1.概述
基于Android9.0（SDK 28）源碼。
關(guān)鍵類：
ActivityThred
ApplicationThread
ActivityManagerService
ProcessRecord 進程信息
ActivityRecord Activity信息
ActivityStack
ActivityStackSupervisor
LoadApk
2.Activity類中流程分析
2.1 Activity->startActivity()
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
//startActivity(Intent)：requestCode是-1了
startActivityForResult(intent, -1); //2.2 Activity->startActivityForResult()
}
}
2.2 Activity->startActivityForResult()
//requestCode=-1
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, Bundle options) {
...
//轉(zhuǎn)調(diào)到Instrumentation的execStartActivity()
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(this, mMainThread.getApplicationThread(), mToken,
this, intent, requestCode, options);
...
}
- mMainThread.getApplicationThread():
mMainThread是ActivityThread類型的實例,getApplicationThread獲取的是ActivityThread的內(nèi)部類ApplicationThread類型的實例，ApplicationThread實際上也是IPC調(diào)用,對應(yīng)的AIDL文件是IApplicationThread.aidl。
3 Instrumentation類中流程
Activity->startActivityForResult()方法中轉(zhuǎn)調(diào)到了Instrumentation->execStartActivity():
public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
...
//result是執(zhí)行啟動后的結(jié)果,類似于錯誤碼,標記不同的錯誤類型
//從這里調(diào)用了ActivityManagerService的startActivity()，是ipc調(diào)用，ActivityManager.getService()是通過單例模式實現(xiàn)的
int result = ActivityManager.getService().startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
//根據(jù)AMS啟動Activity的result值，進行錯誤的處理，如果啟動失敗會拋出各種類型的異常，成功則直接return
checkStartActivityResult(result, intent);
}
public class ActivityManagerService extends IActivityManager.Stub implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
...
}
- ActivityManager.getService().startActivity()這個調(diào)用，是將whoThread（ActivityThread.ApplicationThread）接口引用傳到了AMS中。
- ActivityManager.getService()實際上獲取的是AMS的實例。
4 轉(zhuǎn)到SystemServer進程中：ActivityManagerService->startActivity()
AMS中startActivity()最后會轉(zhuǎn)調(diào)到startActivityAsUser():
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, boolean validateIncomingUser) {
...
//這里先轉(zhuǎn)調(diào)ActivityStartController進行userId檢查
userId = mActivityStartController.checkTargetUser(userId, validateIncomingUser, Binder.getCallingPid(),
Binder.getCallingUid(), "startActivityAsUser");
//又轉(zhuǎn)調(diào)到ActivityStarter的execute()方法
return mActivityStartController.obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
.setCallingPackage(callingPackage)
.setResolvedType(resolvedType)
.setResultTo(resultTo)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setStartFlags(startFlags)
.setProfilerInfo(profilerInfo)
.setActivityOptions(bOptions)
.setMayWait(userId) //mRequest.mayWait = true;會直接將mayWait標記為true
.execute();
}
2.5 ActivityStarter->execute()，會繼續(xù)調(diào)用到ActivityStarter->startActivityMayWait()方法
- 2.5.1 ActivityStarter->startActivityMayWait()
private 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, SafeActivityOptions options, boolean ignoreTargetSecurity,
int userId, TaskRecord inTask, String reason,
boolean allowPendingRemoteAnimationRegistryLookup) {
...
//轉(zhuǎn)調(diào)startActivity()
int res = startActivity(caller, intent, ephemeralIntent, resolvedType, aInfo, rInfo,
voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid,
callingUid, callingPackage, realCallingPid, realCallingUid, startFlags, options,
ignoreTargetSecurity, componentSpecified, outRecord, inTask, reason,
allowPendingRemoteAnimationRegistryLookup);
...
}
- 2.5.2 ActivityStarter->startActivity()：
private int startActivity(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,
SafeActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
ActivityRecord[] outActivity, TaskRecord inTask, String reason,
boolean allowPendingRemoteAnimationRegistryLookup) {
mLastStartActivityResult = startActivity(caller, intent, ephemeralIntent, resolvedType,
aInfo, rInfo, voiceSession, voiceInteractor, resultTo, resultWho, requestCode,
callingPid, callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,
options, ignoreTargetSecurity, componentSpecified, mLastStartActivityRecord,
inTask, allowPendingRemoteAnimationRegistryLookup);
return getExternalResult(mLastStartActivityResult);
}
- 2.5.3 ActivityStarter->startActivity()：
private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,...) {
//這里startActivity()傳入的Bundle類型的option參數(shù)由ActivityOptions進行管理了
final Bundle verificationBundle = options != null ? options.popAppVerificationBundle() : null;
ProcessRecord callerApp = null;
return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags,
true /* doResume */, checkedOptions, inTask, outActivity);
- 2.5.4 ActivityStarter->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;
result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor, startFlags, doResume, options, inTask, outActivity);
return result;
}
- 2.5.5 ActivityStarter-> startActivityUnchecked():
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity) {
if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
&& (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
newTask = true;
result = setTaskFromReuseOrCreateNewTask(taskToAffiliate, topStack);
} else if (mSourceRecord != null) {
result = setTaskFromSourceRecord();
} else if (mInTask != null) {
result = setTaskFromInTask();
} else {
setTaskToCurrentTopOrCreateNewTask();
}
if (mDoResume) {
final ActivityRecord topTaskActivity = mStartActivity.getTask().topRunningActivityLocked();
if (!mTargetStack.isFocusable()
|| (topTaskActivity != null && topTaskActivity.mTaskOverlay
&& mStartActivity != topTaskActivity)) {
mTargetStack.ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
mService.mWindowManager.executeAppTransition();
} else {
//流程轉(zhuǎn)調(diào)到ActivityStackSupervisor類的resumeFocusedStackTopActivity()方法
mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
mOptions);
}
}
}
- mSupervisor:ActivityStackSupervisor,Activity棧的管理者。
3.ActivityStackSupervisor中的流程
- 3.1 ActivityStackSupervisor::resumeFocusedStackTopActivityLocked():
boolean resumeFocusedStackTopActivityLocked(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
//獲取要啟動Activity所在棧的棧頂?shù)牟皇翘幱谕Ｖ範顟B(tài)的Activiy的ActivityRecord
final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
if (r == null || !r.isState(RESUMED)) {
mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
} else if (r.isState(RESUMED)) {
// Kick off any lingering app transitions form the MoveTaskToFront operation.
