下面是我写的一个扩展combobox控件的例子
using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Windows.Forms;
namespace ComboBoxEx
{
public class ComboBoxEx:ComboBox
{
ListBox lst=new ListBox();
public ComboBoxEx()
{
lst.SelectionMode=SelectionMode.MultiExtended;
this.DrawMode=DrawMode.OwnerDrawFixed;//只有设置这个属性为OwnerDrawFixed才可能让重画起作用
lst.KeyUp+=new KeyEventHandler(lst_KeyUp);
lst.MouseUp+=new MouseEventHandler(lst_MouseUp);
lst.KeyDown+=new KeyEventHandler(lst_KeyDown);
}
#region Property
[Description("选定项的值"),Category("Data")]
public ListBox.SelectedObjectCollection SelectedItems
{
get
{
return lst.SelectedItems;
}
}
#endregion
#region override
protected override void OnKeyUp(KeyEventArgs e)
{
base.OnKeyDown(e);
bool Pressed=(e.Control && ((e.KeyData & Keys.A)==Keys.A));
if(Pressed)
{
for(int i=0;i<lst.Items.Count;i++)
lst.SetSelected(i,true);
}
}
protected override void OnMouseDown(MouseEventArgs e)
{
this.DroppedDown=false;
}
protected override void OnMouseUp(MouseEventArgs e)
{
this.DroppedDown=false;
lst.Focus();
}
protected override void OnDropDown(EventArgs e)
{
lst.Items.Clear();
lst.Show();
lst.ItemHeight=this.ItemHeight;
lst.BorderStyle=BorderStyle.FixedSingle;
lst.Size=new Size(this.DropDownWidth,this.ItemHeight*(this.MaxDropDownItems-1)-(int)this.ItemHeight/2);
lst.Location=new Point(this.Left,this.Top+this.ItemHeight+6);
lst.BeginUpdate();
for(int i=0;i<this.Items.Count;i++)
lst.Items.Add(this.Items[i]);
lst.EndUpdate();
this.Parent.Controls.Add(lst);
}
#endregion
private void lst_KeyUp(object sender, KeyEventArgs e)
{
this.OnKeyUp(e);
}
private void lst_MouseUp(object sender, MouseEventArgs e)
{
try
{
this.Text="";
for(int i=0;i<lst.SelectedItems.Count;i++)
{
if(i==0)
this.Text=lst.SelectedItems[i].ToString();
else
{
this.Text=this.Text+","+lst.SelectedItems[i].ToString();
}
}
}
catch
{
this.Text="";
}
bool isControlPressed=(Control.ModifierKeys==Keys.Control);
bool isShiftPressed=(Control.ModifierKeys==Keys.Shift);
if(isControlPressed || isShiftPressed)
lst.Show();
else
lst.Hide();
}
private void lst_KeyDown(object sender, KeyEventArgs e)
{
switch(e.KeyData)
{
case Keys.Down:
if(lst.SelectedItems.Count!=0)
{
this.Text=lst.SelectedItem.ToString();
}
else
this.Text=this.Items[0].ToString();
break;
case Keys.Up:
if(lst.SelectedItems.Count!=0)
{
this.Text=lst.SelectedItem.ToString();
}
else
this.Text=this.Items[0].ToString();
break;
}
}
}
}
如果有什么不理解的可以加我ＱＱ，不过在加的时候要说明原因．ＱＱ：３４７９５１７３ 
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