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。
- 引入第三方SDK时,配置appId和appKey
- 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。
- 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。
基础入门 —— 从组件中获取meta-data
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。
Manifest.xml
<?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>
MainActivity.java
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);
}
}
MyBroadcastReceiver.java
public class MyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context arg0, Intent arg1) {
}
}
MyContentProvider.java
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;
}
}
MyService.java
public class MyService extends Service {
@Override
public IBinder onBind(Intent arg0) {
return null;
}
}
activity_main.xml
<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>
进阶 —— 获取各种类型的值
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
- resource中存储的都是对象的ID,整型
- value支持 Integer、Float、Boolean、String 这四种常用类型
终极 —— 获取字符串
在 meta-data 中,有个很容易让人忽略的小细节。
- meta-data 的 value 如果是全数字,则获取为数字(较长的数字,为了保持精度,获取时会被自动使用科学计数法表示)
- 只要全数字的value中出现了一个非数字,则会被当成字符串处理
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));
}
}