C# – Preventing a dialog from closing in the button’s click event handler

cnetwindowswinforms

I have a dialog that I show with <class>.ShowDialog(). It has an OK button and a Cancel button; the OK button also has an event handler.

I want to do some input validation in the event handler and, if it fails, notify the user with a message box and prevent the dialog from closing. I don't know how to do the last part (preventing the close).

Best Answer

You can cancel closing by setting the Form's DialogResult to DialogResult.None.

An example where button1 is the AcceptButton:

private void button1_Click(object sender, EventArgs e) {
  if (!validate())
     this.DialogResult = DialogResult.None;
}

When the user clicks button1 and the validate method returns false, the form will not be closed.

Related Solutions

R – How to handle a reentrant validation event when showing dialog

Take a look at the CausesValidation property on your controls. You can set whether or not a button you press causes your validation events to fire. You can also programatically set this to keep your validation logic from firing at inopportune times.

C# – How to update the GUI from another thread

The simplest way is an anonymous method passed into Label.Invoke:

// Running on the worker thread
string newText = "abc";
form.Label.Invoke((MethodInvoker)delegate {
    // Running on the UI thread
    form.Label.Text = newText;
});
// Back on the worker thread

Notice that Invoke blocks execution until it completes--this is synchronous code. The question doesn't ask about asynchronous code, but there is lots of content on Stack Overflow about writing asynchronous code when you want to learn about it.

Best Answer

Related Solutions

R – How to handle a reentrant validation event when showing dialog

C# – How to update the GUI from another thread

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