之前Android应用程序进程的启动过程文章内有说过，当一个Android应用程序进程启动后，应用程序进程的入口就是ActivityThread类的main函数，ActivityThread的作用管理应用的主进程的执行，并根据AMS的要求，通过IApplicationThread接口负责调度和执行Activities和Broadcasts和其他操作，接下来这里会从main方法开始分析应用的启动流程;
以下源码基于rk3399_industry Android7.1.2
ActivityThread.main
总的来说这里主要是要向AMS发送一个进程启动完成通知，然后接收到回复在进行之后的步骤。
public final class ActivityThread {
final ApplicationThread mAppThread = new ApplicationThread();
public static void main(String[] args) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
....
//创建主线程的Looper对象
Looper.prepareMainLooper();
//创建ActivityThread实例，创建会同时在它内部创建一个ApplicationThread对象mAppThread
//mAppThread是一个Binder本地对象
//AMS就是通过该对象来和应用程序进程通信的
ActivityThread thread = new ActivityThread();
//调用attch函数向AMS发送一个启动完成的通知
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
//进入消息循环
Looper.loop();
....
}
private void attach(boolean system) {
//此时传入的system为false
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
//开启虚拟机的jit即时编译功能
ViewRootImpl.addFirstDrawHandler(new Runnable() {
@Override
public void run() {
ensureJitEnabled();
}
});
android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
//获得一个AMS的代理对象ActivityManagerProxy
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
//向AMS发送一个进程间通信请求
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
....
}
// 观察是否快接近heap的上限值
BinderInternal.addGcWatcher(new Runnable() {
@Override public void run() {
if (!mSomeActivitiesChanged) {
return;
}
Runtime runtime = Runtime.getRuntime();
long dalvikMax = runtime.maxMemory();
long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
//判断已用内存是否超过最大内存的3/4
if (dalvikUsed > ((3*dalvikMax)/4)) {
if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
+ " total=" + (runtime.totalMemory()/1024)
+ " used=" + (dalvikUsed/1024));
mSomeActivitiesChanged = false;
try {
//当已用内存超过最大内存的3/4,则请求释放内存空间
mgr.releaseSomeActivities(mAppThread);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
}
});
} else {
....
}
//添加dropbox日志到libcore
DropBox.setReporter(new DropBoxReporter());
....
}
}
接下来我们就会进入到AMS的代理对象ActivityManagerProxy的attachApplication函数向AMS发送一个进程间通信请求;
ActivityManagerProxy.attachApplication
frameworks/base/core/java/android/app/ActivityManagerNative.java
public abstract class ActivityManagerNative extends Binder implements IActivityManager{
....
class ActivityManagerProxy implements IActivityManager{
....
public void attachApplication(IApplicationThread app) throws RemoteException{
//将传入的参数写入data
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
//通过Binder代理对象mRemote向AMS发送类型为ATTACH_APPLICATION_TRANSACTION的进程间通信请求
//通知应用程序进程启动完成
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
}
}
ActivityManagerService.attachApplication
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
....
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
//AMS接收到应用程序进程启动完成
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
//执行启动应用的主Activity的操作
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
//保存进程pid的的对象，在应用程序进程创建完毕后会以pid为关键字，将对应的ProcessRecord对象存入进去
final SparseArray<ProcessRecord> mPidsSelfLocked = new SparseArray<ProcessRecord>();
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
//参数pid为应用程序进程的pid
ProcessRecord app;
//获得当前时间戳
long startTime = SystemClock.uptimeMillis();
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
//获得对应pid所对应的ProcessRecord对象赋值给app
app = mPidsSelfLocked.get(pid);
}
} else {
app = null;
}
....
final String processName = app.processName;
....
//对app对象进行初始化
//这个调用内会将app.thread = thread，即指向传入的ApplicationThread的代理对象
//这样AMS就可以通过这个thread和新创建的应用程序进程进行通信了
app.makeActive(thread, mProcessStats);
app.curAdj = app.setAdj = app.verifiedAdj = ProcessList.INVALID_ADJ;
app.curSchedGroup = app.setSchedGroup = ProcessList.SCHED_GROUP_DEFAULT;
app.forcingToForeground = null;
updateProcessForegroundLocked(app, false, false);
app.hasShownUi = false;
app.debugging = false;
app.cached = false;
app.killedByAm = false;
app.killed = false;
....
