winform没有默认的下拉tree的控件可是有些多级的列表需要下拉tree,下面我们的代码实现对Combbox进行扩展让它下拉显示tree.

1. using System.Drawing;  
2. using System.Windows.Forms;  
3. namespace WindowsApplication23  
4. {  
5.     public class ComboBoxTreeView : ComboBox  
6.     {  
7.         private const int WM_LBUTTONDOWN = 0x201, WM_LBUTTONDBLCLK = 0x203;  
8.         ToolStripControlHost treeViewHost;  
9.         ToolStripDropDown dropDown;  
10.         public ComboBoxTreeView()  
11.         {  
12.             TreeView treeView = new TreeView();  
13.             treeView.AfterSelect += new TreeViewEventHandler(treeView_AfterSelect);  
14.             treeView.BorderStyle = BorderStyle.None;  
15.   
16.             treeViewHost = new ToolStripControlHost(treeView);  
17.             dropDown = new ToolStripDropDown();  
18.             dropDown.Width = this.Width;  
19.             dropDown.Items.Add(treeViewHost);  
20.         }  
21.         public void treeView_AfterSelect(object sender, TreeViewEventArgs e)  
22.         {  
23.             this.Text = TreeView.SelectedNode.Text;  
24.             dropDown.Close();  
25.         }  
26.         public TreeView TreeView  
27.         {  
28.             get { return treeViewHost.Control as TreeView; }  
29.         }  
30.         private void ShowDropDown()  
31.         {  
32.             if (dropDown != null)  
33.             {  
34.                 treeViewHost.Size = new Size(DropDownWidth - 2, DropDownHeight);  
35.                 dropDown.Show(this, 0, this.Height);  
36.             }  
37.         }  
38.         protected override void WndProc(ref Message m)  
39.         {  
40.             if (m.Msg == WM_LBUTTONDBLCLK || m.Msg == WM_LBUTTONDOWN)  
41.             {  
42.                 ShowDropDown();  
43.                 return;  
44.             }  
45.             base.WndProc(ref m);  
46.         }  
47.         protected override void Dispose(bool disposing)  
48.         {  
49.             if (disposing)  
50.             {  
51.                 if (dropDown != null)  
52.                 {  
53.                     dropDown.Dispose();  
54.                     dropDown = null;  
55.                 }  
56.             }  
57.             base.Dispose(disposing);  
58.         }  
59.     }  
60.   
61. } 

这只是一个简单的实现，后面我们会把它显示到dataGrid里面。*[电13802269370]  北京*[电13802269370]  郑州*[电13802269370]  深圳*[电13802269370]