Activity是如何启动的？ - MrWu94/AndroidNote GitHub Wiki
1、ActivityManagerService是什么时候启动的，有什么作用？
ActivityManagerService，简称AMS，服务端对象，负责系统中所有Activity的生命周期。
public final class SystemServer {
//zygote的主入口
public static void main(String[] args) {
new SystemServer().run();
}
public SystemServer() {
// Check for factory test mode.
mFactoryTestMode = FactoryTest.getMode();
}
private void run() {
...ignore some code...
//加载本地系统服务库，并进行初始化
System.loadLibrary("android_servers");
nativeInit();
// 创建系统上下文
createSystemContext();
//初始化SystemServiceManager对象，下面的系统服务开启都需要调用SystemServiceManager.startService(Class<T>)，这个方法通过反射来启动对应的服务
mSystemServiceManager = new SystemServiceManager(mSystemContext);
//开启服务
try {
startBootstrapServices();
startCoreServices();
startOtherServices();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
}
...ignore some code...
}
//初始化系统上下文对象mSystemContext，并设置默认的主题,mSystemContext实际上是一个ContextImpl对象。调用ActivityThread.systemMain()的时候，会调用ActivityThread.attach(true)，而在attach()里面，则创建了Application对象，并调用了Application.onCreate()。
private void createSystemContext() {
ActivityThread activityThread = ActivityThread.systemMain();
mSystemContext = activityThread.getSystemContext();
mSystemContext.setTheme(android.R.style.Theme_DeviceDefault_Light_DarkActionBar);
}
//在这里开启了几个核心的服务，因为这些服务之间相互依赖，所以都放在了这个方法里面。
private void startBootstrapServices() {
...ignore some code...
//初始化ActivityManagerService
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
//初始化PowerManagerService，因为其他服务需要依赖这个Service，因此需要尽快的初始化
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
// 现在电源管理已经开启，ActivityManagerService负责电源管理功能
mActivityManagerService.initPowerManagement();
// 初始化DisplayManagerService
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
//初始化PackageManagerService
mPackageManagerService = PackageManagerService.main(mSystemContext, mInstaller,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
...ignore some code...
}
}
ActivityManagerService进行初始化的时机很明确，就是在SystemServer进程开启的时候，就会初始化ActivityManagerService。从下面的代码中可以看到
2、应用是如何与ActivityManagerService通信的？
客户端：ActivityManagerProxy =====>Binder驱动=====> ActivityManagerService：服务器
3、ActiityManagerService是如何与应用通信的？
客户端：ApplicationThread <=====Binder驱动<===== ApplicationThreadProxy：服务器
4、Activity消息循环是怎么时候创建的？
是在ActivityThread初始化的时候，就已经创建消息循环了，所以在主线程里面创建Handler不需要指定Looper，而如果在其他线程使用Handler，则需要单独使用Looper.prepare()和Looper.loop()创建消息循环。
public static void main(String[] args) {
...ignore some code...
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
AsyncTask.init();
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
...ignore some code...
}
5、一个app的程序入口在哪里？
是ActivityThread.main()。
6、应用application是什么时候创建的？
也是在ActivityThread.main()的时候，再具体点呢，就是在thread.attach(false)的时候。
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
//普通App进这里
if (!system) {
...ignore some code...
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
// Ignore
}
} else {
//这个分支在SystemServer加载的时候会进入，通过调用
// private void createSystemContext() {
// ActivityThread activityThread = ActivityThread.systemMain()；
//}
// public static ActivityThread systemMain() {
// if (!ActivityManager.isHighEndGfx()) {
// HardwareRenderer.disable(true);
// } else {
// HardwareRenderer.enableForegroundTrimming();
// }
// ActivityThread thread = new ActivityThread();
// thread.attach(true);
// return thread;
// }
}
}
这里需要关注的就是mgr.attachApplication(mAppThread)，这个就会通过Binder调用到AMS里面对应的方法
@Override
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
然后就是
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat, getCommonServicesLocked(),
mCoreSettingsObserver.getCoreSettingsLocked());
}
thread是IApplicationThread，实际上就是ApplicationThread在服务端的代理类ApplicationThreadProxy，然后又通过IPC就会调用到ApplicationThread的对应方法
private class ApplicationThread extends ApplicationThreadNative {
public final void bindApplication(String processName, ApplicationInfo appInfo,
List<ProviderInfo> providers, ComponentName instrumentationName,
ProfilerInfo profilerInfo, Bundle instrumentationArgs,
IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection, int debugMode,
boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,
Configuration config, CompatibilityInfo compatInfo, Map<String, IBinder> services,
Bundle coreSettings) {
...ignore some code...
AppBindData data = new AppBindData();
data.processName = processName;
data.appInfo = appInfo;
data.providers = providers;
data.instrumentationName = instrumentationName;
data.instrumentationArgs = instrumentationArgs;
data.instrumentationWatcher = instrumentationWatcher;
data.instrumentationUiAutomationConnection = instrumentationUiConnection;
data.debugMode = debugMode;
data.enableOpenGlTrace = enableOpenGlTrace;
data.restrictedBackupMode = isRestrictedBackupMode;
data.persistent = persistent;
data.config = config;
data.compatInfo = compatInfo;
data.initProfilerInfo = profilerInfo;
sendMessage(H.BIND_APPLICATION, data);
}
}
我们需要关注的其实就是最后的sendMessage()，里面有函数的编号H.BIND_APPLICATION，然后这个Messge会被H这个Handler处理
private class H extends Handler {
...ignore some code...
public static final int BIND_APPLICATION = 110;
...ignore some code...
public void handleMessage(Message msg) {
switch (msg.what) {
...ignore some code...
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
...ignore some code...
}
}
最后就在下面这个方法中，完成了实例化，拨那个企鹅通过mInstrumentation.callApplicationOnCreate实现了onCreate()的调用。
private void handleBindApplication(AppBindData data) {
try {
...ignore some code...
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
...ignore some code...
try {
mInstrumentation.onCreate(data.instrumentationArgs);
}
catch (Exception e) {
}
try {
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) { }
} finally {
StrictMode.setThreadPolicy(savedPolicy);
}
}
data.info是一个LoadeApk对象。
LoadeApk.data.info.makeApplication()
public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
if (mApplication != null) {
return mApplication;
}
Application app = null;
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals("android")) {
initializeJavaContextClassLoader();
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} catch (Exception e) { }
mActivityThread.mAllApplications.add(app);
mApplication = app;
//传进来的是null，所以这里不会执行，onCreate在上一层执行
if (instrumentation != null) {
try {
instrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
}
}
...ignore some code...
}
return app;
}
所以最后还是通过Instrumentation.makeApplication()实例化的，这个老板娘真的很厉害呀！
static public Application newApplication(Class<?> clazz, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
Application app = (Application)clazz.newInstance();
app.attach(context);
return app;
}
而且通过反射拿到Application对象之后，直接调用attach()，所以attach()调用是在onCreate()之前的。