Winform 水印TextBox(近乎完美)

public partial class WaterTextBox : TextBox

{

    private readonly Label lblwaterText = new Label();



    public WaterTextBox()

    {

        InitializeComponent();

        lblwaterText.BorderStyle = BorderStyle.None;

        lblwaterText.Enabled = false;

        lblwaterText.BackColor = Color.White;

        lblwaterText.AutoSize = false;

        lblwaterText.Top = 1;

        lblwaterText.Left = 2;

        lblwaterText.FlatStyle = FlatStyle.System;

        Controls.Add(lblwaterText);

    }



    [Category("扩展属性"), Description("显示的提示信息")]

    public string WaterText

    {

        get { return lblwaterText.Text; }

        set { lblwaterText.Text = value; }

    }



    public override string Text

    {

        set

        {

            lblwaterText.Visible = value == string.Empty;

            base.Text = value;

        }

        get

        {

            return base.Text;

        }

    }



    protected override void OnSizeChanged(EventArgs e)

    {

        if (Multiline && (ScrollBars == ScrollBars.Vertical || ScrollBars == ScrollBars.Both))

            lblwaterText.Width = Width - 20;

        else

            lblwaterText.Width = Width;

        lblwaterText.Height = Height - 2;

        base.OnSizeChanged(e);

    }



    protected override void OnTextChanged(EventArgs e)

    {

        lblwaterText.Visible = base.Text == string.Empty;

        base.OnTextChanged(e);

    }



    protected override void OnMouseDown(MouseEventArgs e)

    {

        lblwaterText.Visible = false;

        base.OnMouseDown(e);

    }



    protected override void OnMouseLeave(EventArgs e)

    {

        lblwaterText.Visible = base.Text == string.Empty;

        base.OnMouseLeave(e);

    }



    //protected override void OnEnter(EventArgs e)

    //{

    //    lblwaterText.Visible = false;

    //    base.OnEnter(e);

    //}



    //protected override void OnLeave(EventArgs e)

    //{

    //    if (string.IsNullOrEmpty(base.Text))

    //        lblwaterText.Visible = true;

    //    base.OnLeave(e);

    //}

}

新加一种方法（转）：

 public partial class PromptTextBox : TextBox
    {
        private string promptString = string.Empty;
        private bool IsEmpty = true;
        public PromptTextBox()
        {
            InitializeComponent();
        }
        public PromptTextBox(string prompt)
        {
            InitializeComponent();
            PromptString = prompt;
        }
        /**/
        /// <summary>
        /// Prompt Text
        /// </summary>
        public string PromptString
        {
            get { return promptString; }
            set { promptString = value; }
        }
        protected override void OnEnter(EventArgs e)
        {
            if (IsEmpty) { Clear(); }
        }
        protected override void OnLeave(EventArgs e)
        {
            if (Text == string.Empty)
            {
                Text = PromptString;
                IsEmpty = true;
            }
            else { IsEmpty = false; }
        }
        public override string Text
        {
            get
            {
                if (IsEmpty) { return string.Empty; }
                else { return base.Text; }
            }
            set
            {
                if (value == string.Empty)
                {
                    base.Text = PromptString;
                    IsEmpty = true;
                }
                else
                {
                    IsEmpty = (value == PromptString);
                    base.Text = value;
                }
            }
        }
        protected override void OnCreateControl()
        {
            if (Text == string.Empty)
            {
                Text = PromptString;
                IsEmpty = true;
            }
            else { IsEmpty = false; }
        }
    }