Android TextWatcher监控EditText中的输入内容并限制其输入字符个数

布局中EditText在android布局中经常用到，对EditText中输入的内容也经常需要进行限制，我们可以通过TextWatcher去观察输入框中输入的内容

public class TextWatcherDemo extends Activity {
    private TextView mTextView;
    private EditText mEditText;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mTextView = (TextView)findViewById(R.id.tv);
        mEditText = (EditText)findViewById(R.id.ET);
        mEditText.addTextChangedListener(mTextWatcher);
    }
    TextWatcher mTextWatcher = new TextWatcher() {
        private CharSequence temp;
        private int editStart ;
        private int editEnd ;
        @Override
        public void beforeTextChanged(CharSequence s, int arg1, int arg2,
                int arg3) {
            temp = s;
        }
       
        @Override
        public void onTextChanged(CharSequence s, int arg1, int arg2,
                int arg3) {
            mTextView.setText(s);
        }
       
        @Override
        public void afterTextChanged(Editable s) {
            editStart = mEditText.getSelectionStart();
            editEnd = mEditText.getSelectionEnd();
            if (temp.length() > 10) {
                Toast.makeText(TextWatcherDemo.this,
                        "你输入的字数已经超过了限制！", Toast.LENGTH_SHORT)
                        .show();
                s.delete(editStart-1, editEnd);
                int tempSelection = editStart;
                mEditText.setText(s);
                mEditText.setSelection(tempSelection);
            }
        }
    };
}