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;
  }