How do I implement a TextBox that displays "Type here"?

Based on @Pooven's answer (thank you!), I created this class. Works for me.

/// <summary>
/// A textbox that supports a watermak hint.
/// </summary>
public class WatermarkTextBox : TextBox
{
    /// <summary>
    /// The text that will be presented as the watermak hint
    /// </summary>
    private string _watermarkText = "Type here";
    /// <summary>
    /// Gets or Sets the text that will be presented as the watermak hint
    /// </summary>
    public string WatermarkText
    {
        get { return _watermarkText; }
        set { _watermarkText = value; }
    }

    /// <summary>
    /// Whether watermark effect is enabled or not
    /// </summary>
    private bool _watermarkActive = true;
    /// <summary>
    /// Gets or Sets whether watermark effect is enabled or not
    /// </summary>
    public bool WatermarkActive
    {
        get { return _watermarkActive; }
        set { _watermarkActive = value; }
    }

    /// <summary>
    /// Create a new TextBox that supports watermak hint
    /// </summary>
    public WatermarkTextBox()
    {
        this._watermarkActive = true;
        this.Text = _watermarkText;
        this.ForeColor = Color.Gray;

        GotFocus += (source, e) =>
        {
            RemoveWatermak();
        };

        LostFocus += (source, e) =>
        {
            ApplyWatermark();
        };

    }

    /// <summary>
    /// Remove watermark from the textbox
    /// </summary>
    public void RemoveWatermak()
    {
        if (this._watermarkActive)
        {
            this._watermarkActive = false;
            this.Text = "";
            this.ForeColor = Color.Black;
        }
    }

    /// <summary>
    /// Applywatermak immediately
    /// </summary>
    public void ApplyWatermark()
    {
        if (!this._watermarkActive && string.IsNullOrEmpty(this.Text)
            || ForeColor == Color.Gray ) 
        {
            this._watermarkActive = true;
            this.Text = _watermarkText;
            this.ForeColor = Color.Gray;
        }
    }

    /// <summary>
    /// Apply watermak to the textbox. 
    /// </summary>
    /// <param name="newText">Text to apply</param>
    public void ApplyWatermark(string newText)
    {
        WatermarkText = newText;
        ApplyWatermark();
    }

}

What you're looking for is a TextBox with a "watermark".

There's a sample implementation for C# here, all credits to Wael Alghool.

The relevant part of his code is:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;

namespace wmgCMS
{
    class WaterMarkTextBox : TextBox
    {
        private Font oldFont = null;
        private Boolean waterMarkTextEnabled = false;

        #region Attributes 
            private Color _waterMarkColor = Color.Gray;
            public Color WaterMarkColor
            {
                get { return _waterMarkColor; }
                set { _waterMarkColor = value; Invalidate();/*thanks to Bernhard Elbl
                                                              for Invalidate()*/ }
            }

            private string _waterMarkText = "Water Mark";
            public string WaterMarkText
            {
                get { return _waterMarkText; }
                set { _waterMarkText = value; Invalidate(); }
            }
        #endregion

        //Default constructor
        public WaterMarkTextBox()
        {
            JoinEvents(true);
        }

        //Override OnCreateControl ... thanks to  "lpgray .. codeproject guy"
        protected override void OnCreateControl() 
        { 
            base.OnCreateControl();
            WaterMark_Toggel(null, null); 
        }

        //Override OnPaint
        protected override void OnPaint(PaintEventArgs args)
        {
            // Use the same font that was defined in base class
            System.Drawing.Font drawFont = new System.Drawing.Font(Font.FontFamily,
                Font.Size, Font.Style, Font.Unit);
            //Create new brush with gray color or 
            SolidBrush drawBrush = new SolidBrush(WaterMarkColor);//use Water mark color
            //Draw Text or WaterMark
            args.Graphics.DrawString((waterMarkTextEnabled ? WaterMarkText : Text),
                drawFont, drawBrush, new PointF(0.0F, 0.0F));
            base.OnPaint(args);
        }

        private void JoinEvents(Boolean join)
        {
            if (join)
            {
                this.TextChanged += new System.EventHandler(this.WaterMark_Toggel);
                this.LostFocus += new System.EventHandler(this.WaterMark_Toggel);
                this.FontChanged += new System.EventHandler(this.WaterMark_FontChanged);
                //No one of the above events will start immeddiatlly 
                //TextBox control still in constructing, so,
                //Font object (for example) couldn't be catched from within
                //WaterMark_Toggle
                //So, call WaterMark_Toggel through OnCreateControl after TextBox
                //is totally created
                //No doupt, it will be only one time call

                //Old solution uses Timer.Tick event to check Create property
            }
        }

        private void WaterMark_Toggel(object sender, EventArgs args )
        {
            if (this.Text.Length <= 0)
                EnableWaterMark();
            else
                DisbaleWaterMark();
        }

        private void EnableWaterMark()
        {
            //Save current font until returning the UserPaint style to false (NOTE:
            //It is a try and error advice)
            oldFont = new System.Drawing.Font(Font.FontFamily, Font.Size, Font.Style,
               Font.Unit);
            //Enable OnPaint event handler
            this.SetStyle(ControlStyles.UserPaint, true);
            this.waterMarkTextEnabled = true;
            //Triger OnPaint immediatly
            Refresh();
        }

        private void DisbaleWaterMark()
        {
            //Disbale OnPaint event handler
            this.waterMarkTextEnabled = false;
            this.SetStyle(ControlStyles.UserPaint, false);
            //Return back oldFont if existed
            if(oldFont != null)
                this.Font = new System.Drawing.Font(oldFont.FontFamily, oldFont.Size,
                    oldFont.Style, oldFont.Unit);
        }

        private void WaterMark_FontChanged(object sender, EventArgs args)
        {
            if (waterMarkTextEnabled)
            {
                oldFont = new System.Drawing.Font(Font.FontFamily,Font.Size,Font.Style,
                    Font.Unit);
                Refresh();
            }
        }
    }
}

Something that has worked for me:

this.waterMarkActive = true;
this.textBox.ForeColor = Color.Gray;
this.textBox.Text = "Type here";

this.textBox.GotFocus += (source, e) =>
  {
    if (this.waterMarkActive)
    {
      this.waterMarkActive = false;
      this.textBox.Text = "";
      this.textBox.ForeColor = Color.Black;
    }
  };

this.textBox.LostFocus += (source, e) =>
  {
    if (!this.waterMarkActive && string.IsNullOrEmpty(this.textBox.Text))
    {
      this.waterMarkActive = true;
      this.textBox.Text = "Type here";
      this.textBox.ForeColor = Color.Gray;
    }
  };

Where bool waterMarkActive is a class member variable and textBox is the TextBox. This probably should be encapsulated though :) There might be some issues with this approach, but I'm not currently aware of any.

I recently discovered that Windows support water marks in text boxes; they are called cue banners (see here). It's very easy to implement:

// Within your class or scoped in a more appropriate location:
[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);

// In your constructor or somewhere more suitable:
SendMessage(textBox.Handle, 0x1501, 1, "Please type here.");

Where textBox is an instance of TextBox, 0x1501 is the code for the windows message EM_SETCUEBANNER, the wParam may either be TRUE (non-zero) or FALSE (zero), and lParam is the water mark you'd like to display. wParam indicates when the cue banner should be displayed; if set to TRUE then the cue banner will be displayed even when the control has focus.