文本框\带输入提示的文本框

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);
        }
    }
}

using System.Drawing;
using System.Windows.Forms;
 
namespace KK.WaterMark.Control
{
    public partial class WaterMarkTextBox : TextBox
    {
        private string watermarkText;
        public string WatermarkText
        {
            get { return watermarkText; }
            set { watermarkText = value; }
        }
        private Color watermarkTextColor;
        public Color WatermarkTextColor
        {
            get { return watermarkTextColor; }
            set { watermarkTextColor = value; }
        }
 
        public WaterMarkTextBox()
        {
            InitializeComponent();
        }
 
        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
 
            if (m.Msg ==0x000F )//WM_PAINT
            {
                WmPaint(ref m);
            }
        }
 
        private void WmPaint(ref Message m)
        {
            Rectangle rectangle = new Rectangle(0, 0, Width, Height);
            using (Graphics graphics = Graphics.FromHwnd(base.Handle))
            {
                if (Text.Length == 0
                   && !string.IsNullOrEmpty(watermarkText)
                   && !Focused)
                {
                    TextFormatFlags format = TextFormatFlags.EndEllipsis
                        | TextFormatFlags.VerticalCenter;
 
                    if (RightToLeft == RightToLeft.Yes)
                    {
                        format |= TextFormatFlags.RightToLeft | TextFormatFlags.Right;
                    }
 
                    TextRenderer.DrawText(graphics, watermarkText, Font, 
                        base.ClientRectangle, watermarkTextColor, format);
                }
            }
        }
    }
}