TreeView本身不支持透明背景，重写WndProc以支持背景图片。
using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
using System.ComponentModel;
using System.Runtime.InteropServices;
namespace MyControl
{
/// <summary>
/// Displays a hierarchical collection of labeled items, each represented by a System.Windows.Forms.TreeNode.
/// </summary>
[
//Use the same attibutes as TreeView
DesignerAttribute("System.Windows.Forms.Design.TreeViewDesigner, System.Design, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"),
DefaultPropertyAttribute("Nodes"),
DefaultEventAttribute("AfterSelect")
]
public class UTreeView : TreeView
{
Bitmap internalBitmap = null;
Graphics internalGraphics = null;
Image image = null;
private void DisposeInternal()
{
if (internalGraphics != null)
internalGraphics.Dispose();
if (internalBitmap != null)
internalBitmap.Dispose();
}
/// <summary>Releases resources.</summary>
/// <param name="disposing">true = Both managed and unmanaged, false = Unmanaged only.</param>
protected override void Dispose(bool disposing)
{
if (disposing)
DisposeInternal();
base.Dispose(disposing);
}
/// <summary>Occurs when window is resized.</summary>
/// <param name="e">A System.EventArgs.Empty.</param>
/// <remarks>Recreates internal Graphics object. </remarks>
protected override void OnResize(System.EventArgs e)
{
if (internalBitmap == null ||
internalBitmap.Width != Width || internalBitmap.Height != Height)
{
if (Width != 0 && Height != 0)
{
DisposeInternal();
internalBitmap = new Bitmap(Width, Height);
internalGraphics = Graphics.FromImage(internalBitmap);
}
}
}
/// <summary>Occurs when a Windows message is dispatched.</summary>
/// <param name="message">Message to process.</param>
/// <remarks>Overrides WM_PAINT, WM_ERASEBKGND.</remarks>
public void setBackGround(Image bk = null)
{
if (bk != null)
{
image = bk;
}
else
{
Bitmap bm = new Bitmap(this.Parent.BackgroundImage, this.Parent.Width, this.Parent.Height);
//绘制矩形，定义你需要截取的图像起始位置和宽高
Rectangle rs = new Rectangle(this.Location.X, this.Location.Y, this.Width, this.Height);
//按矩形尺寸和起始位置截取bm的一部分
bm = bm.Clone(rs, System.Drawing.Imaging.PixelFormat.Undefined);
image = bm;
}
}
/// <summary>Occurs when a Windows message is dispatched.</summary>
/// <param name="message">Message to process.</param>
/// <remarks>Overrides WM_PAINT, WM_ERASEBKGND.</remarks>
protected override void WndProc(ref Message message)
{
const int WM_PAINT = 0x000F;
const int WM_PRINTCLIENT = 0x0318;
const int WM_ERASEBKGND = 0x0014;
switch (message.Msg)
{
case WM_ERASEBKGND:
return;
case WM_PAINT:
// The designer host does not call OnResize()
if (internalGraphics == null)
OnResize(EventArgs.Empty);
//Set up
Win32.RECT updateRect = new Win32.RECT();
if (Win32.GetUpdateRect(message.HWnd, ref updateRect, false) == 0)
break;
//Draw Internal Graphics
IntPtr hdc = internalGraphics.GetHdc();
Message printClientMessage = Message.Create(Handle, WM_PRINTCLIENT, hdc, IntPtr.Zero);
DefWndProc(ref printClientMessage);
internalGraphics.ReleaseHdc(hdc);
//Add the missing OnPaint() call
OnPaint(new PaintEventArgs(internalGraphics, Rectangle.FromLTRB(
updateRect.left,
updateRect.top,
updateRect.right,
updateRect.bottom)));
Win32.PAINTSTRUCT paintStruct = new Win32.PAINTSTRUCT();
//IntPtr screenHdc1 = Win32.BeginPaint(message.HWnd, ref paintStruct);
IntPtr screenHdc = Win32.GetDC(message.HWnd);
using (Graphics screenGraphics = Graphics.FromHdc(screenHdc))
{
//Draw Screen Graphics
Bitmap temp = new Bitmap(internalBitmap, internalBitmap.Size);
temp.MakeTransparent(Color.White);
internalGraphics.FillRectangle(Brushes.White, 0, 0, this.Bounds.Width, this.Bounds.Height);
if (image != null)
internalGraphics.DrawImage(image, 0, 0, image.Width, image.Height);
internalGraphics.DrawImage(temp, 0, 0, temp.Width, temp.Height);
screenGraphics.DrawImage(internalBitmap, 0, 0);
}
//Tear down
int ret = Win32.ReleaseDC(message.HWnd, screenHdc);
Win32.ValidateRect(message.HWnd, ref updateRect);
//Win32.EndPaint( message.HWnd, ref paintStruct );
return;
}
base.WndProc(ref message);
}
/// <summary>Occurs when the control is redrawn.</summary>
/// <remarks>Re enable browsing attributes for the Paint Event.</remarks>
[
EditorBrowsableAttribute(EditorBrowsableState.Always),
BrowsableAttribute(true)
]
public new event PaintEventHandler Paint
{
add { base.Paint += value; }
remove { base.Paint -= value; }
}
}
/// <summary>
/// Win32 PInvoke declarations
/// </summary>
internal class Win32
{
[DllImport("User32.dll")]
public static extern int GetUpdateRect(IntPtr hwnd, ref RECT rect, bool erase);
[DllImport("User32.dll")]
public static extern int ValidateRect(IntPtr hwnd, ref RECT rect);
[DllImport("User32.dll", SetLastError = true)]
public static extern bool GetWindowRect(IntPtr handle, ref RECT rect);
[DllImport("User32.dll")]
public static extern IntPtr BeginPaint(IntPtr hWnd, ref PAINTSTRUCT paintStruct);
[DllImport("User32.dll")]
public static extern bool EndPaint(IntPtr hWnd, ref PAINTSTRUCT paintStruct);
[DllImport("User32.dll")]
public static extern IntPtr GetDC(IntPtr hWnd);
[DllImport("User32.dll")]
public static extern int ReleaseDC(IntPtr hwnd, IntPtr hdc);
[DllImport("User32.dll")]
public static extern int SendMessage(IntPtr hwnd, uint uMsg, IntPtr wParam, IntPtr lParam);
[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
public int left;
public int top;
public int right;
public int bottom;
}
[StructLayout(LayoutKind.Sequential)]
public struct PAINTSTRUCT
{
public IntPtr hdc;
public int fErase;
public RECT rcPaint;
public int fRestore;
public int 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;
}
}
}