早就想搞一篇这样的启动过程的文章，但是局限于自己能力有限一直没有敢写，今天要写是因为最近一直在研究这个启动流程，感觉自己已经研究明白了，可以写出来加深一下记忆了。这是用的sdk26的源码也就是Android 8 的源码。
先上Activity的继承关系，如果想看到这个界面可以用快捷键Ctrl + h，然后双击打开这个Activity，开始神奇的源码之旅。
我们都会用startActivity（Intent intent）来启动Activity,这个startActivity有很两个名字一样的重载方法，不过最后都会调用
startActivityForResult方法，上代码：
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) { //这个地方我们只研究mParent == null的情况，因为mParent != null 是很早以前的版本内容了（大概是3.1） //现在这个MParent会是null的 if (mParent == null) { options = transferSpringboardActivityOptions(options); Instrumentation.ActivityResult ar = // 这个地方调用Instrumentation中的execStartActivity方法 mInstrumentation.execStartActivity( this, mMainThread.getApplicationThread(), mToken, this, intent, requestCode, options); if (ar != null) { //mMainThread是ApplicationThread对象 mMainThread.sendActivityResult( mToken, mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData()); } if (requestCode >= 0) { mStartedActivity = true; } cancelInputsAndStartExitTransition(options); // TODO Consider clearing/flushing other event sources and events for child windows } else { if (options != null) { mParent.startActivityFromChild(this, intent, requestCode, options); } else { // Note we want to go through this method for compatibility with // existing applications that may have overridden it. mParent.startActivityFromChild(this, intent, requestCode); } } }
下面看下Instrumentation中的execStartActivity方法代码
public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) { IApplicationThread whoThread = (IApplicationThread) contextThread; Uri referrer = target != null ? target.onProvideReferrer() : null; if (referrer != null) { intent.putExtra(Intent.EXTRA_REFERRER, referrer); } ... 省略代码 try { intent.migrateExtraStreamToClipData(); intent.prepareToLeaveProcess(who); int result = ActivityManager.getService()//这个地方是得到ActivityManagerService .startActivity(whoThread, who.getBasePackageName(), intent, intent.resolveTypeIfNeeded(who.getContentResolver()), token, target != null ? target.mEmbeddedID : null, requestCode, 0, null, options); checkStartActivityResult(result, intent); } catch (RemoteException e) { throw new RuntimeException("Failure from system", e); } return null; }
这个地方来看下这个ActivityManager.getService()方法，就是一个单例模式获得对象
public static IActivityManager getService() { return IActivityManagerSingleton.get(); } private static final Singleton<IActivityManager> IActivityManagerSingleton = new Singleton<IActivityManager>() { @Override protected IActivityManager create() { final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE); final IActivityManager am = IActivityManager.Stub.asInterface(b); return am; } };
这个地方需要介绍下这个IActivityManager，通过它的创建可以知道是一个Binder机制与后台服务进行交互的对象，这个服务对象就是ActivityManagerService现在就让我进入这个ActivityManagerService中找到前面调用的startActivity方法。
@Override public final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) { return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, UserHandle.getCallingUserId()); }
@Override public final int startActivityAsUser(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) { enforceNotIsolatedCaller("startActivity"); userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId, false, ALLOW_FULL_ONLY, "startActivity", null); // TODO: Switch to user app stacks here. return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent, resolvedType, null, null, resultTo, resultWho, requestCode, startFlags, profilerInfo, null, null, bOptions, false, userId, null, null, "startActivityAsUser"); }
竟然进入了ActivityStarter这个类中了，我们就继续
final int startActivityMayWait(IApplicationThread caller, int callingUid, String callingPackage, Intent intent, String resolvedType, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, WaitResult outResult, Configuration globalConfig, Bundle bOptions, boolean ignoreTargetSecurity, int userId,IActivityContainer iContainer, TaskRecord inTask, String reason) { // Refuse possible leaked file descriptors ...省略代码 final ActivityRecord[] outRecord = new ActivityRecord[1]; int res = startActivityLocked(caller, intent, ephemeralIntent, resolvedType, aInfo, rInfo, voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid, callingUid, callingPackage, realCallingPid, realCallingUid, startFlags, options, ignoreTargetSecurity, componentSpecified, outRecord, container, inTask, reason); ...省略代码 mSupervisor.mActivityMetricsLogger.notifyActivityLaunched(res, outRecord[0]); return res; } }
