EditText et_content;//定义一个文本输入框
TextView tv_num;// 用来显示剩余字数
int num = 10;//限制的最大字数

et_content = (EditText) findViewById(R.id.et_content);
tv_num = (TextView) findViewById(R.id.tv_num);
tv_num.setText("10");

et_content.addTextChangedListener(new TextWatcher() {
  private CharSequence temp;
  private int selectionStart;
  private int selectionEnd;
  @Override
  public void onTextChanged(CharSequence s, int start, int before,
      int count) {
    temp = s;
    System.out.println("s="+s);
  }
  @Override
  public void beforeTextChanged(CharSequence s, int start, int count,
      int after) {
  }
  @Override
  public void afterTextChanged(Editable s) {
    int number = num - s.length();
    tv_num.setText("" + number);
    selectionStart = et_content.getSelectionStart();
    selectionEnd = et_content.getSelectionEnd();
    //System.out.println("start="+selectionStart+",end="+selectionEnd);
    if (temp.length() > num) {
      s.delete(selectionStart - 1, selectionEnd);
      int tempSelection = selectionStart;
      et_content.setText(s);
      et_content.setSelection(tempSelection);//设置光标在最后
    }
  }
});