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Launcher的startActivity
桌面是Launcher进程的页面，从桌面点击图标启动app,实际是在Launcher启动另一个进程的Activity。首先我们在Launcher的main线程（即所谓UI线程）里调用startActivity，这个方法最终通过Instrumentation调用ActivityManagerProxy的startActivity方法，通过ActivityManagerProxy远程调用ActivityManagerService同名方法。而后System进程会在告知Launcher进程pauseActivity,所以不要在onpause方法中做耗时操作哦！
System的Process.main
如果被启动activity所依附的进程还没有启动，就会初始化该进程。实际的实现是zygote进程与system_server之间通过socket通信，要创建进程时，system_server 进程里通过往socket写入消息，zygote接收到消息后fork出一个进程，最终会调用ActivityThread的main函数。
应用进程的ActivityThread.main
public static void main(String[] args) {
Looper.prepareMainLooper();
ActivityThread thread =new ActivityThread();
thread.attach(false);
Looper.loop();
}
创建ActivityThread实例，生命Looper开始loop,并调用attach，还会创建 ApplicationThread 对象作为匿名Binder服务端用以跟system_server进程通信，在thread.attach(false) 中通过AMP把 这个对象注册到AMS。
应用进程的bindApplication
通过Binder机制远端调用bindApplication方法实际调用到ActivityThread的handleBindApplication方法。
// Allow disk access during application and provider setup. This could
// block processing ordered broadcasts, but later processing would
// probably end up doing the same disk access.
final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
//实例化Application
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if (!data.restrictedBackupMode) {
if (!ArrayUtils.isEmpty(data.providers)) {
//初始化ContentProvider
installContentProviders(app, data.providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
try {
mInstrumentation.onCreate(data.instrumentationArgs);
}
catch (Exception e) {
throw new RuntimeException(
"Exception thrown in onCreate() of "
+ data.instrumentationName + ": " + e.toString(), e);
}
try {
//调用Application.onCreate
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
} finally {
StrictMode.setThreadPolicy(savedPolicy);
}
在其中完成了Application的实例化，ContentProvider的实例化Application的onCreate生命周期。
应用进程的performLaunchActivity方法
AMS里面 远程调用ActivityThread的bindApplication同时调用了其scheduleLaunchActivity方法实际调用到performLaunchActivity
Activity activity = null;
try {
//反射实例化Activity
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to instantiate activity " + component
+ ": " + e.toString(), e);
}
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
... ...
if (activity != null) {
//ContextImpl实例
Context appContext = createBaseContextForActivity(r, activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mCompatConfiguration);
if (r.overrideConfig != null) {
config.updateFrom(r.overrideConfig);
}
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
+ r.activityInfo.name + " with config " + config);
Window window = null;
if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
window = r.mPendingRemoveWindow;
r.mPendingRemoveWindow = null;
r.mPendingRemoveWindowManager = null;
}
//Activity的很多功能会委托给ContextImpl实例实现
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window);
if (customIntent != null) {
activity.mIntent = customIntent;
}
r.lastNonConfigurationInstances = null;
activity.mStartedActivity = false;
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
activity.setTheme(theme);
}
activity.mCalled = false;
//调用Activity.onCreate
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
... ...
//Activity.onStart
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
///Activity.onRestoreInstanceState
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state != null || r.persistentState != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
r.persistentState);
}
} else if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
在这个方法中Instrumentation反射创建Activity
调用activity的attach,oncreate,onstart方法。
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