android EditText 字数监听并显示

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
}
}
});