xm格式如下：

创建Button监听器

<Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/bt"
        android:onClick="backSms2"
        android:text="第二种方式短信的备份" />

private int id; // 短信的id

        /**  
	 * 第二种方式生成xml文件
	 * 
	 * @param view
	 */
	public void backSms2(View view) {
		try {
			XmlSerializer serializer = Xml.newSerializer(); // xml的序列化器
			File file = new File(Environment.getExternalStorageDirectory(),"backup2.xml");
			FileOutputStream fos = new FileOutputStream(file);
			serializer.setOutput(fos,"utf-8"); // 初始化序列号器，指定xml数据写入到哪个文件，并且指定文件的编码方式
			serializer.startDocument("utf-8",true); // 开头
			serializer.startTag(null,"smss");// 开始结点
			for (SmsInfo info : smsInfos) {
				serializer.startTag(null,"sms"); // sms开始
				serializer.attribute(null,"id",info.getId() + ""); // id
				// body
				serializer.startTag(null,"body");
				serializer.text(info.getBody());
				serializer.endTag(null,"body");
				// address
				serializer.startTag(null,"address");
				serializer.text(info.getAddress());
				serializer.endTag(null,"address");
				// type
				serializer.startTag(null,"type");
				serializer.text(info.getType() + "");
				serializer.endTag(null,"type");
				// date
				serializer.startTag(null,"date");
				serializer.text(info.getDate() + "");
				serializer.endTag(null,"date");

				serializer.endTag(null,"sms"); // sms结束
			}
			serializer.endTag(null,"smss"); // 结束结点
			serializer.endDocument(); // 结尾
			fos.close();
			Toast.makeText(this,"备份成功",Toast.LENGTH_SHORT).show();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			Toast.makeText(this,"备份失败",Toast.LENGTH_SHORT).show();
		}
	}