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Android安卓进程保活(三)双进程拉活(Java层)

Android进程保活·双进程拉活(Java层)

Android进程


此文章代码Github有提交https://github.com/NorthernBrain/DoubleService


首先你要知道Android中的进程以及它的优先级,下面来说明它进程
  1. 前台进程 (Foreground process)
  2. 可见进程 (Visible process)
  3. 服务进程 (Service process)
  4. 后台进程 (Background process)
  5. 空进程 (Empty process)

下面进行解释:


前台进程(Foreground process):
用户当前操作所必需的进程。如果一个进程满足以下任一条件,即视为前台进程:
  • 托管用户正在交互的 Activity(已调用 Activity 的 onResume() 方法)
  • 托管某个 Service,后者绑定到用户正在交互的 Activity
  • 托管正在“前台”运行的 Service(服务已调用 startForeground())
  • 托管正执行一个生命周期回调的 Service(onCreate()、onStart() 或 onDestroy())
  • 托管正执行其 onReceive() 方法的 BroadcastReceiver
        通常,在任意给定时间前台进程都为数不多。只有在内存不足以支持它们同时继续运行这一万不得已的情况下,系统才会终止它们。 此时,设备往往已达到内存分页状态,因此需要终止一些前台进程来确保用户界面正常响应。


可见进程 (Visible process):
没有任何前台组件、但仍会影响用户在屏幕上所见内容的进程。 如果一个进程满足以下任一条件,即视为可见进程:
  • 托管不在前台、但仍对用户可见的 Activity(已调用其 onPause() 方法)。例如,如果前台 Activity 启动了一个对话框,允许在其后显示上一 Activity,则有可能会发生这种情况。
  • 托管绑定到可见(或前台)Activity 的 Service。

可见进程被视为是极其重要的进程,除非为了维持所有前台进程同时运行而必须终止,否则系统不会终止这些进程。


服务进程 (Service process):
正在运行已使用 startService() 方法启动的服务且不属于上述两个更高类别进程的进程。尽管服务进程与用户所见内容没有直接关联,但是它们通常在执行一些用户关心的操作(例如,在后台播放音乐或从网络下载数据)。因此,除非内存不足以维持所有前台进程和可见进程同时运行,否则系统会让服务进程保持运行状态。


后台进程 (Service process):
包含目前对用户不可见的 Activity 的进程(已调用 Activity 的 onStop() 方法)。这些进程对用户体验没有直接影响,系统可能随时终止它们,以回收内存供前台进程、可见进程或服务进程使用。 通常会有很多后台进程在运行,因此它们会保存在 LRU (最近最少使用)列表中,以确保包含用户最近查看的 Activity 的进程最后一个被终止。如果某个 Activity 正确实现了生命周期方法,并保存了其当前状态,则终止其进程不会对用户体验产生明显影响,因为当用户导航回该 Activity 时,Activity 会恢复其所有可见状态。


空进程 (Empty process):
不含任何活动应用组件的进程。保留这种进程的的唯一目的是用作缓存,以缩短下次在其中运行组件所需的启动时间。 为使总体系统资源在进程缓存和底层内核缓存之间保持平衡,系统往往会终止这些进程。


进程优先级:
首先空进程是最先被回收的,其次便是后台进程,依次往上,前台进程是最后才会被结束。


Android进程保活

有很多种方法可以实现Android的进程保活,比如通过 1像素且透明Activity提升App进程优先级通过设置前台Service提升App进程优先级Java层的双进程拉活JobScheduler实现NDK双进程守护使用账户同步拉活workmanager实现

下面这幅图,说明的是:
  • 红色部分是容易被回收的进程,属于android进程
  • 绿色部分是较难被回收的进程,属于android进程
  • 其他部分则不是android进程,也不会被系统回收,一般是ROM自带的app和服务才能拥有

本篇文章介绍的是进程第三种方式:

  • 双进程拉活(Java层)
双进程拉活(Java层):

当一个进程结束后,立刻调用启动另一个进程,这样实现互相调用,互相启动(只有在一个进程结束时候才会启动另一个进程)


