaint 或 OnPaintBackground 以获取正在绘制的背景中的控件：

if (this.Parent != null)
{
 GraphicsContainer cstate = pevent.Graphics.BeginContainer();
 pevent.Graphics.TranslateTransform(-this.Left, -this.Top);
 Rectangle clip = pevent.ClipRectangle;
 clip.Offset(this.Left, this.Top);
 PaintEventArgs pe = new PaintEventArgs(pevent.Graphics, clip);

 //paint the container's bg
 InvokePaintBackground(this.Parent, pe);
 //paints the container fg
 InvokePaint(this.Parent, pe);
 //restores graphics to its original state
 pevent.Graphics.EndContainer(cstate);
}
else
  base.OnPaintBackground(pevent); // or base.OnPaint(pevent);...

回答by Kevin

I know this question is old, but if someone doesn't want to create a control to do this I came up with this code from a different article and changed it an extension method.

我知道这个问题很旧，但是如果有人不想创建控件来执行此操作，我会从另一篇文章中提出此代码并将其更改为扩展方法。

public static void ToTransparent(this System.Windows.Forms.Button Button,
     System.Drawing.Color TransparentColor)
{
    Bitmap bmp = ((Bitmap)Button.Image);
    bmp.MakeTransparent(TransparentColor);
    int x = (Button.Width - bmp.Width) / 2;
    int y = (Button.Height - bmp.Height) / 2;
    Graphics gr = Button.CreateGraphics();
    gr.DrawImage(bmp, x, y);
}

And the call like:

调用如下：

buttonUpdate.ToTransparent(Color.Magenta);