mFocusedStack.executeAppTransition(targetOptions);
}
return false;
}
4.ActivityStack中的流程
4.1ActivityStack->resumeTopActivityUncheckedLocked()
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
...
boolean result = false;
result = resumeTopActivityInnerLocked(prev, options);
return result;
}
4.2ActivityStack->resumeTopActivityInnerLocked()
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);
if (next.app != null && next.app.thread != null) {
mStackSupervisor.startSpecificActivityLocked(next, true, true);
}
}
4.3 ActivityStackSupervisor->startSpecificActivityLocked()
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
//用進程名拿到ProcessRecord實例
ProcessRecord app = mService.getProcessRecordLocked(r.processName, r.info.applicationInfo.uid, true);
if (app != null && app.thread != null) {
realStartActivityLocked(r, app, andResume, checkConfig);
}
}
4.4 ActivityStackSupervisor->realStartActivityLocked()
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume,
boolean checkConfig) throws RemoteException {
final TaskRecord task = r.getTask();
final ActivityStack stack = task.getStack();
// 創(chuàng)建一個啟動Activity的事務(wù),并且將applicationThread傳給ClienTransaction類中
final ClientTransaction clientTransaction = ClientTransaction.obtain(app.thread, r.appToken);
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, app.repProcState,
r.icicle, r.persistentState, results, newIntents,
mService.isNextTransitionForward(), profilerInfo));
final ActivityLifecycleItem lifecycleItem;
if (andResume) {
lifecycleItem = ResumeActivityItem.obtain(mService.isNextTransitionForward());
} else {
lifecycleItem = PauseActivityItem.obtain();
}
clientTransaction.setLifecycleStateRequest(lifecycleItem);
//1.以事務(wù)的形式轉(zhuǎn)發(fā)
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
}
- 1.這里的mService就是AMS實例，mService.getLifecycleManager()獲取的mLifecycleManager是在ActivityManagerService的構(gòu)造函數(shù)中new出來的
4.5 ClientLifecycleManager->scheduleTransaction()
//ClientLifecycleManager::scheduleTransaction()，ClientTransaction實現(xiàn)了Parcelable接口，所以支持跨進程傳輸
void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
final IApplicationThread client = transaction.getClient();
//ClinetTransaction會直接調(diào)用IApplicationThread的scheduleTransaction(ClinetTrasaction)，
//IApplicationThread的實現(xiàn)類是ActivityThread的內(nèi)部類ApplicationThread
transaction.schedule();
if (!(client instanceof Binder)) {
transaction.recycle();
}
}
- ClientTransaction
//ActivityStackSupervisor->realStartActivityLocked()中： ClientTransaction.obtain(app.thread, r.appToken)的app.thread對象
private IApplicationThread mClient;
public IApplicationThread getClient() {
return mClient;
}
public void schedule() throws RemoteException {
mClient.scheduleTransaction(this);
}
ApplicationThread->scheduleTransaction()
@Override
public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {
//ActivityThread中并沒有scheduleTransaction()方法實現(xiàn)代碼，
//其實是調(diào)用了父類ClientTransactionHandler::scheduleTransaction()方法
ActivityThread.this.scheduleTransaction(transaction);
}
ClientTransactionHandler::scheduleTransaction()方法
//ActivityThread是繼承自ClientTransactionHandler
class ActivityThread extends ClientTransactionHandler {}
void scheduleTransaction(ClientTransaction transaction) {
transaction.preExecute(this);
//將事務(wù)發(fā)到H(Handler)了
sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);
}
//H::handleMessgae()
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
//執(zhí)行了TransactionExecutor的execute方法，會執(zhí)行一個executeCallbacks()，
//然后調(diào)用cycleToPath()，最終會調(diào)用到performLifecycleSequence()
mTransactionExecutor.execute(transaction);
if (isSystem()) {
transaction.recycle();
}
break;
}
TransactionExecutor::execute()->executeLifecycleState()->cycleToPath()->performLifecycleSequence()
//performLifecycleSequence(),通過TransactionHandler就可以回調(diào)到ActivityThread的各種生命周期方法了
private void performLifecycleSequence(ActivityClientRecord r, IntArray path) {
final int size = path.size();
for (int i = 0, state; i < size; i++) {
state = path.get(i);
log("Transitioning to state: " + state);
