1.Exported receiver does not require permission
警告原因：该接收器或者服务是开放式的，需要内容添加权限属性
解决方案：
<receiver android:name="com.practice.app.receiver.SmsReceiver" android:permission="android.permission.RECEIVE_SMS">
2.<uses-permission> tag appears after <application> tag
警告原因：uses-permission 标签出现在 application后面
解决方案：将uses-permission 放到 application前面
3.<uses-sdk> tag should specify a target API level (the highest verified version; when running on later versions, compatibility
behaviors may be enabled) with android:targetSdkVersion="?"
警告原因：uses-sdk只设置了最低版本，没有设置目标版本
解决方案：设置目标版本
<uses-sdk android:minSdkVersion="6" android:targetSdkVersion="8" />