WinForm IP地址输入框控件实现

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;
using System.Text.RegularExpressions;

namespace IPInputControl.Ctrl
{
 public partial class IPInput : UserControl
 {
 public IPInput()
 {
  InitializeComponent();
 }
 TextBox ParentTxt;
 private void IPInput_Load(object sender, EventArgs e)
 {
  ParentTxt = txt_1;
 }
 public void txt_KeyDown(object sender, KeyEventArgs e)
 {
  ParentTxt = (TextBox)sender;
  if (e.KeyCode == Keys.Left)
  {
  switch (ParentTxt.Name.Split('_')[1])
  {
   case "1":
   break;
   case "2":
   if (ParentTxt.SelectionStart == 0 && ParentTxt.Text != "")
   {
    if (int.Parse(ParentTxt.Text) > 255)
    {
    MessageBox.Show(ParentTxt.Text + "不是有效项。请指定一个介于1和255之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    ParentTxt.Text = "255";
    ParentTxt.SelectionStart = 0;
    }
    else
    {
    txt_1.Focus();
    }
   }
   else if (ParentTxt.Text == "")
   {
    txt_1.Focus();
   }
   break;
   case "3":
   if (ParentTxt.SelectionStart == 0 && ParentTxt.Text != "")
   {
    if (int.Parse(ParentTxt.Text) > 255)
    {
    MessageBox.Show(ParentTxt.Text + "不是有效项。请指定一个介于1和255之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    ParentTxt.Text = "255";
    ParentTxt.SelectionStart = 0;
    }
    else
    {
    txt_2.Focus();
    }
   }
   else if (ParentTxt.Text == "")
   {
    txt_2.Focus();
   }
   break;
   case "4":
   if (ParentTxt.SelectionStart == 0 && ParentTxt.Text != "")
   {
    if (int.Parse(ParentTxt.Text) > 255)
    {
    MessageBox.Show(ParentTxt.Text + "不是有效项。请指定一个介于1和255之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    ParentTxt.Text = "255";
    ParentTxt.SelectionStart = 0;
    }
    else
    {
    txt_3.Focus();
    }
   }
   else if (ParentTxt.Text == "")
   {
    txt_3.Focus();
   }
   break;
  }
  }
  else if (e.KeyCode == Keys.Right)
  {
  switch (ParentTxt.Name.Split('_')[1])
  {
   case "1":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length && ParentTxt.Text != "")
   {
    if (int.Parse(ParentTxt.Text) > 223)
    {
    MessageBox.Show(ParentTxt.Text + "不是有效项。请指定一个介于1和223之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    ParentTxt.Text = "223";
    ParentTxt.SelectionStart = ParentTxt.Text.Length;
    }
    else
    {
    txt_2.Focus();
    }
   }
   else if (ParentTxt.Text == "")
   {
    txt_2.Focus();
   }
   break;
   case "2":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length && ParentTxt.Text != "")
   {
    if (int.Parse(ParentTxt.Text) > 255)
    {
    MessageBox.Show(ParentTxt.Text + "不是有效项。请指定一个介于1和255之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    ParentTxt.Text = "255";
    ParentTxt.SelectionStart = ParentTxt.Text.Length;
    }
    else
    {
    txt_3.Focus();
    }
   }
   else if (ParentTxt.Text == "")
   {
    txt_3.Focus();
   }
   break;
   case "3":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length && ParentTxt.Text != "")
   {
    if (int.Parse(ParentTxt.Text) > 255)
    {
    MessageBox.Show(ParentTxt.Text + "不是有效项。请指定一个介于1和255之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    ParentTxt.Text = "255";
    ParentTxt.SelectionStart = ParentTxt.Text.Length;
    }
    else
    {
    txt_4.Focus();
    }
   }
   else if (ParentTxt.Text == "")
   {
    txt_4.Focus();
   }
   break;
   case "4":
   break;
  }
  }
 }
 public void txt_KeyPress(object sender, KeyPressEventArgs e)
 {
  ParentTxt = (TextBox)sender;
  Regex regex = new Regex(@"^[0-9]+$");
  if (!regex.IsMatch(e.KeyChar.ToString()) && e.KeyChar != (Char)Keys.Back)
  {
  e.Handled = true;
  }
  else if (e.KeyChar == (Char)Keys.Back)
  {
  e.Handled = false;
  switch (ParentTxt.Name.Split('_')[1])
  {
   case "1":
   break;
   case "2":
   if (ParentTxt.SelectionStart == 0)
   {
    txt_1.Focus();
    if (txt_1.Text != "")
    {
    txt_1.Text = txt_1.Text.Substring(0, txt_1.Text.Length - 1);
    }
    txt_1.SelectionStart = txt_1.Text.Length;
   }
   break;
   case "3":
   if (ParentTxt.SelectionStart == 0)
   {
    txt_2.Focus();
    if (txt_2.Text != "")
    {
    txt_2.Text = txt_2.Text.Substring(0, txt_2.Text.Length - 1);
    }
    txt_2.SelectionStart = txt_2.Text.Length;
   }
   break;
   case "4":
   if (ParentTxt.SelectionStart == 0)
   {
    txt_3.Focus();
    if (txt_3.Text != "")
    {
    txt_3.Text = txt_3.Text.Substring(0, txt_3.Text.Length - 1);
    }
    txt_3.SelectionStart = txt_3.Text.Length;
   }
   break;
  }
  }
  else
  {
  switch (ParentTxt.Name.Split('_')[1])
  {
   case "1":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length)
   {
    if (int.Parse(ParentTxt.Text + e.KeyChar.ToString()) > 223)
    {
    MessageBox.Show(ParentTxt.Text + e.KeyChar.ToString() + "不是有效项。请指定一个介于1和223之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    e.Handled = true;
    ParentTxt.Text = "223";
    }
    else
    {
    e.Handled = false;
    }
   }
   else if(ParentTxt.Text.Length != 3)
   {
    e.Handled = false;
   }
   else
   {
    e.Handled = true;
   }
   break;
   default:
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length)
   {
    if (int.Parse(ParentTxt.Text + e.KeyChar.ToString()) > 255)
    {
    MessageBox.Show(ParentTxt.Text + e.KeyChar.ToString() + "不是有效项。请指定一个介于1和255之间的值。", "错误", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    e.Handled = true;
    ParentTxt.Text = "255";
    }
    else
    {
    e.Handled = false;
    }
   }
   else if (ParentTxt.Text.Length != 3)
   {
    e.Handled = false;
   }
   else
   {
    e.Handled = true;
   }
   break;
  }
  }
 }
 public void txt_TextChanged(object sender, EventArgs e)
 {
  if (ParentTxt.Text.Length == 3)
  {
  switch (ParentTxt.Name.Split('_')[1])
  {
   case "1":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length)
   {
    txt_2.Focus();
   }
   break;
   case "2":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length)
   {
    txt_3.Focus();
   }
   break;
   case "3":
   if (ParentTxt.SelectionStart == ParentTxt.Text.Length)
   {
    txt_4.Focus();
   }
   break;
   case "4":
   break;
  }
  }
 }
 }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;
using System.Text.RegularExpressions;

namespace IPInputControl.Ctrl
{
 public partial class ControlText : TextBox
 {
 public ControlText()
 {
  InitializeComponent();
 }
 public void txt_TextChange(object sender, EventArgs e)
 {
  if (this.Text.Length == 3)
  {
  SendKeys.Send("{TAB}");
  }
 }
 protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
 {
  if (keyData == Keys.Tab)
  {
  return true;
  }
  return base.ProcessCmdKey(ref msg, keyData);
 }
 }
}