int startActivityLocked(IApplicationThread caller, Intent intent, Intent ephemeralIntent, String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid, String callingPackage, int realCallingPid, int realCallingUid, int startFlags, ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity, ActivityStackSupervisor.ActivityContainer container, TaskRecord inTask, String reason) { if (TextUtils.isEmpty(reason)) { throw new IllegalArgumentException("Need to specify a reason."); } mLastStartReason = reason; mLastStartActivityTimeMs = System.currentTimeMillis(); mLastStartActivityRecord[0] = null; mLastStartActivityResult = startActivity(caller, intent, ephemeralIntent, resolvedType,aInfo, rInfo, voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid, callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,options, ignoreTargetSecurity, componentSpecified, mLastStartActivityRecord, container, inTask); if (outActivity != null) { // mLastStartActivityRecord[0] is set in the call to startActivity above. outActivity[0] = mLastStartActivityRecord[0]; } return mLastStartActivityResult; } 中间会经过好几个startActivity不过最后还是会走到下面的startActivity
private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask, ActivityRecord[] outActivity) { int result = START_CANCELED; try { mService.mWindowManager.deferSurfaceLayout(); // result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor, startFlags, doResume, options, inTask, outActivity); } finally { // If we are not able to proceed, disassociate the activity from the task. Leaving an // activity in an incomplete state can lead to issues, such as performing operations // without a window container. if (!ActivityManager.isStartResultSuccessful(result) && mStartActivity.getTask() != null) { mStartActivity.getTask().removeActivity(mStartActivity); } mService.mWindowManager.continueSurfaceLayout(); } postStartActivityProcessing(r, result, mSupervisor.getLastStack().mStackId, mSourceRecord,mTargetStack); return result; }
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask, ActivityRecord[] outActivity) { //....省略代码 if (mDoResume) { ...省略代码 } else { ...省略代码 mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity, mOptions); } } else { mTargetStack.addRecentActivityLocked(mStartActivity); } ...省略代码 return START_SUCCESS; }
在这个地方出了ActivityStarter这个类，进入ActivityStackSupervisor的resumeFocusedStackTopActivityLocked()
boolean resumeFocusedStackTopActivityLocked() { return resumeFocusedStackTopActivityLocked(null, null, null); } boolean resumeFocusedStackTopActivityLocked( ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) { if (targetStack != null && isFocusedStack(targetStack)) { // 这个地方进入ActivityStack的resumeTopActivityUnchecked方法 return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions); } final ActivityRecord r = mFocusedStack.topRunningActivityLocked(); if (r == null || r.state != RESUMED) { mFocusedStack.resumeTopActivityUncheckedLocked(null, null); } else if (r.state == RESUMED) { // Kick off any lingering app transitions form the MoveTaskToFront operation. mFocusedStack.executeAppTransition(targetOptions); } return false; }
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) { if (mStackSupervisor.inResumeTopActivity) { // Don't even start recursing. return false; } boolean result = false; try { // Protect against recursion. mStackSupervisor.inResumeTopActivity = true; result = resumeTopActivityInnerLocked(prev, options); } finally { mStackSupervisor.inResumeTopActivity = false; } mStackSupervisor.checkReadyForSleepLocked(); return result; }
private boolean resumeTopActivityInnerLocked(ActivityRecord prev,ActivityOptions options){ ...省略代码 ActivityStack lastStack = mStackSupervisor.getLastStack(); if (next.app != null && next.app.thread != null) { ...省略代码 } else { ...省略代码 mStackSupervisor.startSpecificActivityLocked(next, true, true); } if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked(); return true; }
这个地方又进入到ActivityStackSupervisor类中执行startSpecificActivityLocked方法
void startSpecificActivityLocked(ActivityRecord r,boolean andResume, boolean checkConfig){ ...省略代码 if (app != null && app.thread != null) { ..省略代码 realStartActivityLocked(r, app, andResume, checkConfig); return; } catch (RemoteException e) { ...省略代码 } } ...省略代码 }
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException { ...省略代码 // 这个地方就是进入ApplicationThread方法中执行scheduleLaunchActivity方法 app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken, System.identityHashCode(r), r.info, mergedConfiguration.getGlobalConfiguration(), mergedConfiguration.getOverrideConfiguration(), r.compat, r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results, newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo); ...省略代码 return true; }下面是ApplicationThread中的scheduleLaunchActivity的方法了
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) { updateProcessState(procState, false); 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; updatePendingConfiguration(curConfig); sendMessage(H.LAUNCH_ACTIVITY, r); }
这个ApplicationThread是ActivityThread的内部类，H是继承自Handler，也是ActivityThread的内部类。下面进入H这个类中的handleMessage中寻找这个消息对应的操作。
public void handleMessage(Message msg) { if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what)); switch (msg.what) { case LAUNCH_ACTIVITY: { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart"); final ActivityClientRecord r = (ActivityClientRecord) msg.obj; r.packageInfo = getPackageInfoNoCheck( r.activityInfo.applicationInfo, r.compatInfo); //走这个方法去寻找源码的奥秘吧 handleLaunchActivity(r, null, "LAUNCH_ACTIVITY"); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); } break;
