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Android 中 meta-data 用在 AndroidManifest.xml 文件中。<meta-data>标签是提供组件额外的数据用的,它本身就是一个键值对(Bundle),可以自定义名称和值(value或resource)。
使用meta-data的好处是,它只需要在manifest.xml一个文件中配置,就可以在代码中的各个组件里去动态获取,实现相应的需求。集中配置的方式方便了后续的管理与修改,配合上 gradle 的 manifestPlaceholders 还可以做更加集中化的处理。
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.metadatademo" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="23" android:targetSdkVersion="25" /> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="application" > <activity android:name="MainActivity" android:label="activity" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <meta-data android:name="meta_data" android:value="activity_meta_data_value" /> </activity> <activity-alias android:name="MyActivityAlias" android:label="activity_alias" android:targetActivity=".MainActivity" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.DEFAULT" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <meta-data android:name="meta_data" android:value="activity_alias_meta_data_value" /> </activity-alias> <meta-data android:name="meta_data" android:value="application_meta_data_value" /> <provider android:name="MyContentProvider" android:authorities="com.chy.authorities" android:label="provider" > <meta-data android:name="meta_data" android:value="provider_meta_data_value" /> </provider> <receiver android:name="MyBroadcastReceiver" android:label="receiver" > <intent-filter> <action android:name="android.intent.action.PHONE_STATE" /> </intent-filter> <meta-data android:name="meta_data" android:value="receiver_meta_data_value" /> </receiver> <service android:name="MyService" android:label="service" > <meta-data android:name="meta_data" android:value="service_meta_data_value" /> </service> </application> </manifest>
public class MainActivity extends Activity { private TextView textview; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); textview = (TextView) findViewById(R.id.textview); PackageManager pm = getPackageManager(); //application meta-data try { ApplicationInfo applicationInfo = pm.getApplicationInfo(getPackageName(), PackageManager.GET_META_DATA); addText(applicationInfo.metaData.getString("meta_data")); } catch (NameNotFoundException e) { e.printStackTrace(); } //"activity"或"activity-alias" meta-data try { ActivityInfo activityInfo = pm.getActivityInfo(getComponentName(), PackageManager.GET_META_DATA); addText(activityInfo.metaData.getString("meta_data")); } catch (NameNotFoundException e) { e.printStackTrace(); } //"provider" meta-data ComponentName providerComponentInfo = new ComponentName(this, MyContentProvider.class); try { ProviderInfo providerInfo = pm.getProviderInfo(providerComponentInfo, PackageManager.GET_META_DATA); addText(providerInfo.metaData.getString("meta_data")); } catch (NameNotFoundException e) { e.printStackTrace(); } //"receiver" meta-data ComponentName receiverComponentInfo = new ComponentName(this, MyBroadcastReceiver.class); try { ActivityInfo receiverInfo = pm.getReceiverInfo(receiverComponentInfo, PackageManager.GET_META_DATA); addText(receiverInfo.metaData.getString("meta_data")); } catch (NameNotFoundException e) { e.printStackTrace(); } //"service" meta-data ComponentName serviceComponentInfo = new ComponentName(this, MyService.class); try { ServiceInfo serviceInfo = pm.getServiceInfo(serviceComponentInfo, PackageManager.GET_META_DATA); addText(serviceInfo.metaData.getString("meta_data")); } catch (NameNotFoundException e) { e.printStackTrace(); } } private void addText(String str) { textview.setText(textview.getText().toString() + "\n" + str); } }
public class MyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context arg0, Intent arg1) {
}
}
public class MyContentProvider extends ContentProvider { @Override public int delete(Uri arg0, String arg1, String[] arg2) { return 0; } @Override public String getType(Uri arg0) { return null; } @Override public Uri insert(Uri arg0, ContentValues arg1) { return null; } @Override public boolean onCreate() { return false; } @Override public Cursor query(Uri arg0, String[] arg1, String arg2, String[] arg3, String arg4) { return null; } @Override public int update(Uri arg0, ContentValues arg1, String arg2, String[] arg3) { return 0; } }
public class MyService extends Service {
@Override
public IBinder onBind(Intent arg0) {
