继承的应用-为ComboBox控件添加图片

继承的应用-为ComboBox控件添加图片 为ComboBox控件添加图片 .NET自带的ComboBox控件没有添加图片的功能，在我们学习了继承以后，我们可以继承原有的ComboBox的功能并且加入扩展的新功能。 下面我们对ComboBox进行扩展，实现在ComboBox中显示图片的功能: 1.添加类 ComboBoxExItem: class ComboBoxExItem { private string _text; public string Text { get { return _text; } set { _text = value; } } private int _imageIndex; public int ImageIndex { get { return _imageIndex; } set { _imageIndex = value; } } public ComboBoxExItem() : this("") { } public ComboBoxExItem(string text) : this(text, -1) { } public ComboBoxExItem(string text, int imageIndex) { _text = text; _imageIndex = imageIndex; } public override string ToString() { return _text; } } 2.添加类:ComboBoxEx class ComboBoxEx : ComboBox { private ImageList imageList; public ImageList ImageList { get { return imageList; } set { imageList = value; } } public ComboBoxEx() { DrawMode = DrawMode.OwnerDrawFixed; } protected override void OnDrawItem(DrawItemEventArgs ea) { ea.DrawBackground(); ea.DrawFocusRectangle(); ComboBoxExItem item; Size imageSize = imageList.ImageSize; Rectangle bounds = ea.Bounds; try { item = (ComboBoxExItem)Items[ea.Index]; if (item.ImageIndex != -1) { imageList.Draw(ea.Graphics, bounds.Left, bounds.Top, item.ImageIndex); ea.Graphics.DrawString(item.Text, ea.Font, new SolidBrush(ea.ForeColor), bounds.Left + imageSize.Width, bounds.Top); } else { 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); } } 当上述两个步骤完成之后，我们就可以使用ComboBoxEx来代替ComboBox来实现带图片的ComboBox了 以下是应用的代码:(窗体的加载代码) private void InitializeComponent() { this.components = new System.ComponentModel.Container(); ComboBoxExItem comboBoxExItem1 = new ComboBoxExItem(); ComboBoxExItem comboBoxExItem2 = new ComboBoxExItem(); ComboBoxExItem comboBoxExItem3 = new ComboBoxExItem(); System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(Form1)); this.comboBox1 = new ComboBoxEx(); this.imageList1 = new System.Windows.Forms.ImageList(this.components); this.SuspendLayout(); // // comboBox1 // this.comboBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed; this.comboBox1.ImageList = this.imageList1; comboBoxExItem1.ImageIndex = 0; comboBoxExItem1.Text = "【IT精彩世界】"; comboBoxExItem2.ImageIndex = 1; comboBoxExItem2.Text = "【IT精彩世界】"; comboBoxExItem3.ImageIndex = 2; comboBoxExItem3.Text = "【IT精彩世界】"; this.comboBox1.Items.AddRange(new object[] { comboBoxExItem1, comboBoxExItem2, comboBoxExItem3}); this.comboBox1.Location = new System.Drawing.Point(48, 109); this.comboBox1.Name = "comboBox1"; this.comboBox1.Size = new System.Drawing.Size(200, 22); this.comboBox1.TabIndex = 0; // // imageList1 // this.imageList1.ImageStream = ((System.Windows.Forms.ImageListStreamer)(resources.GetObject("imageList1.ImageStream"))); this.imageList1.TransparentColor = System.Drawing.Color.Transparent; this.imageList1.Images.SetKeyName(0, "welcome.JPG"); this.imageList1.Images.SetKeyName(1, "welcome.JPG"); this.imageList1.Images.SetKeyName(2, "welcome.JPG"); // // Form1 // this.AutoScaleBaseSize = new System.Drawing.Size(6, 14); this.ClientSize = new System.Drawing.Size(292, 273); this.Controls.Add(this.comboBox1); this.Name = "Form1"; this.Text = "Form1"; this.ResumeLayout(false); }