C# WInforms Change border style on button click event

Question

I'm trying to change the border color of a text box (txtUser) on button click event (something like a form validation, if the input is empty then call the method that colors the border red). I did some googling and found this:

void myControl1_Paint(object sender, PaintEventArgs e)
{
ControlPaint.DrawBorder(e.Graphics, this.txtUser.ClientRectangle, Color.Black, ButtonBorderStyle.Solid);
}

But I'm having trouble understaing where or how should I call this method, or methods with (object sender, PaintEventArgs e) as params. Any explanation is appreciated.

Answer 1

You need to inherit from TextBox and then override the OnPaint method. Something like this should work:

public class ValidateEdit : TextBox
{
    bool _InError;

    public ValidateEdit()
    {
        SetStyle(ControlStyles.UserPaint, true);
    }

    public bool InError {
        get {
            return _InError;
        }
        set
        {
            _InError = value;
            Refresh();
        }
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        if (InError)
            ControlPaint.DrawBorder(e.Graphics, this.DisplayRectangle, Color.Red, ButtonBorderStyle.Solid);
    }
}