Question

I am creating a C# WinForms application in VS 2010. I have 10 TextBoxes.

For TextBox1, I handled the events for GotFocus, LostFocus, etc. in the following manner:

this.richTextBox1.GotFocus += new System.EventHandler(this.RichTextBox1_GotFocus);
this.richTextBox1.LostFocus += new System.EventHandler(this.RichTextBox1_LostFocus);

private void TextBox1_GotFocus(object sender, System.EventArgs e)
{
    TextBox1.BackColor = Color.White;
}

private void TextBox1_LostFocus(object sender, System.EventArgs e)
{
    TextBox1.BackColor = Color.LightSteelBlue;
}

And now I need to write the same code for all of my textboxes. Is it instead possible to have a common GotFocus, LostFocus, etc. event handler method for all textboxes to do the above things?

Answer 1

If you really need this for 10 different textboxes, the best (and most object-oriented) thing to do would be to create your own custom textbox control that inherits from System.Windows.Forms.TextBox.

Since you’re inheriting from the base TextBox class, you get all of its functionality for free, and you can also implement the custom behavior that you want. Then just use this custom control as a drop-in replacement for the standard textbox control wherever you want controls with this behavior on your form. This way, you don’t have to attach any event handlers at all! The behavior is built right into your control, following the guidelines of encapsulation and don’t-repeat-yourself.

Sample class:

public class FocusChangeTextBox : TextBox
{
    public FocusChangeTextBox()
    {
    }

    protected override void OnGotFocus(EventArgs e)
    {
        // Call the base class implementation
        base.OnGotFocus();

        // Implement your own custom behavior
        this.BackColor = SystemColors.Window;
    }

    protected override void OnLostFocus(EventArgs e)
    {
        // Call the base class implementation
        base.OnLostFocus();

        // Implement your own custom behavior
        this.BackColor = Color.LightSteelBlue;
    }
}