//这个PROC_START_TIMEOUT_MSG是一个判断是否启动超时的消息，在创建应用程序进程之前发送
//这里是删除该消息，因为应用程序已经在规定时间内启动起来了
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
....
try {
....
//完成前面的大量准备工作后，重点是这个方法，通知要启动的Application组件
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
....
} catch (Exception e) {
....
}
....
if (normalMode) {
try {
//在Application启动完毕后这里启动对应APP的主Activity
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
badApp = true;
}
}
//当Activity启动完成后启动所有运行在此进程的service
if (!badApp) {
try {
didSomething |= mServices.attachApplicationLocked(app, processName);
} catch (Exception e) {
....
badApp = true;
}
}
....
}
thread是一个ApplicationThreadProxy的Binder代理对象，所以这里最后会调用到ApplicationThreadProxy.bindApplication函数来向之前的应用程序进程发送一个进程间通信请求。
Application的启动
ApplicationThreadProxy.bindApplication
frameworks/base/core/java/android/app/ApplicationThreadNative.java
public abstract class ApplicationThreadNative extends Binder
implements IApplicationThread {
....
class ApplicationThreadProxy implements IApplicationThread {
....
public final void bindApplication(String packageName, ApplicationInfo info,
List<ProviderInfo> providers, ComponentName testName, ProfilerInfo profilerInfo,
Bundle testArgs, IInstrumentationWatcher testWatcher,
IUiAutomationConnection uiAutomationConnection, int debugMode,
boolean enableBinderTracking, boolean trackAllocation, boolean restrictedBackupMode,
boolean persistent, Configuration config, CompatibilityInfo compatInfo,
Map<String, IBinder> services, Bundle coreSettings) throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
data.writeString(packageName);
info.writeToParcel(data, 0);
data.writeTypedList(providers);
if (testName == null) {
data.writeInt(0);
} else {
data.writeInt(1);
testName.writeToParcel(data, 0);
}
if (profilerInfo != null) {
data.writeInt(1);
profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
data.writeInt(0);
}
data.writeBundle(testArgs);
data.writeStrongInterface(testWatcher);
data.writeStrongInterface(uiAutomationConnection);
data.writeInt(debugMode);
data.writeInt(enableBinderTracking ? 1 : 0);
data.writeInt(trackAllocation ? 1 : 0);
data.writeInt(restrictedBackupMode ? 1 : 0);
data.writeInt(persistent ? 1 : 0);
config.writeToParcel(data, 0);
compatInfo.writeToParcel(data, 0);
data.writeMap(services);
data.writeBundle(coreSettings);
mRemote.transact(BIND_APPLICATION_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
}
}
这部分就是将传入的参数写入Parcel对象data，然后通过Binder代理对象mRemote向前面的应用程序进程发送一个类行为BIND_APPLICATION_TRANSACTION的进程间通信请求。之后就又回到ApplicationThread.bindApplication函数。
ApplicationThread.bindApplication
frameworks/base/core/java/android/app/ActivityThread.java
public final class ActivityThread {
....
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 enableBinderTracking, boolean trackAllocation,
boolean isRestrictedBackupMode, boolean persistent, Configuration config,
CompatibilityInfo compatInfo, Map<String, IBinder> services, Bundle coreSettings) {
if (services != null) {
// 在服务管理器中设置服务缓存
ServiceManager.initServiceCache(services);
}
setCoreSettings(coreSettings);
//将传入的应用参数封装成data
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.enableBinderTracking = enableBinderTracking;
data.trackAllocation = trackAllocation;
data.restrictedBackupMode = isRestrictedBackupMode;
data.persistent = persistent;
data.config = config;
data.compatInfo = compatInfo;
data.initProfilerInfo = profilerInfo;
//发送了一个BIND_APPLICATION消息，之后来看消息处理
sendMessage(H.BIND_APPLICATION, data);
}
....
