meta-data在清单文件中主要有以下用法：
<application>
<meta-data android:value="a1" android:name="a1"></meta-data>
</application>
//<application>用法
ApplicationInfo appInfo = this.getPackageManager().getApplicationInfo(getPackageName(),PackageManager.GET_META_DATA);
String msg=appInfo.metaData.getString("a1");
<activity>
<meta-data android:name="a2" android:value="a2"></meta-data>
</activity>
ActivityInfo info=this.getPackageManager().getActivityInfo(getComponentName(),PackageManager.GET_META_DATA);
String msg=info.metaData.getString("a2");
<service>
<meta-data android:value="a3" android:name="a3"></meta-data>
</service>
ComponentName cn=new ComponentName(this, MetaDataService.class);
ServiceInfo info=this.getPackageManager().getServiceInfo(cn, PackageManager.GET_META_DATA);
String msg=info.metaData.getString("a3");
<receiver android:name="MetaDataReceiver">
<meta-data android:value="a4" android:name="a4"></meta-data>
</receiver>
ComponentName cn=new ComponentName(context, MetaDataReceiver.class);
ReceiverInfo info=context.getPackageManager().getReceiverInfo(cn, PackageManager.GET_META_DATA);
String msg=info.metaData.getString("a4");