SystemUI分析

　　SystemUI是安卓的一个系统APP，负责的内容有系统通知栏，状态栏，最近应用程序，锁屏，壁纸，屏保，系统对话框，截屏，录屏等功能。

       Apk的路径位于/system/priv-app，源码code位于frameworks/base/packages/SystemUI。

       1.Android.mk

       2.AndroidManifest.xml配置文件表明了APP要求的权限，特征以及四大组件。

       3.初始化流程

1.SystemUI启动

SystemUI是核心系统应用，需要开机启动，启动SystemUI进程，是通过启动SystemUIService来实现的。

 

 

frameworks\base\services\java\com\android\server\SystemServer.java

 

SystemServer启动后，会在SystemServer Main Thread启动ActivityManagerService，当ActivityManagerService  systemReady后，会去启动SystemUIService。

 

 mActivityManagerService.systemReady(new Runnable() {
            @Override
            public void run() {

           ...

           try {
                    startSystemUi(context);
                } catch (Throwable e) {
                    reportWtf("starting System UI", e);
                }

由如上可以看出，startSystemUi不是在SystemServer Main thread，而是在ActivityManagerService Thread。

 

 static final void startSystemUi(Context context) {
        Intent intent = new Intent();
        intent.setComponent(new ComponentName("com.android.systemui",
                    "com.android.systemui.SystemUIService"));
        //Slog.d(TAG, "Starting service: " + intent);
        context.startServiceAsUser(intent, UserHandle.OWNER);
    }

通过startServiceAsUser，SystemUIService就启动了，即SystemUI进程开机启动。

 

 

2.SystemUI Services启动

SystemServer启动SystemUIService后，会走到SystemUIService的onCreate函数。

public class SystemUIService extends Service {


    @Override
    public void onCreate() {
        super.onCreate();
        ((SystemUIApplication) getApplication()).startServicesIfNeeded();
    }

SystemUIService就是一个普通的Service，在onCreate里面，会调用SystemUIApplication的services

 

/**
 * Application class for SystemUI.
 */
public class SystemUIApplication extends Application {


    private static final String TAG = "SystemUIService";
    private static final boolean DEBUG = false;


    /**
     * The classes of the stuff to start.
     */
    private final Class<?>[] SERVICES = new Class[] {
            com.android.systemui.tuner.TunerService.class,
            com.android.systemui.keyguard.KeyguardViewMediator.class,
            com.android.systemui.recents.Recents.class,
            com.android.systemui.volume.VolumeUI.class,
            com.android.systemui.statusbar.SystemBars.class,
            com.android.systemui.usb.StorageNotification.class,
            com.android.systemui.power.PowerUI.class,
            com.android.systemui.media.RingtonePlayer.class,
    };

 

SystemUIApplication是一个Application实现，重写Application相关函数。

SystemUIApplication定义了很多System Panel，这里叫做SERVICES，但是并非是真正的service.

 

SystemUI应用定义了一个抽象的SystemUI类，根据Java抽象化的特征，可以使开发更加灵活。

 

SystemUI相关的类图关系如下：

从SystemUI继承了很多的Panel，这些Panel有我们很熟悉的，比如Recents(近期任务栏)，VolumeUI(音量条)，SystemBars(状态栏)等。

 

 

回到SystemUIApplication里的startService函数：

/**
 * Makes sure that all the SystemUI services are running. If they are already running, this is a
 * no-op. This is needed to conditinally start all the services, as we only need to have it in
 * the main process.
 *
 * <p>This method must only be called from the main thread.</p>
 */
public void startServicesIfNeeded() {
    if (mServicesStarted) {
        return;
    }

    if (!mBootCompleted) {
        // check to see if maybe it was already completed long before we began
        // see ActivityManagerService.finishBooting()
        if ("1".equals(SystemProperties.get("sys.boot_completed"))) {
            mBootCompleted = true;
            if (DEBUG) Log.v(TAG, "BOOT_COMPLETED was already sent");
        }
    }

    Log.v(TAG, "Starting SystemUI services.");
    final int N = SERVICES.length;
    for (int i=0; i<N; i++) {
        Class<?> cl = SERVICES[i];
        if (DEBUG) Log.d(TAG, "loading: " + cl);
        try {
            mServices[i] = (SystemUI)cl.newInstance();
        } catch (IllegalAccessException ex) {
            throw new RuntimeException(ex);
        } catch (InstantiationException ex) {
            throw new RuntimeException(ex);
        }
        mServices[i].mContext = this;
        mServices[i].mComponents = mComponents;
        if (DEBUG) Log.d(TAG, "running: " + mServices[i]);
        mServices[i].start();

        if (mBootCompleted) {
            mServices[i].onBootCompleted();
        }
    }
    mServicesStarted = true;
}

这个函数主要是实例化以及启动SystemUI Services(这里的Service并非是真正的service)，这样通过SystemUIService的启动，SystemUI核心的services也启动了。

 

 

在SystemUIApplication类的onCreate里面，会注册开机完成广播，并将开机完成事件，给到SystemUI Services.

@Override
  public void onCreate() {
      super.onCreate();
      // Set the application theme that is inherited by all services. Note that setting the
      // application theme in the manifest does only work for activities. Keep this in sync with
      // the theme set there.
      setTheme(R.style.systemui_theme);

      IntentFilter filter = new IntentFilter(Intent.ACTION_BOOT_COMPLETED);
      filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY);
      registerReceiver(new BroadcastReceiver() {
          @Override
          public void onReceive(Context context, Intent intent) {
              if (mBootCompleted) return;

              if (DEBUG) Log.v(TAG, "BOOT_COMPLETED received");
              unregisterReceiver(this);
              mBootCompleted = true;
              if (mServicesStarted) {
                  final int N = mServices.length;
                  for (int i = 0; i < N; i++) {
                      mServices[i].onBootCompleted();
                  }
              }
          }
      }, filter);
  }

SystemUI Services启动后，根据各Services的功能，SystemUI开始各司其职的正常工作起来。