由於專案需要，現有的ComboBox控制元件滿足不了需求，需要重寫做一些小小的改變。要求ComboBox每一項前增加圖片顯示，使邊框顏色修改，及禁用滑鼠滾輪修改當前選項。

定義ComboBox選擇項類

using System; using System.Collections.Generic; using System.Text; namespace ComboBoxControl { public class ImageComboBoxItem { private string _text; /// <summary> /// 文字屬性 /// </summary> public string Text { get { return _text; } set { _text = value; } } private string _value; /// <summary> /// 選擇項的值 /// </summary> public string Value { get { return _value; } set { _value = value; } } private int _imageIndex; /// <summary> /// 定義圖象索引屬性 /// </summary> public int ImageIndex { get { return _imageIndex; } set { _imageIndex = value; } } #region 建構函式 public ImageComboBoxItem() { _text = ""; _imageIndex = -1; } public ImageComboBoxItem(string text) { _text = text; _imageIndex = -1; } public ImageComboBoxItem(string text, int imageIndex) { _text = text; _imageIndex = imageIndex; } public ImageComboBoxItem(string text, int imageIndex, string value) { _text = text; _imageIndex = imageIndex; _value = value; } #endregion public override string ToString() { return _text; } } }

建立使用者控制元件繼承自ComboBox,直接重寫ComboBox的OnPaint方法時卻無法對控制元件進行重繪，

只能用系統訊息對PAINT進行攔截

using System; using System.Collections.Generic; using System.Text; using System.Drawing; using System.Windows.Forms; using System.ComponentModel; namespace ComboBoxControl { public partial class ComboBoxControl : System.Windows.Forms.ComboBox, IMessageFilter//繼承自ComboBox { #region API函式 [System.Runtime.InteropServices.DllImport("user32.dll ")] static extern IntPtr GetWindowDC(IntPtr hWnd);//返回hWnd引數所指定的視窗的裝置環境。 [System.Runtime.InteropServices.DllImport("user32.dll ")] static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC); //函式釋放裝置上下文環境（DC） int WM_PAINT = 0xf; //要求一個視窗重畫自己,即Paint事件時 int WM_CTLCOLOREDIT = 0x133;//當一個編輯型控制元件將要被繪製時傳送此訊息給它的父視窗； #endregion #region 屬性 private ImageList _imageList; /// <summary> /// 需要顯示在選擇項前的圖示 /// </summary> [ Category("自定義屬性"), Description("需要顯示在選擇項前的圖示集合") ] public ImageList ImageList { get { return _imageList; } set { _imageList = value; } } private Color _bdColor; /// <summary> /// 邊框顏色 /// </summary> [ Category("自定義屬性"), Description("設定邊框顏色") ] public Color BdColor { get { return _bdColor; } set { _bdColor = value; } } private int _bdSize = 1; /// <summary> /// 邊框粗細 /// </summary> [ Category("自定義屬性"), Description("設定邊框粗細") ] public int BdSize { get { return _bdSize; } set { _bdSize = value; } } private bool _disableWheel = false; /// <summary> /// 是否禁用滑鼠滾輪 /// </summary> [ Category("自定義屬性"), Description("是否禁用滑鼠滾輪來更改當前選項") ] public bool DisableWheel { get { return _disableWheel; } set { _disableWheel = value; } } #endregion public ComboBoxControl() { InitializeComponent(); DrawMode = DrawMode.OwnerDrawFixed;//設定繪畫模式為手動 } protected override void WndProc(ref Message m) { base.WndProc(ref m); if (m.Msg == WM_PAINT || m.Msg == WM_CTLCOLOREDIT) { IntPtr hDC = GetWindowDC(m.HWnd); if (hDC.ToInt32() == 0) //如果取裝置上下文失敗則返回 { return; } //建立Graphics對像 Graphics g = Graphics.FromHdc(hDC); Pen p = new Pen(_bdColor, _bdSize); //畫邊框 g.DrawRectangle(p, 0, 0, Width, Height); ReleaseDC(m.HWnd, hDC); } } //過載OnDrawItem函式，來繪製組合框中每一列表項 protected override void OnDrawItem(DrawItemEventArgs ea) { ea.DrawBackground(); ea.DrawFocusRectangle(); ImageComboBoxItem item; Size imageSize = new Size(); if (ImageList != null) { imageSize = _imageList.ImageSize; } Rectangle bounds = ea.Bounds; try { item = (ImageComboBoxItem)Items[ea.Index]; //如果當前項既有影象又有文字 if (item.ImageIndex != -1) { //畫影象 _imageList.Draw(ea.Graphics, bounds.Left, bounds.Top, item.ImageIndex); //繪製文字 ea.Graphics.DrawString(item.Text, ea.Font, new SolidBrush(ea.ForeColor), bounds.Left + imageSize.Width, bounds.Top); } else//只有文字，沒有影象 { //寫文字 ea.Graphics.DrawString(item.Text, ea.Font, new SolidBrush(ea.ForeColor), bounds.Left, bounds.Top); } } catch { if (ea.Index != -1) { ea.Graphics.DrawString(Items[ea.Index].ToString(), ea.Font, new SolidBrush(ea.ForeColor), bounds.Left, bounds.Top); } else { ea.Graphics.DrawString(Text, ea.Font, new SolidBrush(ea.ForeColor), bounds.Left, bounds.Top); } } base.OnDrawItem(ea); } #region IMessageFilter 成員 /// <summary> /// 訊息篩選器 /// </summary> /// <param name="m"></param> /// <returns></returns> public bool PreFilterMessage(ref Message m) { //攔截0x020A滑鼠滾輪訊息 if (m.Msg == 0x020A && _disableWheel) return true; return false; } #endregion } }

Demo

private void Form1_Load(object sender, EventArgs e) { List<ImageComboBoxItem> items = new List<ImageComboBoxItem>(); for (int i = 0; i < 3; i++) { ImageComboBoxItem item = new ImageComboBoxItem(i.ToString(), i, i.ToString()); items.Add(item); } comboBoxControl1.ImageList = imageList1; comboBoxControl1.DataSource = items; comboBoxControl1.ValueMember = "value"; }