[WinForm]为TextBox设置水印文字

关键代码：

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);

        }

    }

}

测试代码：

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();

        }

    }

}

测试效果：

希望有所帮助！