title: AlertDialog with positive button and validating custom EditText
body: <p>I have created simple <code>AlertDialog</code> with positive and negative buttons. Positive button has registered <code>DialogInterface.OnClickListener</code>, where I get <code>EditText</code> value. I have to validate it (for example if it has to be not null) and if value is not correct, disallow to close this dialog. How to prevent dismissing dialog after click and validate ?</p>