对EditText输入字数限制并提示

private int num = 500;//详情描述限制的最大字数

etDetailDescription.addTextChangedListener(new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        Editable editable = etDetailDescription.getText();
        int len = editable.length();

        if (len > num) {
            showToast("超出字数限制");
            int selEndIndex = Selection.getSelectionEnd(editable);
            String str = editable.toString();
            //截取新字符串
            String newStr = str.substring(0, num);
            etDetailDescription.setText(newStr);
            editable = etDetailDescription.getText();

            //新字符串的长度
            int newLen = editable.length();
            //旧光标位置超过字符串长度
            if (selEndIndex > newLen) {
                selEndIndex = editable.length();
            }
            //设置新光标所在的位置
            Selection.setSelection(editable, selEndIndex);
        }
    }

    @Override
    public void afterTextChanged(Editable s) {
    }
});