自定义控件中只放了一个TextBox控件，并在TextBox下利用自定义控件的Paint画了一条线，然后给TextBox做了3个自定义属性，分别是TextBoxText属性，方便取值；IntBool属性，是否只输入正整数；inputDecimal是否只能输入小数。

以下是整个自定义控件的源代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Text.RegularExpressions;namespace GCIMS.CommonCtrl
{public partial class ctrlUnderlineTextBox : UserControl{#region 属性/// <summary>/// 控件的文本/// </summary>[Description("文本值"), Browsable(true), Category("自定义属性")]public string TextBoxText{get{return textBox.Text;}set{textBox.Text = value;}}private bool intBool;/// <summary>/// 只输入正整数/// </summary>[Description("只输入正整数"), Browsable(true), Category("自定义属性"), DefaultValue(false)]public bool IntBool{get{return intBool;}set{intBool = value;if (intBool){textBox.KeyPress += new KeyPressEventHandler(IntBool_KeyPress);}}}private bool inputDecimal;/// <summary>/// 只输入小数/// </summary>[Description("只输入小数"), Browsable(true), Category("自定义属性"), DefaultValue(false)]public bool InputDecimal{get{return inputDecimal;}set{inputDecimal = value;if (inputDecimal){textBox.KeyPress += new KeyPressEventHandler(InputDecimal_KeyPress);}}}#endregion#region 构造函数public ctrlUnderlineTextBox(){InitializeComponent();}#endregion#region 事件-ctrlUnderlineTextBox_KeyPressprivate void IntBool_KeyPress(object sender, KeyPressEventArgs e){if ((int)e.KeyChar >= 48 && (int)e.KeyChar <= 57 && textBox.Text.Length < 18 || (int)e.KeyChar == 8) //只能输入0-9数字和BackSpace{e.Handled = false;}else{e.Handled = true;}}#endregion#region 事件-InputDecimal_KeyPressprivate void InputDecimal_KeyPress(object sender, KeyPressEventArgs e){//搜索字符串中的'.'字符string textBoxStr = textBox.Text;Regex rg = new Regex(".");MatchCollection mc = rg.Matches(textBoxStr);int textBoxCount = mc.Count;//允许输入数字，小数点，退格键，不允许输入大于18为的数字，不允许输入两个小数点if ((int)e.KeyChar >= 48 && (int)e.KeyChar <= 57 && textBox.Text.Length < 18 || (int)e.KeyChar == 8 || e.KeyChar == '.' && textBoxCount <= 1) //只能输入0-9数字和BackSpace{e.Handled = false;}else{e.Handled = true;}}#endregion#region 事件-CtrlUnderlineTextBox_Paintprivate void CtrlUnderlineTextBox_Paint(object sender, PaintEventArgs e){Graphics g = Graphics.FromHwnd(this.Handle);System.Drawing.Pen pen = new Pen(Color.Black);PointF point1 = new PointF(textBox.Location.X, textBox.Location.Y + textBox.Height);PointF point2 = new PointF(textBox.Location.X + textBox.Width, textBox.Location.Y + textBox.Height);g.DrawLine(pen, point1, point2);}#endregion}
}