Dagger2在SystemUI中的应用，kotlin开发android教程

src/com/android/systemui/SystemUIAppComponentFactory.java

public Application instantiateApplicationCompat(
@N
onNull ClassLoader cl, @NonNull String className)
throws InstantiationException, IllegalAccessException, ClassNotFoundException {
Application app = super.instantiateApplicationCompat(cl, className);
if (app instanceof ContextInitializer) {
((ContextInitializer) app).setContextAvailableCallback(
context -> {
SystemUIFactory.createFromConfig(context);
SystemUIFactory.getInstance().getSysUIComponent().inject(
SystemUIAppComponentFactory.this);
}
);
}

return app;
}

在SystemUIApplication onCreate时回调 ContextAvailableCallback, 构建SystemUIFactory，并对它进行初始化

src/com/android/systemui/SystemUIFactory.java

public static void createFromConfig(Context context, boolean fromTest) {
if (mFactory != null) {
return;
}

final String clsName = context.getString(R.string.config_systemUIFactoryComponent);
if (clsName == null || clsName.length() == 0) {
throw new RuntimeException(“No SystemUIFactory component configured”);
}

try {
Class cls = null;
cls = context.getClassLoader().loadClass(clsName);
// 创建SystemUIFactory实例
mFactory = (SystemUIFactory) cls.newInstance();
// 初始化SystemUIFactory
mFactory.init(context, fromTest);
} catch (Throwable t) {
Log.w(TAG, "Error creating SystemUIFactory component: " + clsName, t);
throw new RuntimeException(t);
}
}

public void init(Context context, boolean fromTest)
throws ExecutionException, InterruptedException {
…
// 获取dagger组件
mRootComponent = buildGlobalRootComponent(context);
…

// 获取systemui的dagger组件
// And finally, retrieve whatever SysUI needs from WMShell and build SysUI.
SysUIComponent.Builder builder = mRootComponent.getSysUIComponent();
mSysUIComponent = builder.build();
…

// 构建Dependency实例并初始化
// Every other part of our codebase currently relies on Dependency, so we
// really need to ensure the Dependency gets initialized early on.
Dependency dependency = mSysUIComponent.createDependency();
dependency.start();
}

protected GlobalRootComponent buildGlobalRootComponent(Context context) {
return DaggerGlobalRootComponent.builder()
.context(context)
.build();
}

Dependency组件使用@Lazy标签懒加载： 首先构建LazyDependencyCreator放入mProviders，然后在真正使用dependency时调用createDependency进行创建

src/com/android/systemui/Dependency.java

private final ArrayMap mDependencies = new ArrayMap<>();
private final ArrayMap mProviders = new ArrayMap<>();

@Inject Lazy mActivityStarter;
@Inject Lazy mBroadcastDispatcher;
@Inject Lazy mAsyncSensorManager;
@Inject Lazy mBluetoothController;

protected void start() {
// 构建LazyDependencyCreator放入mProviders
mProviders.put(TIME_TICK_HANDLER, mTimeTickHandler::get);
mProviders.put(BG_LOOPER, mBgLooper::get);
mProviders.put(MAIN_LOOPER, mMainLooper::get);
mProviders.put(MAIN_HANDLER, mMainHandler::get);
mProviders.put(MAIN_EXECUTOR, mMainExecutor::get);
mProviders.put(BACKGROUND_EXECUTOR, mBackgroundExecutor::get);
mProviders.put(ActivityStarter.class, mActivityStarter::get);
mProviders.put(BroadcastDispatcher.class, mBroadcastDispatcher::get);
…

// 获取dependency
private synchronized T getDependencyInner(Object key) {
@SuppressWarnings(“unchecked”)
T obj = (T) mDependencies.get(key);
if (obj == null) {
// 若未创建则创建
obj = createDependency(key);
mDependencies.put(key, obj);
…
}
return obj;
}

public T createDependency(Object cls) {
Preconditions.checkArgument(cls instanceof DependencyKey || cls instanceof Class);

@SuppressWarnings(“unchecked”)
LazyDependencyCreator provider = mProviders.get(cls);
if (provider == null) {
throw new IllegalArgumentException("Unsupported dependency " + cls

“. " + mProviders.size() + " providers known.”);
}

// 这里调用的就是lazy.get()
return provider.createDependency();
}

private interface LazyDependencyCreator {
T createDependency();
}

Application创建好之后SystemUI的主Service将启动起来，并逐个启动其他Service。

src/com/android/systemui/SystemUIService.java

public void onCreate() {
super.onCreate();
// Start all of SystemUI
((SystemUIApplication) getApplication()).startServicesIfNeeded();
…
}

ContextComponentHelper声明在dagger组件中获取，实现类是ContextComponentResolver

src/com/android/systemui/SystemUIApplication.java

private void startServicesIfNeeded(String metricsPrefix, String[] services) {
…
final int N = services.length;
for (int i = 0; i < N; i++) {
String clsName = services[i];
if (DEBUG) Log.d(TAG, "loading: " + clsName);
log.traceBegin(metricsPrefix + clsName);
long ti = System.currentTimeMillis();
try {
// 从ContextComponentHelper中获取对应组件的实例
SystemUI obj = mComponentHelper.resolveSystemUI(clsName);
if (obj == null) {
Constructor constructor = Class.forName(clsName).getConstructor(Context.class);
obj = (SystemUI) constructor.newInstance(this);
}
mServices[i] = obj;
} catch (ClassNotFoundException
| NoSuchMethodException
| IllegalAccessException
| InstantiationException
| InvocationTargetException ex) {
throw new RuntimeException(ex);
}

if (DEBUG) Log.d(TAG, "running: " + mServices[i]);
// 调用SystemUI组件的start()方法
mServices[i].start();

ContextComponentHelper声明在dagger组件中获取，实现类是ContextComponentResolver

src/com/android/systemui/dagger/SysUIComponent.java

@SysUISingleton
ContextComponentHelper getContextComponentHelper();

@Override
public SystemUI resolveSystemUI(String className) {
return resolve(className, mSystemUICreators);
}

private T resolve(String className, Map, Provider> creators) {
try {
Class clazz = Class.forName(className);
Provider provider = creators.get(clazz);
return provider == null ? null : provider.get();
} catch (ClassNotFoundException e) {
return null;
}
}

try {
Class clazz = Class.forName(className);
Provider provider = creators.get(clazz);
return provider == null ? null : provider.get();
} catch (ClassNotFoundException e) {
return null;
}
}