return null;
}
}
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.metadatademo.MainActivity" >
<TextView
android:id="@+id/textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
在 Manifest.xml 配置 meta-data
<application android:name=".test.global.MyApplication" ……> <meta-data android:name="mipmap" android:resource="@mipmap/ic_launcher" /> <meta-data android:name="color" android:resource="@color/colorPrimary" /> <meta-data android:name="layout" android:resource="@layout/activity_test" /> <meta-data android:name="string" android:resource="@string/app_name" /> <meta-data android:name="number" android:value="123" /> <meta-data android:name="text" android:value="abc" /> …… </application>
然后在 MyApplication.java 中将它们打印出来
public class MyApplication extends Applicatoin {
@Override
public void onCreate() {
super.onCreate();
String[] keys = {"mipmap", "color", "layout", "string", "number", "text"};
for(String key : keys) {
print(MetaUtil.fromApplication(this, key));
}
}
private void print(Object obj) {
System.out.println(obj + " : " + obj.getClass());
}
}
搜索关键词使用 System.out 来进行筛选,可以得出如下结论
在 meta-data 中,有个很容易让人忽略的小细节。
因此,在引入第三方SDK时,如果有全数字,且超过13位的APPID这种,很容易获取出错(最后得到的是其它数值)
我做了一个工具类,用来解决这种情况(需要被当成字符串的全数字前加一个@作为标记符)
public class MetaUtil { /** * 由于是自动识别类型,全数字会被识别为Integer或Float,且float和double还会自动被转为科学计数法以保留其最大精度 */ private static String toString(Object value) { String result = null; if (value != null) { String valueClassName = value.getClass().getSimpleName(); switch (valueClassName) { case "Long": case "Float": case "Double": NumberFormat numberFormat = NumberFormat.getInstance(); //不使用分组方式显示数据(即科学计数法),但这样可能会导致精度丢失,精度最多13位 numberFormat.setGroupingUsed(false); result = numberFormat.format(value); break; case "String": //当数字多于13位时(或者保守起见,只要是需要被当成字符串的全数字)都在其首位加上一个@符号 result = value.toString(); if (result.startsWith("@")) { result = result.substring(1); } break; default: result = String.valueOf(value); break; } } return result; } public static Object fromApplication(Context context, String key) { PackageManager packageManager = context.getPackageManager(); try { ApplicationInfo applicationInfo = packageManager.getApplicationInfo(context.getPackageName(), PackageManager.GET_META_DATA); return applicationInfo.metaData.get(key); } catch (PackageManager.NameNotFoundException e) { e.printStackTrace(); } return null; } public static String fromApplicationToStr(Context context, String key) { return toString(fromApplication(context, key)); } public static Object fromActivity(FragmentActivity activity, String key) { PackageManager packageManager = activity.getPackageManager(); try { ActivityInfo activityInfo = packageManager.getActivityInfo(activity.getComponentName(), PackageManager.GET_META_DATA); return activityInfo.metaData.get(key); } catch (PackageManager.NameNotFoundException e) { e.printStackTrace(); } return null; } public static String fromActivityToStr(FragmentActivity activity, String key) { return toString(fromActivity(activity, key)); } public static Object fromService(Service service, String key) { PackageManager packageManager = service.getPackageManager(); ComponentName componentName = new ComponentName(service, service.getClass()); try { ServiceInfo serviceInfo = packageManager.getServiceInfo(componentName, PackageManager.GET_META_DATA); return serviceInfo.metaData.get(key); } catch (PackageManager.NameNotFoundException e) { e.printStackTrace(); } return null; } public static String fromServiceToStr(Service service, String key) { return toString(fromService(service, key)); } /** * BroadcastReceiver 的 context * 静态注册:android.app.ReceiverRestrictedContext * 动态注册:在哪个 activity 注册的,就是那个 activity 的 context */ public static Object fromReceiver(Context context, BroadcastReceiver receiver, String key) { PackageManager packageManager = context.getPackageManager(); ComponentName componentName = new ComponentName(context, receiver.getClass()); try { ActivityInfo serviceInfo = packageManager.getReceiverInfo(componentName, PackageManager.GET_META_DATA); return serviceInfo.metaData.get(key); } catch (PackageManager.NameNotFoundException e) { e.printStackTrace(); } return null; } public static String fromReceiverToStr(Context context, BroadcastReceiver receiver, String key) { return toString(fromReceiver(context, receiver, key)); } }
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