using System;

using System.Runtime.InteropServices;

using System.Windows.Forms;

namespace WinFormUtilHelpV2

{

  /// <summary>

  /// 基于.NET 2.0的TextBox工具类

  /// </summary>

  public static class TextBoxToolV2

  {

    private const int EM_SETCUEBANNER = 0x1501;

    [DllImport("user32.dll", CharSet = CharSet.Auto)]

    private static extern Int32 SendMessage

     (IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);

    /// <summary>

    /// 为TextBox设置水印文字

    /// </summary>

    /// <param name="textBox">TextBox</param>

    /// <param name="watermark">水印文字</param>

    public static void SetWatermark(this TextBox textBox, string watermark)

    {

      SendMessage(textBox.Handle, EM_SETCUEBANNER, 0, watermark);

    }

    /// <summary>

    /// 清除水印文字

    /// </summary>

    /// <param name="textBox">TextBox</param>

    public static void ClearWatermark(this TextBox textBox)

    {

      SendMessage(textBox.Handle, EM_SETCUEBANNER, 0, string.Empty);

    }

  }

}

using System;

using System.Windows.Forms;

using WinFormUtilHelpV2;

namespace WinFormUtilHelpV2Test

{

  public partial class WinTextBoxToolV2Test : Form

  {

    public WinTextBoxToolV2Test()

    {

      InitializeComponent();

    }

    private void WinTextBoxToolV2Test_Load(object sender, EventArgs e)

    {

      textBox1.SetWatermark("请输入用户名称....");

      textBox2.SetWatermark("请输入用户密码....");

    }

    private void button1_Click(object sender, EventArgs e)

    {

      textBox1.ClearWatermark();

      textBox2.ClearWatermark();

    }

  }

}