/// <summary>/// 定义将属性扩展到容器中的其他组件的接口。/// </summary>public interface IExtenderProvider{/// <summary>/// 指定此对象是否可以将其扩展程序属性提供给指定的对象。/// </summary>/// <param name="extendee">要接收扩展程序属性的System.Object。</param>/// <returns>如果此对象可以扩展程序属性提供给指定对象，则为true；否则为false。</returns>bool CanExtend(object extendee);}

    public class TextBoxEx:TextBox{protected override void OnDragLeave(EventArgs e){if (this.allowInput){if(this.Text.Trim().Length ==0){MessageBox.Show("文本框必须输入字符！", "提示", MessageBoxButtons.OK, 

                      MessageBoxIcon.Information);if (this.CanFocus)this.Focus();}base.OnDragLeave(e);}}/// <summary>/// 是否容器输入为空。/// </summary>[Category("验证")][Description("获取/设置是否必须输入")][DefaultValue(false)][Browsable(true)]public bool AllowInput{get{return this.allowInput;}set{this.allowInput = value;}}/// <summary>/// 默认必须输入字符。/// </summary>private bool allowInput = false;}

    [ToolboxItem(true)][Description("TextBox必须输入组件。")][ProvideProperty("AllowInput", typeof(TextBox))]public partial class TextBoxAllowInput : Component, System.ComponentModel.IExtenderProvider{private Dictionary<TextBox, bool> allowInputList = null;public TextBoxAllowInput(){InitializeComponent();allowInputList = new Dictionary<TextBox, bool>();}public TextBoxAllowInput(IContainer container){container.Add(this);InitializeComponent();allowInputList = new Dictionary<TextBox, bool>();}[Category("输入验证")][Description("获取/设置文本框是否必须输入")]public bool GetAllowInput(TextBox textBox){if (allowInputList.ContainsKey(textBox)){return (bool)allowInputList[textBox];}return false;}public void SetAllowInput(TextBox textBox, bool allowInput){if (!allowInputList.ContainsKey(textBox)){allowInputList.Add(textBox, allowInput);textBox.Leave += new EventHandler(textBox_Leave); }else{allowInputList[textBox] = allowInput;}}void textBox_Leave(object sender, EventArgs e){TextBox tb = sender as TextBox;if (this.GetAllowInput(tb)){if (tb.Text.Trim().Length == 0){MessageBox.Show("文本框必须输入字符！", "提示", MessageBoxButtons.OK, 

                      MessageBoxIcon.Information);if (tb.CanFocus)tb.Focus();}}}        public bool CanExtend(object extendee){return (extendee is TextBox); //只扩展TextBox}}