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) { ...省略代码 Activity a = performLaunchActivity(r, customIntent); ...省略代码 }
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")"); // 1.通过ActivityClientRecord获得ActivityInfo ActivityInfo aInfo = r.activityInfo; if (r.packageInfo == null) { r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo, Context.CONTEXT_INCLUDE_CODE); } ComponentName component = r.intent.getComponent(); if (component == null) { component = r.intent.resolveActivity( mInitialApplication.getPackageManager()); r.intent.setComponent(component); } if (r.activityInfo.targetActivity != null) { component = new ComponentName(r.activityInfo.packageName, r.activityInfo.targetActivity); } //2.创建ContextImpl ContextImpl appContext = createBaseContextForActivity(r); Activity activity = null; try { java.lang.ClassLoader cl = appContext.getClassLoader(); // 3.利用Instrumentation创建一个Activity对象 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 { //4.创建一个Application对象，下面会有源码分析 Application app = r.packageInfo.makeApplication(false, mInstrumentation); if (localLOGV) Slog.v(TAG, "Performing launch of " + r); if (localLOGV) Slog.v( TAG, r + ": app=" + app + ", appName=" + app.getPackageName() + ", pkg=" + r.packageInfo.getPackageName() + ", comp=" + r.intent.getComponent().toShortString() + ", dir=" + r.packageInfo.getAppDir()); if (activity != null) { 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; } appContext.setOuterContext(activity); //5.通过attach方法让Activity与window进行绑定 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, r.configCallback); if (customIntent != null) { activity.mIntent = customIntent; } r.lastNonConfigurationInstances = null; checkAndBlockForNetworkAccess(); activity.mStartedActivity = false; int theme = r.activityInfo.getThemeResource(); if (theme != 0) { activity.setTheme(theme); } activity.mCalled = false; //调用onCreate前的准备 if (r.isPersistable()) { mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnCreate(activity, r.state); } if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onCreate()"); } r.activity = activity; r.stopped = true; if (!r.activity.mFinished) { activity.performStart(); r.stopped = false; } // 这里是调用onRestoreInstantState方法 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); } } //调用Activity的onCreate方法，进入Activity的生命周期 if (!r.activity.mFinished) { activity.mCalled = false; if (r.isPersistable()) { mInstrumentation.callActivityOnPostCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnPostCreate(activity, r.state); } if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onPostCreate()"); } } } r.paused = true; mActivities.put(r.token, r); } catch (SuperNotCalledException e) { throw e; } catch (Exception e) { if (!mInstrumentation.onException(activity, e)) { throw new RuntimeException( "Unable to start activity " + component + ": " + e.toString(), e); } } return activity; }
下面是makeApplication方法的源码
public Application makeApplication(boolean forceDefaultAppClass, Instrumentation instrumentation) { //如果有就直接返回，没有就去创建 if (mApplication != null) { return mApplication; } Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "makeApplication"); 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")) { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "initializeJavaContextClassLoader"); initializeJavaContextClassLoader(); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); } ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this); app = mActivityThread.mInstrumentation.newApplication( cl, appClass, appContext); appContext.setOuterContext(app); } catch (Exception e) { if (!mActivityThread.mInstrumentation.onException(app, e)) { Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); throw new RuntimeException( "Unable to instantiate application " + appClass + ": " + e.toString(), e); } } mActivityThread.mAllApplications.add(app); mApplication = app; if (instrumentation != null) { try { instrumentation.callApplicationOnCreate(app); } catch (Exception e) { if (!instrumentation.onException(app, e)) { Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); throw new RuntimeException( "Unable to create application " + app.getClass().getName() + ": " + e.toString(), e); } } } // Rewrite the R 'constants' for all library apks. SparseArray<String> packageIdentifiers = getAssets().getAssignedPackageIdentifiers(); final int N = packageIdentifiers.size(); for (int i = 0; i < N; i++) { final int id = packageIdentifiers.keyAt(i); if (id == 0x01 || id == 0x7f) { continue; } rewriteRValues(getClassLoader(), packageIdentifiers.valueAt(i), id); } Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); return app; }好了这个启动过程写了三个小时，真的是比较复杂，但是还是顺利的走完了。为自己点个赞。