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);
}
}
};
}

private TextWatcher mInputTextWatcher = new TextWatcher() {
private String temp;
private int editStart;
private int editEnd;
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
temp = s.toString();
}
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void afterTextChanged(Editable s) {
mMainHandler.removeMessages(HD_MSG_UPDATE_HINT);
mCurrentHint = s.toString().trim();
if (!TextUtils.isEmpty(temp)) {
String limitSubstring = getLimitSubstring(temp);
if (!TextUtils.isEmpty(limitSubstring)) {
if (!limitSubstring.equals(temp)) {
// Toast.makeText(activity, "字数已超过限制",
// Toast.LENGTH_SHORT).show();
mEdtInput.setText(limitSubstring);
mEdtInput.setSelection(limitSubstring.length());
}
}
}
mMainHandler.sendEmptyMessageDelayed(HD_MSG_UPDATE_HINT, HINT_UPDATE_DALEY_TIME);
}
};

private String getLimitSubstring(String inputStr) {
int orignLen = inputStr.length();
int resultLen = 0;
String temp = null;
for (int i = 0; i < orignLen; i++) {
temp = inputStr.substring(i, i + 1);
try {// 3 bytes to indicate chinese word,1 byte to indicate english
// word ,in utf-8 encode
if (temp.getBytes("utf-8").length == 3) {
resultLen += 2;
} else {
resultLen++;
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
if (resultLen > 30) {
return inputStr.substring(0, i);
}
}
return inputStr;
}