Winform控件扩展

1.TextBox 增加水印

新增一个用户控件，将继承UserControl改为TextBox

public partial class TextBoxEP : TextBox
    {
        public TextBoxEP()
        {
            InitializeComponent();
        }

        private const uint WT_Mark = 0x1501;

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, uint wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);

        private string watermarkText;

        [Description("水印文字")]
        public string WatermarkText
        {
            get { return watermarkText; }
            set
            {
                watermarkText = value;
                SetWatermark(watermarkText);
            }
        }

        private void SetWatermark(string watermarkText)
        {
            SendMessage(this.Handle, WT_Mark, 0, watermarkText);
        }
    }