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

Question

Displaying "Type here to ..." until the user enters text into a TextBox is a well-known usability feature nowadays. How would one implement this feature in C#?

My idea is to override OnTextChanged, but the logic to handle the changes of text from and to "Type here" is a bit tricky...

Displaying "Type here" on initialization and removing it on first input is easy, but I want to display the message every time the entered text becomes empty.

Answer 1

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.