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I have a Windows form that has a validation event on a textBox so that if the value of that TextBox is a value that already exists it triggers a validation error.

 private void txtUsername_Validating(object sender, CancelEventArgs e)
 
 var alreadyExists = _logic.UserIdExists(txtUsername.Text.Trim());

 if(alreadyExists)
 
 errorProvider1.SetError(txtUsername, "This Userid already exists, please choose an alternative");
 e.Cancel = true;
 
 

 private void txtUsername_Validated(object sender, EventArgs e)
 
 errorProvider1.SetError(txtUsername, "");
 


 this.txtUsername.Validating += new System.ComponentModel.CancelEventHandler(this.txtUsername_Validating);
 this.txtUsername.Validated += new System.EventHandler(this.txtUsername_Validated);

This results in an error image appearing next to that textBox along with a tooltip error message.

If I try and close the application, using the Close button at the top of the window, at this time I cannot as the above Event keeps firing even when I try and close the window (due to me taking focus away from the Text box).

Is there a way of closing the window, without resorting to creating an additional Close button on the form?

Based on your description, you want to maintain the default auto-validation behavior yet allow the Form to be closed using the title bar close button. I have observed that the Form.Closing event is raised in such a circumstance, however its argument Cancel property is preset to true. A simple solution is to handle this event and set e.Cancel = false. Implement any logic in the handler that you deem necessary.

private void Form1_FormClosing(object sender, FormClosingEventArgs e)

 if (e.CloseReason == CloseReason.UserClosing) e.Cancel = false;