Android之SystemUI加载流程和NavigationBar的分析

Android之SystemUI加载流程和NavigationBar的分析

本篇只分析SystemUI的加载过程和SystemUI的其中的一个模块StatusBar的小模块NavigationBar，以Android6.0代码进行分析

AndroidManifest.xml

SystemUIService

跟StatusBar相关的服务为SystemUIService,我们查看SystemUIService源码

public class SystemUIService extends Service {

    @Override
    public void onCreate() {
        super.onCreate();
        ((SystemUIApplication) getApplication()).startServicesIfNeeded();
        //获取Application调用startServicesIfNeeded
    }

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

    /*打印堆栈信息*/
    @Override
    protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
        SystemUI[] services = ((SystemUIApplication) getApplication()).getServices();
        if (args == null || args.length == 0) {
            for (SystemUI ui: services) {
                pw.println("dumping service: " + ui.getClass().getName());
                ui.dump(fd, pw, args);
            }
        } else {
            String svc = args[0];
            for (SystemUI ui: services) {
                String name = ui.getClass().getName();
                if (name.endsWith(svc)) {
                    ui.dump(fd, pw, args);
                }
            }
        }
    }
}

分析SystemUIService代码，可以知道SystemUI主要做了两件事

那么SystemUIService又是哪里开始启动的呢？竟然SystemUIService是个服务，那么启动服务要么就是startService
要么就是bindService进行启动，其启动方式则需要通过Intent来传入类名或者包名，因此在源码中搜索SystemUIService可以对比发现，它在
frameworks\base\services\java\com\android\server\SystemServer.java中进行启动

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);
}

在SystemServer的run方法中startOtherServices来启动SystemUIService服务，至于SystemServer则涉及到Android的启动流程，其大概流程为

int -> ServerManager -> Zygote -> SystemServer

SystemServer中会初始化一些Android的java层的服务，如ActivityManagerService、WindowManagerService等

这里SystemUI的加载过程就到此告一段落了，下面分析StatusBar的加载流程

上面讲到在SystemUIService的onCreate中获取SystemUIApplication对象来初始化SystemUI相关的类，这些类里面就包括了StatusBar相关的类，我们查看SystemUIApplication类

SystemUIApplication

onCreate

@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);
    //注释广播
    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) {
            //开启直接返回
            if (mBootCompleted) return;

            if (DEBUG) Log.v(TAG, "BOOT_COMPLETED received");
            unregisterReceiver(this);
            //标记启动
            mBootCompleted = true;
            //服务是否启动
            if (mServicesStarted) {
                final int N = mServices.length;
                for (int i = 0; i < N; i++) {
                    //回调各服务的onBootCompleted函数
                    mServices[i].onBootCompleted();
                }
            }
        }
    }, filter);
}

在SystemUIApplication的onCreate中主要做了

startServicesIfNeeded

SystemUIService中的onCreate启动了这个方法，我们着重分析这个方法

public void startServicesIfNeeded() {
    if (mServicesStarted) {
        return;
    }

    if (!mBootCompleted) {
        // check to see if maybe it was already completed long before we began
        // see ActivityManagerService.finishBooting()
        //获取系统文件中的sys.boot_completed的值
        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 cl = SERVICES[i];
        if (DEBUG) Log.d(TAG, "loading: " + cl);
        //实例化各个类实例，放入mServices数组中
        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();
        }
    }
    //服务启动标志
    mServicesStarted = true;
}

这个方法中，首先判断mServicesStarted标志为来判断SystemUI相关的服务是否启动，同时根据系统配置文件来检查ActivityManagerService是否finishBooting，然后通过类加载机制来初始化SERVICES数组里面相关的类加入mServices中，然后start

 /**
 * The classes of the stuff to start.
 */
private final Class[] SERVICES = new Class[] {
        com.android.systemui.tuner.TunerService.class,//定制状态栏服务
        com.android.systemui.keyguard.KeyguardViewMediator.class,//锁屏相关
        com.android.systemui.recents.Recents.class,//近期任务
        com.android.systemui.volume.VolumeUI.class,//音量条
        com.android.systemui.statusbar.SystemBars.class,//状态栏
        com.android.systemui.usb.StorageNotification.class,//通知栏
        com.android.systemui.power.PowerUI.class,//电源相关
        com.android.systemui.media.RingtonePlayer.class,//铃声播放相关
};

/**
 * Hold a reference on the stuff we start.
 */
private final SystemUI[] mServices = new SystemUI[SERVICES.length];

从mServices和SERVICES的定义可以发现SERVICES是一组包含全路径的相关的类,这些类包含一些我们常见的TunerService（定制状态栏服务）、
KeyguardViewMediator（锁屏相关）、Recents(近期任务)、VolumeUI(音量条)、SystemBars(状态栏)、StorageNotification（通知栏）、