本文代码基于Android 9.0分析,个人理解能力有限,如有不对请多指教。
SystemUI是在开机过程中SystemServer启动的,SystemServer的startOtherServices()中
/*frameworks/base/services/java/com/android/server/SystemServer.java*/
private void startOtherServices() {
...
try {
startSystemUi(context, windowManagerF);
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
...
}
//startSystemUi方法
static final void startSystemUi(Context context, WindowManagerService windowManager) {
Intent intent = new Intent();
intent.setComponent(new ComponentName("com.android.systemui",
"com.android.systemui.SystemUIService"));
intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
context.startServiceAsUser(intent, UserHandle.SYSTEM);
windowManager.onSystemUiStarted();
}
可以看到该方法会启动systemUi的SystemUIService服务。windowManager.onSystemUiStarted()方法最终会通过绑定的方式启动SystemUi的KeyguardService服务。
SystemUIService继承Service,是一个标准的android服务,所以必须重载onCreate接口:
//frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIService.java
@Override
public void onCreate() {
super.onCreate();
((SystemUIApplication) getApplication()).startServicesIfNeeded();
... //省略不重要代码
}
SystemUIService的onCreate方法中又调用了SystemUIApplication的startServicesIfNeeded方法。
//frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIApplication.java
public void startServicesIfNeeded() {
String[] names = getResources().getStringArray(R.array.config_systemUIServiceComponents);
startServicesIfNeeded(names);
}
先看下names里面存储的是什么。
config_systemUIServiceComponents:
<!-- frameworks/base/packages/SystemUI/res/values/config.xml --!>
<string-array name="config_systemUIServiceComponents" translatable="false">
<item>com.android.systemui.Dependency</item>
<item>com.android.systemui.util.NotificationChannels</item>
<item>com.android.systemui.statusbar.CommandQueue$CommandQueueStart</item>
<item>com.android.systemui.keyguard.KeyguardViewMediator</item>
<item>com.android.systemui.recents.Recents</item>
<item>com.android.systemui.volume.VolumeUI</item>
<item>com.android.systemui.stackdivider.Divider</item>
<item>com.android.systemui.SystemBars</item>
<item>com.android.systemui.usb.StorageNotification</item>
<item>com.android.systemui.power.PowerUI</item>
<item>com.android.systemui.media.RingtonePlayer</item>
<item>com.android.systemui.keyboard.KeyboardUI</item>
<item>com.android.systemui.pip.PipUI</item>
<item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item>
<item>@string/config_systemUIVendorServiceComponent</item>
<item>com.android.systemui.util.leak.GarbageMonitor$Service</item>
<item>com.android.systemui.LatencyTester</item>
<item>com.android.systemui.globalactions.GlobalActionsComponent</item>
<item>com.android.systemui.ScreenDecorations</item>
<item>com.android.systemui.fingerprint.FingerprintDialogImpl</item>
<item>com.android.systemui.SliceBroadcastRelayHandler</item>
</string-array>
config_systemUIServiceComponents是一系列包名加类名。这些类都继承自SystemUI类,SystemUI是一个抽象类,其中有一个抽象方法
public abstract void start();
读取到String数组names里面,然后调用带参数的startServicesIfNeeded方法:
private void startServicesIfNeeded(String[] services) {
...
//创建SystemUI数组,长度为names的长度
mServices = new SystemUI[services.length];
...
//开始遍历services数组,也就是之前的names数组
final int N = services.length;
for (int i = 0; i < N; i++) {
String clsName = services[i];
...
long ti = System.currentTimeMillis();
Class cls;
try {
cls = Class.forName(clsName);
//实例化取出的class
mServices[i] = (SystemUI) cls.newInstance();
} catch(ClassNotFoundException ex){
throw new RuntimeException(ex);
} 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]);
//调用start方法启动
mServices[i].start();
...
if (mBootCompleted) {
mServices[i].onBootCompleted();
}
...
}
每一个系统ui元素(包括statusBar,PowerUI等)都必须继承SystemUI这个抽象类,并重载其中的start方法,这是一种比较灵活的编程方式,它允许我们在后期对系统UI元素进行轻松的扩展或者删除。具体每个UI元素的启动将在后续章节分析。