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歡迎指正靠汁，共同學(xué)習(xí)蜂大！
在上一篇文章<<Android 應(yīng)用進(jìn)程分裂分析>>中，已經(jīng)分析了一個(gè)應(yīng)用進(jìn)程是如何分裂出來的膀曾，這篇文章將會(huì)承接上一篇流程來分析一個(gè)Activity的啟動(dòng)流程县爬。
如何啟動(dòng)一個(gè)應(yīng)用？以PhoneWindowManager的啟動(dòng)Home為例：
void startDockOrHome() {
awakenDreams();
Intent dock = createHomeDockIntent();
if (dock != null) {
try {
mContext.startActivityAsUser(dock, UserHandle.CURRENT);
return;
} catch (ActivityNotFoundException e) {
}
}
mContext.startActivityAsUser(mHomeIntent, UserHandle.CURRENT);
}
通過Context.startActivity接口作為啟動(dòng)應(yīng)用的入口：
/**kitkat\frameworks\base\core\java\android\content\Context.java*/
public abstract void startActivity(Intent intent);
public void startActivityAsUser(Intent intent, UserHandle user) {
throw new RuntimeException("Not implemented. Must override in a subclass.");
}
public abstract void startActivity(Intent intent, Bundle options);
public void startActivityAsUser(Intent intent, Bundle options, UserHandle userId) {
throw new RuntimeException("Not implemented. Must override in a subclass.");
}
public abstract void startActivities(Intent[] intents);
Context是一個(gè)抽象類添谊，它的實(shí)現(xiàn)在ContextImpl類中：
@Override
public void startActivity(Intent intent) {
warnIfCallingFromSystemProcess();
startActivity(intent, null);
}
@Override
public void startActivity(Intent intent, Bundle options) {
warnIfCallingFromSystemProcess();
if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
throw new AndroidRuntimeException(
"Calling startActivity() from outside of an Activity "
+ " context requires the FLAG_ACTIVITY_NEW_TASK flag."
+ " Is this really what you want?");
}
mMainThread.getInstrumentation().execStartActivity(
getOuterContext(), mMainThread.getApplicationThread(), null,
(Activity)null, intent, -1, options);
}
Instrumentation是用在測(cè)試框架中的，但是它在Activity的啟動(dòng)中是占據(jù)巨大份量的察迟，Activity的啟動(dòng)和Instrumentation關(guān)系密不可分斩狱，但是在應(yīng)用中是不會(huì)使用到的：
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Fragment target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
if (mActivityMonitors != null) {
synchronized (mSync) {
final int N = mActivityMonitors.size();
for (int i=0; i<N; i++) {
final ActivityMonitor am = mActivityMonitors.get(i);
if (am.match(who, null, intent)) {
am.mHits++;
if (am.isBlocking()) {
return requestCode >= 0 ? am.getResult() : null;
}
break;
}
}
}
}
try {
intent.migrateExtraStreamToClipData();
intent.prepareToLeaveProcess();
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mWho : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
}
return null;
}
ActivityManagerNative是ActivityManagerService的BinderProxy端，這里涉及到Binder框架扎瓶，在我的另一篇文章中會(huì)分析：
public abstract class ActivityManagerNative extends Binder implements IActivityManager
{
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ActivityManagerProxy(obj);
}
...
class ActivityManagerProxy implements IActivityManager
{
public ActivityManagerProxy(IBinder remote)
{
mRemote = remote;
}
public IBinder asBinder()
{
return mRemote;
}
public int startActivity(IApplicationThread caller, String callingPackage, Intent intent,
String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, String profileFile,
ParcelFileDescriptor profileFd, Bundle options) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
data.writeString(callingPackage);
intent.writeToParcel(data, 0);
data.writeString(resolvedType);
data.writeStrongBinder(resultTo);
data.writeString(resultWho);
data.writeInt(requestCode);
data.writeInt(startFlags);
data.writeString(profileFile);
if (profileFd != null) {
data.writeInt(1);
profileFd.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} else {
data.writeInt(0);
}
if (options != null) {
data.writeInt(1);
options.writeToParcel(data, 0);
} else {
data.writeInt(0);
}
mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
reply.readException();
int result = reply.readInt();
reply.recycle();
data.recycle();
return result;
}
}
...
}
通過Binder機(jī)制的調(diào)用所踊，在ActivityManagerService中的處理如下：
@Override
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, options,
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 options, int userId) {
enforceNotIsolatedCaller("startActivity");
userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
false, ALLOW_FULL_ONLY, "startActivity", null);
// TODO: Switch to user app stacks here.
return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, options, userId, null, null);
}
ActivityStackSupervisor是和Activity堆棧相關(guān)的類，這里調(diào)用的層次有點(diǎn)多概荷，需要自己多寫多記錄下流程：
final int startActivityMayWait(IApplicationThread caller, int callingUid,
String callingPackage, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, String profileFile,
ParcelFileDescriptor profileFd, WaitResult outResult, Configuration config,
Bundle options, int userId) {
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
boolean componentSpecified = intent.getComponent() != null;
// Don't modify the client's object!
intent = new Intent(intent);
// Collect information about the target of the Intent.
ActivityInfo aInfo = resolveActivity(intent, resolvedType, startFlags,
profilerInfo, userId);
...
int res = startActivityLocked(caller, intent, resolvedType, aInfo,
voiceSession, voiceInteractor, resultTo, resultWho,
requestCode, callingPid, callingUid, callingPackage,
realCallingPid, realCallingUid, startFlags, options,
componentSpecified, null, container, inTask);
...
