title: To enable button if all the textfields are filled in ios
body: <p>I have designed a signup form in ios with four <code>UITextField</code>s and a <code>UIButton</code>. I have set the buttons' <code>enabled</code> property to <code>NO</code> by default. Now I want to enable the button only when all the four textfields are filled. Can you please help me out with this as I a new to ios, and stuck with this issue.</p>