ComboBox 类详解

ComboBox 类

表示 Windows 组合框控件。

有关此类型所有成员的列表，请参阅 ComboBox 成员。

System.Object
   System.MarshalByRefObject
      System.ComponentModel.Component
         System.Windows.Forms.Control
            System.Windows.Forms.ListControl
               System.Windows.Forms.ComboBox

[Visual Basic]

Public Class ComboBox

   Inherits ListControl

[C#]

public class ComboBox : ListControl

[C++]

public __gc class ComboBox : public ListControl

[JScript]

public class ComboBox extends ListControl

线程安全

此类型的所有公共静态（Visual Basic 中为 Shared）成员是线程安全的。但不保证任何实例成员是线程安全的。

备注

ComboBox 显示与一个 ListBox 组合的编辑字段，使用户可以从列表中选择或输入新文本。ComboBox 的默认行为是显示一个编辑字段，该字段附带一个隐藏的下拉列表。DropDownStyle 属性确定要显示的组合框的样式。您可以输入一个值，该值指示允许以下情况：简单的下拉列表（始终显示列表）、下拉列表框（文本部分不可编辑，并且必须选择一个箭头才能查看下拉列表框）或默认下拉列表框（文本部分可编辑，并且用户必须按箭头键才能查看列表）。若要始终显示用户不能编辑的列表，请使用 ListBox 控件。

若要在运行时向列表添加对象，请用 AddRange 方法分配一个对象引用数组。然后，列表显示每个对象的默认字符串值。可以用 Add 方法添加单个对象。

除显示和选择功能外，ComboBox 还提供一些功能使您能够有效地向 ComboBox 添加项以及在列表项内查找文本。BeginUpdate 和 EndUpdate 方法使您能够向 ComboBox 添加大量项而不必在每次向列表添加项时重新绘制控件。FindString 和 FindStringExact 方法使您能够在列表中搜索包含特定搜索字符串的项。

可以使用这些属性管理列表中当前选定的项，使用 Text 属性指定编辑字段中显示的字符串，使用 SelectedIndex 属性获取或设置当前项，以及使用 SelectedItem 属性获取或设置对对象的引用。

示例

[Visual Basic, C#, C++] 下面的示例是个完整的应用程序，阐释可如何使用 Add 方法向 ComboBox 添加项，如何使用 FindString 方法在 ComboBox 中查找项，以及如何使用 BeginUpdate 和 EndUpdate 方法以高效的方式向 ComboBox 添加大量项。

[C#] 

using System;

using System.Windows.Forms;

namespace Win32Form1Namespace {

    public class Win32Form1 : System.Windows.Forms.Form {

        private System.Windows.Forms.Button addButton;

        private System.Windows.Forms.TextBox textBox2;

        private System.Windows.Forms.Button addGrandButton;

        private System.Windows.Forms.ComboBox comboBox1;

        private System.Windows.Forms.Button showSelectedButton;

        private System.Windows.Forms.TextBox textBox1;

        private System.Windows.Forms.Button findButton;

        private System.Windows.Forms.Label label1;

        public Win32Form1() {

            this.InitializeComponent();

        }

        [System.STAThreadAttribute()]

        public static void Main() {

            System.Windows.Forms.Application.Run(new Win32Form1());

        }

        private void InitializeComponent() {

            this.addButton = new System.Windows.Forms.Button();

            this.textBox2 = new System.Windows.Forms.TextBox();

            this.addGrandButton = new System.Windows.Forms.Button();

            this.comboBox1 = new System.Windows.Forms.ComboBox();

            this.showSelectedButton = new System.Windows.Forms.Button();

            this.textBox1 = new System.Windows.Forms.TextBox();

            this.findButton = new System.Windows.Forms.Button();

            this.label1 = new System.Windows.Forms.Label();

            this.addButton.Location = new System.Drawing.Point(248, 32);

            this.addButton.Size = new System.Drawing.Size(40, 24);

            this.addButton.TabIndex = 1;

            this.addButton.Text = "Add";

            this.addButton.Click += new System.EventHandler(this.addButton_Click);

            this.textBox2.Location = new System.Drawing.Point(8, 64);

            this.textBox2.Size = new System.Drawing.Size(232, 20);

            this.textBox2.TabIndex = 6;

            this.textBox2.Text = "";

            this.addGrandButton.Location = new System.Drawing.Point(8, 96);

            this.addGrandButton.Size = new System.Drawing.Size(280, 23);

            this.addGrandButton.TabIndex = 2;

            this.addGrandButton.Text = "Add 1,000 Items";

            this.addGrandButton.Click += new System.EventHandler(this.addGrandButton_Click);

            this.comboBox1.Anchor = ((System.Windows.Forms.AnchorStyles.Bottom | System.Windows.Forms.AnchorStyles.Left) 

                        | System.Windows.Forms.AnchorStyles.Right);

            this.comboBox1.DropDownWidth = 280;

            this.comboBox1.Items.AddRange(new object[] {"Item 1",

                        "Item 2",

                        "Item 3",

                        "Item 4",

                        "Item 5"});

            this.comboBox1.Location = new System.Drawing.Point(8, 248);

            this.comboBox1.Size = new System.Drawing.Size(280, 21);

            this.comboBox1.TabIndex = 7;

            this.showSelectedButton.Location = new System.Drawing.Point(8, 128);

            this.showSelectedButton.Size = new System.Drawing.Size(280, 24);

            this.showSelectedButton.TabIndex = 4;

            this.showSelectedButton.Text = "What Item is Selected?";

            this.showSelectedButton.Click += new System.EventHandler(this.showSelectedButton_Click);

            this.textBox1.Location = new System.Drawing.Point(8, 32);

            this.textBox1.Size = new System.Drawing.Size(232, 20);

            this.textBox1.TabIndex = 5;

            this.textBox1.Text = "";

            this.findButton.Location = new System.Drawing.Point(248, 64);

            this.findButton.Size = new System.Drawing.Size(40, 24);

            this.findButton.TabIndex = 3;

            this.findButton.Text = "Find";

            this.findButton.Click += new System.EventHandler(this.findButton_Click);

            this.label1.Location = new System.Drawing.Point(8, 224);

            this.label1.Size = new System.Drawing.Size(144, 23);

            this.label1.TabIndex = 0;

            this.label1.Text = "Test ComboBox";

            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);

            this.ClientSize = new System.Drawing.Size(292, 273);

            this.Controls.AddRange(new System.Windows.Forms.Control[] {this.comboBox1,

                        this.textBox2,

                        this.textBox1,

                        this.showSelectedButton,

                        this.findButton,

                        this.addGrandButton,

                        this.addButton,

                        this.label1});

            this.Text = "ComboBox Sample";

        }

        private void addButton_Click(object sender, System.EventArgs e) {

           comboBox1.Items.Add(textBox1.Text);

        }

        private void addGrandButton_Click(object sender, System.EventArgs e) {

            comboBox1.BeginUpdate();

            for (int i = 0; i < 1000; i++) {

                comboBox1.Items.Add("Item 1" + i.ToString());

            }

            comboBox1.EndUpdate();

        }

        private void findButton_Click(object sender, System.EventArgs e) {

            int index = comboBox1.FindString(textBox2.Text);

            comboBox1.SelectedIndex = index;

        }

        private void showSelectedButton_Click(object sender, System.EventArgs e) {

            int selectedIndex = comboBox1.SelectedIndex;

            Object selectedItem = comboBox1.SelectedItem;

            MessageBox.Show("Selected Item Text: " + selectedItem.ToString() + "/n" +

                            "Index: " + selectedIndex.ToString());

        }

    }

}