c# 可以设置透明度的 Panel 组件

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Text;
using System.Windows.Forms;

namespace TransparentPanelTest
{
public class TransparentPanel : Control
{
private Color _borderColor;
private int _borderWidth = 1;
private DashStyle _borderStyle = DashStyle.Solid;
private int _opacity = 125;

public TransparentPanel()
{

}

#region Property
[Category("Custom"), Description("Border Color")]
public Color BorderColor
{
set { _borderColor = value; }
get { return _borderColor; }
}

[Category("Custom"), Description("Border Width"), DefaultValue(1)]
public int BorderWidth
{
set
{
if (value < 0) value = 0;
_borderWidth = value;
}
get { return _borderWidth; }
}

[Category("Custom"), Description("Border Style"), DefaultValue(DashStyle.Solid)]
public DashStyle BorderStyle
{
set { this._borderStyle = value; this.Invalidate(); }
get { return this._borderStyle; }
}

[Bindable(true), Category("Custom"), DefaultValue(125), Description("背景的透明度. 有效值0-255")]
public int Opacity
{
get { return _opacity; }
set
{
if (value > 255) value = 255;
else if (value < 0) value = 0;
_opacity = value;
this.Invalidate();
}
}
#endregion

protected override void OnPaintBackground(PaintEventArgs e)
{
//do not allow the background to be painted
}

protected override CreateParams CreateParams
{
get
{
CreateParams cp = base.CreateParams;
cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT
return cp;
}
}

protected override void OnPaint(System.Windows.Forms.PaintEventArgs e)
{
if (this._opacity > 0)
{
e.Graphics.FillRectangle(new SolidBrush(Color.FromArgb(this._opacity, this.BackColor)),
this.ClientRectangle);
}
if (this._borderWidth > 0)
{
Pen pen = new Pen(this._borderColor, this._borderWidth);
pen.DashStyle = this._borderStyle;
e.Graphics.DrawRectangle(pen, e.ClipRectangle.Left, e.ClipRectangle.Top, this.Width - 1, this.Height - 1);
pen.Dispose();
}
}

}
}