}
....
public void handleMessage(Message msg) {
switch (msg.what) {
....
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
//在跳转到handleBindApplication方法
handleBindApplication(data);
break;
....
}
}
//handleBindApplication函数非常的长，这里取重点部分讲解
private void handleBindApplication(AppBindData data) {
....
mBoundApplication = data;
....
/初始化一个ContextImpl对象appContext
final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);
//创建一个Application对象
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
try{
//调用callApplicationOnCreate，方法内部其实就是调用app.onCreate方法
//之后就进入了Application的生命周期的onCreate()方法了
//mInstrumentation是一个代理层，最终Apllication的创建，Activity的创建，以及生命周期都会经过这个对象去执行
mInstrumentation.callApplicationOnCreate(app);
....
} catch (Exception e) {
....
}
}
}
这部分callApplicationOnCreate比较简单，所以还是关注下如何创建的Application对象，data是一个类型为AppBindData的对象，其info变量的类行为LoadedApk，LoadedApk对象可以说是APK文件在内存中的表示，所以我们要来简单看下LoadedApk.makeApplication函数；
LoadedApk.makeApplication
frameworks/base/core/java/android/app/LoadedApk.java
public final class LoadedApk {
....
public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
if (mApplication != null) {
return mApplication;
}
Application app = null;
//获得Application的类名
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals("android")) {
initializeJavaContextClassLoader();
}
//创建上下文ContextImpl
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
//又回到了当前应用程秀进程的Instrumentation对象中
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} catch (Exception e) {
....
}
mActivityThread.mAllApplications.add(app);
mApplication = app;
....
return app;
}
}
Instrumentation.newApplication
frameworks/base/core/java/android/app/Instrumentation.java
public class Instrumentation {
....
public Application newApplication(ClassLoader cl, String className, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return newApplication(cl.loadClass(className), context);
}
static public Application newApplication(Class<?> clazz, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
//通过反射创建一个Application对象
Application app = (Application)clazz.newInstance();
//调用其attach方法，将app与context绑定
app.attach(context);
return app;
}
....
}
Application.attach & ContextWrapper.attachBaseContext
frameworks/base/core/java/android/app/Application.java
frameworks/base/core/java/android/content/ContextWrapper.java
public class Application extends ContextWrapper implements ComponentCallbacks2 {
....
final void attach(Context context) {
attachBaseContext(context);
mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
}
....
}
public class ContextWrapper extends Context {
....
protected void attachBaseContext(Context base) {
if (mBase != null) {
throw new IllegalStateException("Base context already set");
}
mBase = base;
}
....
}
这样就将Application和之前创建的上下文绑定起来了。
Activity和Service的启动
Application启动完成后，回到AMS的attachApplication函数内，之后会调用mStackSupervisor.attachApplicationLocked(app)和mServices.attachApplicationLocked(app,processName)分别启动Activity和Service;
Activity启动：ActivityStackSupervisor.attachApplicationLocked
frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
public final class ActivityStackSupervisor implements DisplayListener {
....
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
//获得进程名赋值给processName
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
//获得位于Activity栈顶端的ActivityRecord对象hr，与它对应的Activity组件就是要启动的Activity组件
ActivityRecord hr = stack.topRunningActivityLocked();
if (hr != null) {
//判断要启动的Activity的用户I(UID)和进程名是否与传入的ProcessRecord对象app的一致
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
//一致，代表Activity是在app中启动的，调用realStartActivityLocked启动Activity
if (realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (RemoteException e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
}
return didSomething;
}
....
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
....
//将传入的将要启动的Activity的ActivityRecord对象r的app设置为我们应用程序进程的app对象
r.app = app;
....
//idx<0代表r不在app的Activity组建列表中
int idx = app.activities.indexOf(r);
if (idx < 0) {
//将Activity添加进app的Activity组建列表activities中
app.activities.add(r);
}
....
try {
....
