title: How to filter the input of EditText?
body: <p>I want to filter the input of an <code>EditText</code>, only digits and letters are allowed, first I use <code>TextWatcher</code> to deal with the last input character, but when you move the cursor or you past some content to the <code>EditText</code>, this method failed, now I want to know is there a way to filter the illegal input and give the user a feedback.</p>