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)。 它可以包含在以下6个组件中:- <application>
- <activity>
- <activity-alias>
- <provider>
- <receiver>
- <service>
meta-data 主要有以下几个常见用途:- 在APP发布的时候,通过修改 meta-data,来标记不同的“发布渠道”,以方便脚本自动化修改、打包、发布。
- 与 activity-alias 配合使用,meta-data作为标记,来实现类似“拨号-联系人-短信”应用的通过同一个activity打开不同的选项卡。
- 作为日志标记,在公共父类中获取该值并作为是否打印日志的标记,用多态化的思想控制日志,免去了冗杂的在代码中进行分别配置。
实验代码Manifest.xml<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas./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>
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MainActivity.javapackage com.example.metadatademo;
import android.app.Activity;
import android.content.ComponentName;
import android.content.pm.ActivityInfo;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.ProviderInfo;
import android.content.pm.ServiceInfo;
import android.os.Bundle;
import android.widget.TextView;
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);
}
}
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MyBroadcastReceiver.javapackage com.example.metadatademo;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
public class MyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context arg0, Intent arg1) {
}
}
MyContentProvider.javapackage com.example.metadatademo;
import android.content.ContentProvider;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
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;
}
}
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MyService.javapackage com.example.metadatademo;
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
public class MyService extends Service {
@Override
public IBinder onBind(Intent arg0) {
return null;
}
}
activity_main.xml<RelativeLayout xmlns:android="http://schemas./apk/res/android"
xmlns:tools="http://schemas./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>
运行截图可以发现由于在AndroidManifest.xml中的<activity>标签的子标签<intent-filter>中存在以下两句,因此会生成2个应用图标,它们的名字是“android:label”的值。 <action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
注意观察:虽然点击两个图标打开的都是同一个activity但是由于getComponentName()的返回值不同(分别代表了activity和activity-alias),因此,它们获取到的meta-data值也不同。
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