//一些准备工作
List<ResultInfo> results = null;
List<ReferrerIntent> newIntents = null;
if (andResume) {
results = r.results;
newIntents = r.newIntents;
}
....
if (r.isHomeActivity()) {
// Home进程是任务的根进程.
mService.mHomeProcess = task.mActivities.get(0).app;
}
....
//通知前面创建的应用程序进程启动Activity组件(即r所描述的Activity)
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo,r.task.taskId);
....
} catch (RemoteException e) {
....
}
....
return true;
}
}
在做了一些赋值和一些准备工作之后，就会开始通知前面创建的应用程序进程启动要创建的Activity，由源码可知app是ProcessRecord对象，而app.thread对应位ApplicationThreadProxy代理类，之后看对应的代码；
ApplicationThreadProxy.scheduleLaunchActivity
frameworks/base/core/java/android/app/ApplicationThreadNative.java
public abstract class ApplicationThreadNative extends Binder
implements IApplicationThread {
....
class ApplicationThreadProxy implements IApplicationThread {
....
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
boolean notResumed, boolean isForward, ProfilerInfo profilerInfo,int taskId) throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
intent.writeToParcel(data, 0);
data.writeStrongBinder(token);
data.writeInt(ident);
info.writeToParcel(data, 0);
curConfig.writeToParcel(data, 0);
if (overrideConfig != null) {
data.writeInt(1);
overrideConfig.writeToParcel(data, 0);
} else {
data.writeInt(0);
}
compatInfo.writeToParcel(data, 0);
data.writeString(referrer);
data.writeStrongBinder(voiceInteractor != null ? voiceInteractor.asBinder() : null);
data.writeInt(procState);
data.writeBundle(state);
data.writePersistableBundle(persistentState);
data.writeTypedList(pendingResults);
data.writeTypedList(pendingNewIntents);
data.writeInt(notResumed ? 1 : 0);
data.writeInt(isForward ? 1 : 0);
if (profilerInfo != null) {
data.writeInt(1);
profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
data.writeInt(0);
}
data.writeInt(taskId);
//调用Binder代理对象mRemote发送一个SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION的进程间通信请求
mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
....
}
....
}
ApplicationThread.scheduleLaunchActivity
frameworks/base/core/java/android/app/ActivityThread.java
public final class ActivityThread {
....
private class ApplicationThread extends ApplicationThreadNative {
....
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
boolean notResumed, boolean isForward, ProfilerInfo profilerInfo,int taskId_param) {
updateProcessState(procState, false);
//将要启动的Activity封装成ActivityClientRecord对象r
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.referrer = referrer;
r.voiceInteractor = voiceInteractor;
r.activityInfo = info;
r.compatInfo = compatInfo;
r.state = state;
r.persistentState = persistentState;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
r.profilerInfo = profilerInfo;
r.overrideConfig = overrideConfig;
r.taskId = taskId_param;
updatePendingConfiguration(curConfig);
//发送类型为LAUNCH_ACTIVITY，带着r的消息给创建的应用程序金层呢的消息队列处理
sendMessage(H.LAUNCH_ACTIVITY, r);
}
....
}
....
public void handleMessage(Message msg) {
switch (msg.what) {
....
case LAUNCH_ACTIVITY: {
//将发送来的obj转成ActivityClientRecord对象r
final ActivityClientRecord r = (ActivityClientRecord) msg.obj;
//调用getPackageInfoNoCheck获得一个LoadedApk对象保存在r.的成员函数packageInfo中
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo, r.compatInfo);
//进入函数handleLaunchActivity来启动Activity组件
handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");
} break;
....
}
}
....
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
....
// 确保我们使用最新的配置运行。
handleConfigurationChanged(null, null);
// 创建Activity前进行初始化
WindowManagerGlobal.initialize();
// performLaunchActivity函数会将Activity启动起来
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
//将Activity组件的状态设置为Resumed，代表它是系统当前显示的Activity
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
if (!r.activity.mFinished && r.startsNotResumed) {
//如果actvity没有finish，同时并不在resume状态，让Activity进入Pause状态，调用onPause生命方法。下方进入这个方法
performPauseActivityIfNeeded(r, reason);
....
