Question

I have a Form with a TextBox. I would like to prevent the user from moving on to the next form without filling in the black TextBox. How can I do that?

if(textBox.Text.Length == 0)
    MessageBox.Show("Have To Fill All The Fields!");

What more should I add?

Answer 1

Add handler to Validating event and use error provider to set validation error to control:

void textBox_Validating(object sender, CancelEventArgs e) 
{
  string error = null;
  if(textBox.Text.Length == 0 ) {
    error = "Please enter this value";
    e.Cancel = true;
  }
  errorProvider1.SetError((Control)sender, error);
}

You can use same handler for several textbox controls (just use sender from event arguments to get particular textbox instance).