首先创建LocalService.java继承自Service(android.app.Service):↓

public class LocalService extends Service {
    @Override
    public IBinder onBind(Intent intent) {
        return new LocalBinder();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        /*第一个参数Intent
        第二个参数ServiceConnection*/

        /**
         *  第三个参数介绍:
        * Flag for {@link #bindService}: automatically create the service as long
        * as the binding exists.  Note that while this will create the service,
        * its {@link android.app.Service#onStartCommand}
        * method will still only be called due to an
        * explicit call to {@link #startService}.  Even without that, though,
        * this still provides you with access to the service object while the
        * service is created.
        *
        * <p>Note that prior to {@link android.os.Build.VERSION_CODES#ICE_CREAM_SANDWICH},
        * not supplying this flag would also impact how important the system
        * consider's the target service's process to be.  When set, the only way
        * for it to be raised was by binding from a service in which case it will
        * only be important when that activity is in the foreground.  Now to
        * achieve this behavior you must explicitly supply the new flag
        * {@link #BIND_ADJUST_WITH_ACTIVITY}.  For compatibility, old applications
        * that don't specify {@link #BIND_AUTO_CREATE} will automatically have
        * the flags {@link #BIND_WAIVE_PRIORITY} and
        * {@link #BIND_ADJUST_WITH_ACTIVITY} set for them in order to achieve
        * the same result.
        */
        bindService(new Intent(this,RemoteService.class),connection,Context.BIND_AUTO_CREATE);
        return super.onStartCommand(intent, flags, startId);
    }

    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            //绑定成功
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            //当RemoteService所处进程被干掉就重新启动
            startService(new Intent(LocalService.this,RemoteService.class));
            bindService(new Intent(LocalService.this,RemoteService.class),connection,Context.BIND_IMPORTANT);
        }
    };

    private class LocalBinder extends Binder {

    }
}

对LocalService在清单文件中进行注册
<service android:name=".LocalService" />

创建RemoteService.java继承自Service(android.app.Service):↓
public class RemoteService extends Service {
    public RemoteService() {
    
    }

    @Override
    public IBinder onBind(Intent intent) {
        return new RemoteBinder();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        /*第一个参数Intent
        第二个参数ServiceConnection
        第三个参数介绍:

        /**
        * Flag for {@link #bindService}: automatically create the service as long
        * as the binding exists.  Note that while this will create the service,
        * its {@link android.app.Service#onStartCommand}
        * method will still only be called due to an
        * explicit call to {@link #startService}.  Even without that, though,
        * this still provides you with access to the service object while the
        * service is created.
        *
        * <p>Note that prior to {@link android.os.Build.VERSION_CODES#ICE_CREAM_SANDWICH},
        * not supplying this flag would also impact how important the system
        * consider's the target service's process to be.  When set, the only way
        * for it to be raised was by binding from a service in which case it will
        * only be important when that activity is in the foreground.  Now to
        * achieve this behavior you must explicitly supply the new flag
        * {@link #BIND_ADJUST_WITH_ACTIVITY}.  For compatibility, old applications
        * that don't specify {@link #BIND_AUTO_CREATE} will automatically have
        * the flags {@link #BIND_WAIVE_PRIORITY} and
        * {@link #BIND_ADJUST_WITH_ACTIVITY} set for them in order to achieve
        * the same result.
        */
        bindService(new Intent(this,RemoteService.class),connection,Context.BIND_AUTO_CREATE);
        return super.onStartCommand(intent, flags, startId);
    }

    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            //绑定成功
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            //当RemoteService所处进程被干掉就重新启动
            startService(new Intent(RemoteService.this,LocalService.class));
            bindService(new Intent(RemoteService.this,LocalService.class),connection,Context.BIND_IMPORTANT);
        }
    };

    private class RemoteBinder extends Binder{
    
    }
}


对RemoteService 在清单文件中进行注册,再制定一个进程名字,好区分
<service
            android:name=".RemoteService"
            android:enabled="true"
            android:exported="true"
            android:process=":remote" />
        <!--
            android:process=":remote"
            指定进程名
        -->


最后在MainActivity启动其中一个服务LocalService:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //双进程拉活(Java层)
        startService(new Intent(this,LocalService.class));
    }
}

这样就完成了双进程拉活

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