}
} else {
....
}
}
....
//将Activity启动起来
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
....
//获得要启动的Activity组件的包名和类名赋值给component
ComponentName component = r.intent.getComponent();
....
Activity activity = null;
try {
//通过类加载器将component加载到内存中
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
//构造出一个对应Activity的实例activity
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
....
} catch (Exception e) {
....
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (activity != null) {
//创建一个ContextImpl对象，是创建的Activity的上下文环境
Context appContext = createBaseContextForActivity(r, activity);
....
//传入参数，调用attach进行Activity的初始化
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);
....
//通知Activity启动起来，callActivityOnCreate内部会调用Activity的生命周期onCreate()
mInstrumentation.callActivityOnCreate(activity, r.state);
//设置一些r的变量
....
}
}
....
//将r的token对象保存在ActivityThread的成员变量mActivities中
mActivities.put(r.token, r);
//r.token是一个Binder代理对象，只想了AMS内部的一个ActivityRecord对象
//这个ActivityRecord和对象r一样，都是用来描述启动的Activity的，只不过前者用于AMS，后者用于应用程序进程中。
} catch (SuperNotCalledException e) {
....
} catch (Exception e) {
....
}
return activity;
}
....
//将Activity组件的状态设置为Resumed，代表它是系统当前显示的Activity
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
//获得启动的Activity的ActivityClientRecord对象，并赋值给r
ActivityClientRecord r = mActivities.get(token);
//最后会调用到mInstrumentation.callActivityOnResume，之后Activity的onResume生命周期就会被调用了
r = performResumeActivity(token, clearHide, reason);
if (r != null) {
final Activity a = r.activity;
....
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient && !a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
}
} else if (!willBeVisible) {
....
}
....
}
// 通知AMS activity已经进入resume状态
if (reallyResume) {
try {
ActivityManagerNative.getDefault().activityResumed(token);
} catch (RemoteException ex) {
....
}
}
} else {
....
}
}
....
private void performPauseActivityIfNeeded(ActivityClientRecord r, String reason) {
if (r.paused) {
// 已经处于pause状态
return;
}
try {
r.activity.mCalled = false;
//调用Activity的onPause方法，函数内是调用Activity.performPause方法，最后会调用onPause生命周期
mInstrumentation.callActivityOnPause(r.activity);
r.activity.getComponentName().getClassName(), reason);
....
} catch (SuperNotCalledException e) {
....
} catch (Exception e) {
....
}
r.paused = true;
}
....
}
代码中为何需要获得一个LoadedApk对象，原因在于每一个Android应用程序都是打包在一个apk文件中，apk文件中包含了一个Android应用程序的所有资源，所以才需要在启动Activity时加载，为了可以访问到内部的资源文件。在ActivityThread类中就通过LoadedApk独享来描述加载的apk文件。
当我们加载完apk之后，便会进行初始化配置，创建要启动的Activity的实例，以此调用其attach，onCreate，onReume方法和生命周期，中间夹杂着一些上下文创建，参数配置等操作没有细说。
Service启动：ActiveServices.attachApplicationLocked
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java
public final class ActiveServices {
....
boolean attachApplicationLocked(ProcessRecord proc, String processName)
throws RemoteException {
boolean didSomething = false;
// 收集等待在此进程启动的所有服务。
if (mPendingServices.size() > 0) {
ServiceRecord sr = null;
try {
for (int i=0; i<mPendingServices.size(); i++) {
sr = mPendingServices.get(i);
//检查在mPendingServices中的Service组件是否需要在新创建的应用程序中启动
if (proc != sr.isolatedProc && (proc.uid != sr.appInfo.uid
|| !processName.equals(sr.processName))) {
continue;
}
//若需要启动Service，则先从mPendingServices把该成员删除
mPendingServices.remove(i);
i--;
proc.addPackage(sr.appInfo.packageName, sr.appInfo.versionCode,
mAm.mProcessStats);
//将要启动的Service启动起来
realStartServiceLocked(sr, proc, sr.createdFromFg);
....
