C# Winform 带水印提示输入框

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using System; using System.Drawing; using System.Runtime.InteropServices; using System.Windows.Forms;   namespace KK.WatermarkTextBox {     public partial class WatermarkTextBox : TextBox     {         private const uint ECM_FIRST = 0x1500;         private const uint EM_SETCUEBANNER = ECM_FIRST + 1;           [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]         static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, uint wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);           public WatermarkTextBox()         {             InitializeComponent();         }           private string watermarkText;         public string WatermarkText         {             get { return watermarkText; }             set             {                 watermarkText = value;                 SetWatermark(watermarkText);             }         }           private void SetWatermark(string watermarkText)         {             SendMessage(this.Handle, EM_SETCUEBANNER, 0, watermarkText);         }     } }

运行效果如下所示：