switch (state) {
case ON_CREATE:
//調(diào)用ActivityThread的handleLaunchActivity，會進一步調(diào)用創(chuàng)建Activity實例，回調(diào)Activity的onCreate方法等
mTransactionHandler.handleLaunchActivity(r, mPendingActions,null);
break;
case ON_START:
//onStart()
mTransactionHandler.handleStartActivity(r, mPendingActions);
break;
case ON_RESUME:
//onResume()
mTransactionHandler.handleResumeActivity(r.token, false ,r.isForward, "LIFECYCLER_RESUME_ACTIVITY");
break;
case ON_PAUSE:
//onPause()
mTransactionHandler.handlePauseActivity(r.token, false , false , 0 ,
mPendingActions, "LIFECYCLER_PAUSE_ACTIVITY");
break;
case ON_STOP:
//onStop()
mTransactionHandler.handleStopActivity(r.token, false,
0, mPendingActions, false ,"LIFECYCLER_STOP_ACTIVITY");
break;
case ON_DESTROY:
//onDestroy()
mTransactionHandler.handleDestroyActivity(r.token, false ,
0, false ,"performLifecycleSequence. cycling to:" + path.get(size - 1));
break;
case ON_RESTART:
//onRestart()
mTransactionHandler.performRestartActivity(r.token, false );
break;
default:
throw new IllegalArgumentException("Unexpected lifecycle state: " + state);
}
}
從上述代碼可以看出，ClientTrasactionHandler最后通過TransactionExecutor真正發(fā)起Activity的各種生命周期方法的調(diào)用，如果在創(chuàng)建Activity實例時，Application實例未被創(chuàng)建，就會先創(chuàng)建Application實例，二者都是通過類全限定名和ClassLoader完成實例的創(chuàng)建。
ActivityThread中的啟動流程
- Activity啟動的核心方法： ActivityThread::performLaunchActivity()
//android.app.ActivityThread#performLaunchActivity
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
//這個Context是Activity級別的
ContextImpl appContext = createBaseContextForActivity(r);
//1.使用Instrumentation和ClassLoader采用反射方式創(chuàng)建Activity實例
Activity activity = null;
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
//2.獲取Application實例，如果為null同樣會同樣使用反射和classsLoader創(chuàng)建實例，是使用Instrumentation創(chuàng)建的，具體實現(xiàn)代碼在：android.app.LoadedApk#makeApplication()
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
...
//3.初始化Activity的關(guān)鍵參數(shù)
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);
//4.Activity，Application都創(chuàng)建完成了，轉(zhuǎn)調(diào)Activity的onCreate()方法
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
}
ContextImpl的創(chuàng)建時機，是怎么和Activity關(guān)聯(lián)起來的？Activity重寫的getSystemService()方法最終中間是由ContextImpl轉(zhuǎn)調(diào)的，但是沒有看大ContextImpl是怎么傳到Activity內(nèi)的。
//android.app.ActivityThread#performLaunchActivity()中有一段代碼是這樣：
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
ContextImpl appContext = createBaseContextForActivity(r);
...
//這里將創(chuàng)建的ContextImpl實例傳給了Activity
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);
}
Activity對象的創(chuàng)建過程
在ActivityThread::performLaunchActivity()中，調(diào)用了Instrumentation#newActivity()方法，這個就是開始創(chuàng)建Activity實例的開始。
//android.app.Instrumentation#newActivity(java.lang.ClassLoader, java.lang.String, android.content.Intent)
public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
String pkg = intent != null && intent.getComponent() != null
? intent.getComponent().getPackageName() : null;
return getFactory(pkg).instantiateActivity(cl, className, intent);
}
AppComponentFactory->instantiateActivity:直接通過反射創(chuàng)建Activity對象
public @NonNull Activity instantiateActivity(@NonNull ClassLoader cl, @NonNull String className,
@Nullable Intent intent)
throws InstantiationException, IllegalAccessException, ClassNotFoundException {
return (Activity) cl.loadClass(className).newInstance();
}
Application對象的創(chuàng)建過程:LoadApk->makeApplication()
public Application makeApplication(boolean forceDefaultAppClass, Instrumentation instrumentation) {
if (mApplication != null) {
return mApplication;
}
Application app = null;
String appClass = mApplicationInfo.className;
//如果className為null就默認為android.app.Application
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals("android")) {
initializeJavaContextClassLoader(); //檢查創(chuàng)建PathClassLoader對象
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
}
參考文獻
[1]http://gityuan.com/2016/03/12/start-activity/
[2]Android開發(fā)藝術(shù)探索，任玉剛
[3]Android進階解密，劉望舒