}
} catch (RemoteException e) {
....
}
}
....
return didSomething;
}
....
// 启动Service
private final void realStartServiceLocked(ServiceRecord r,
ProcessRecord app, boolean execInFg) throws RemoteException {
....
//将ServiceRecord对象r的app设置为传入的app,这样就将r和app绑定起来。
//代表r所描述的Service是在app所描述的应用程序进程中启动的
r.app = app;
r.restartTime = r.lastActivity = SystemClock.uptimeMillis();
//将要创建的Service信息添加进app的services列表中
final boolean newService = app.services.add(r);
....
boolean created = false;
try {
....
//app.threa是类型为ApplicationThreadProxy对象，是一个Binder代理对象，指向应用程序进程ApplicationThread
//这里调用scheduleCreateService请求应用程序进程创建该service
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
r.postNotification();
created = true;
} catch (DeadObjectException e) {
....
} finally {
....
}
....
}
}
ApplicationThreadProxy.scheduleCreateService
frameworks/base/core/java/android/app/ApplicationThreadNative.java
public abstract class ApplicationThreadNative extends Binder
implements IApplicationThread {
....
class ApplicationThreadProxy implements IApplicationThread {
....
public final void scheduleCreateService(IBinder token, ServiceInfo info,
CompatibilityInfo compatInfo, int processState) throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
data.writeStrongBinder(token);
info.writeToParcel(data, 0);
compatInfo.writeToParcel(data, 0);
data.writeInt(processState);
try {
//发送一个类型为SCHEDULE_CREATE_SERVICE_TRANSACTION的进程间通信请求
mRemote.transact(SCHEDULE_CREATE_SERVICE_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
} catch (TransactionTooLargeException e) {
....
}
data.recycle();
}
....
}
....
}
ApplicationThread.scheduleCreateService
frameworks/base/core/java/android/app/ActivityThread.java
public final class ActivityThread {
....
public final void scheduleCreateService(IBinder token,
ServiceInfo info, CompatibilityInfo compatInfo, int processState) {
updateProcessState(processState, false);
//将要启动的Service的信息封装成一个CreateServiceData对象s
CreateServiceData s = new CreateServiceData();
s.token = token;
s.info = info;
s.compatInfo = compatInfo;
//发送了一个CREATE_SERVICE消息，之后来看消息处理
sendMessage(H.CREATE_SERVICE, s);
}
....
....
public void handleMessage(Message msg) {
switch (msg.what) {
....
case CREATE_SERVICE:
handleCreateService((CreateServiceData)msg.obj);
break;
....
}
}
....
private void handleCreateService(CreateServiceData data) {
....
//获得将要启动的Service组件所在应用程序的LoadedApk对象
LoadedApk packageInfo = getPackageInfoNoCheck(
data.info.applicationInfo, data.compatInfo);
Service service = null;
try {
//获得一个类加载器
java.lang.ClassLoader cl = packageInfo.getClassLoader();
//将要启动的Service加载到内存中，并创建其对应的一个实例service
service = (Service) cl.loadClass(data.info.name).newInstance();
} catch (Exception e) {
....
}
try {
....
//创建Service的一个上下文环境对象实例
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
//创建/获得一个应用程序对象app
Application app = packageInfo.makeApplication(false, mInstrumentation);
//通过上面传入和创建的参数初始化service
service.attach(context, this, data.info.name, data.token, app,
ActivityManagerNative.getDefault());
//初始化完成后调用Service的生命周期onCreate
service.onCreate();
//以CreateServiceData的token关键字，将service保存在ActivityThread类的成员变量mServices中
//与之前启动Activity类似，这里的token也是一个Binder代理对象
//指向了AMS内部的一个ServiceRecord对象，用来描述启动的Service
mServices.put(data.token, service);
....
} catch (Exception e) {
....
}
}
....
}
至此要启动的Service的onCreate就被调用了，启动完成
这里简单写了一个流程图如下：
activitythread_analysis.png
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