Monitor keystrokes

Question

I am a beginner in C# , and making a calculator . But i want to disable the "GO!" button when there's no number typed in textbox1 and once the user enters a number in it the "GO!" button becomes enabled again ... how to do this in C# ? i tried KeyDown and KeyPress event like this but never worked

private void Form1_Load(object sender, EventArgs e)
    {

            button15.Enabled = false;
         button16.Enabled = false;     

    }


 private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyEventArgs e)
    {

       if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
        {
            button15.Enabled = true;
            button16.Enabled = true;

        }
        else
        {
            button15.Enabled = false;
            button16.Enabled = false;
        }

    } 

so how to do this please ? thanks in advance .

Answer 1

private void textBox1_TextChanged(object sender, EventArgs e)
{
      if(String.IsNullOrEmpty(textBox1.Text))
      {
            button15.Enabled = false;
            button16.Enabled = false;
      }
      else
      {
            button15.Enabled = true;
            button16.Enabled = true;
      }
}