//針對(duì)需要返回返回result結(jié)果的處理部分
if (outResult != null) {
outResult.result = res;
if (res == ActivityManager.START_SUCCESS) {
mWaitingActivityLaunched.add(outResult);
do {
try {
mService.wait();
} catch (InterruptedException e) {
}
} while (!outResult.timeout && outResult.who == null);
} else if (res == ActivityManager.START_TASK_TO_FRONT) {
ActivityRecord r = stack.topRunningActivityLocked(null);
if (r.nowVisible && r.state == ActivityState.RESUMED) {
outResult.timeout = false;
outResult.who = new ComponentName(r.info.packageName, r.info.name);
outResult.totalTime = 0;
outResult.thisTime = 0;
} else {
outResult.thisTime = SystemClock.uptimeMillis();
mWaitingActivityVisible.add(outResult);
do {
try {
mService.wait();
} catch (InterruptedException e) {
}
} while (!outResult.timeout && outResult.who == null);
}
}
}
return res;
}
}
層次比較多秕岛，接下來分析startActivityLocked部分：
final int startActivityLocked(IApplicationThread caller,
Intent intent, String resolvedType, ActivityInfo aInfo, IBinder resultTo,
String resultWho, int requestCode,
int callingPid, int callingUid, String callingPackage, int startFlags, Bundle options,
boolean componentSpecified, ActivityRecord[] outActivity) {
...
doPendingActivityLaunchesLocked(false);
err = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, true, options, inTask);
if (err < 0) {
// If someone asked to have the keyguard dismissed on the next
// activity start, but we are not actually doing an activity
// switch... just dismiss the keyguard now, because we
// probably want to see whatever is behind it.
notifyActivityDrawnForKeyguard();
}
return err;
}
這一部分源碼校驗(yàn)了應(yīng)用權(quán)限，Intent攜帶的數(shù)據(jù)以及堆棧處理，以下這個(gè)函數(shù)有點(diǎn)多继薛，省略大部分后如下(注意在startActivityLocked傳的參數(shù)中doResume是true)：
final int startActivityUncheckedLocked(ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags,
boolean doResume, Bundle options, TaskRecord inTask) {
...
targetStack.mLastPausedActivity = null;
targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);
if (!launchTaskBehind) {
// Don't set focus on an activity that's going to the back.
mService.setFocusedActivityLocked(r);
}
return ActivityManager.START_SUCCESS;
}
這里又出現(xiàn)了ActivityStack對(duì)象修壕，這里可以把它理解為我們平時(shí)啟動(dòng)應(yīng)用后的一個(gè)Activity棧，其中有幾個(gè)常用的啟動(dòng)FLAG遏考，這里先分析startActivityLocked函數(shù)：
final void startActivityLocked(ActivityRecord r, boolean newTask,
boolean doResume, boolean keepCurTransition, Bundle options) {
...
//堆棧處理
task = r.task;
// Slot the activity into the history stack and proceed
if (DEBUG_ADD_REMOVE) Slog.i(TAG, "Adding activity " + r + " to stack to task " + task,
new RuntimeException("here").fillInStackTrace());
task.addActivityToTop(r);
task.setFrontOfTask();
...
if (doResume) {
mStackSupervisor.resumeTopActivitiesLocked(this, r, options);
}
}
之前提到過doResume在傳參時(shí)為True慈鸠，那么繼續(xù)分析resumeTopActivitiesLocked處理了什么：
boolean resumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,
Bundle targetOptions) {
if (targetStack == null) {
targetStack = getFocusedStack();
}
// Do targetStack first.
boolean result = false;
if (isFrontStack(targetStack)) {
result = targetStack.resumeTopActivityLocked(target, targetOptions);
}
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
final ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (stack == targetStack) {
// Already started above.
continue;
}
if (isFrontStack(stack)) {
stack.resumeTopActivityLocked(null);
}
}
}
return result;
}
可以看到這里是需要去啟動(dòng)堆棧中頂層的Activity：
final boolean resumeTopActivityLocked(ActivityRecord prev) {
return resumeTopActivityLocked(prev, null);
}
final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) {
if (inResumeTopActivity) {
// Don't even start recursing.
return false;
}
boolean result = false;
try {
// Protect against recursion.
inResumeTopActivity = true;
result = resumeTopActivityInnerLocked(prev, options);
} finally {
inResumeTopActivity = false;
}
return result;
}
又是各種中轉(zhuǎn)，讓人看的很暈灌具，真的快結(jié)束了：
final boolean resumeTopActivityInnerLocked(ActivityRecord prev, Bundle options) {
...
cancelInitializingActivities();
//這里會(huì)處理前一個(gè)Activity的狀態(tài)青团，比如從一個(gè)Activity A拉起另一個(gè)Activity B時(shí)，A會(huì)先入棧咖楣，并且回調(diào)OnPause
// Find the first activity that is not finishing.
ActivityRecord next = topRunningActivityLocked(null);
// Remember how we'll process this pause/resume situation, and ensure
// that the state is reset however we wind up proceeding.
final boolean userLeaving = mStackSupervisor.mUserLeaving;
mStackSupervisor.mUserLeaving = false;
final TaskRecord prevTask = prev != null ? prev.task : null;
if (next == null) {
// There are no more activities! Let's just start up the
// Launcher...
ActivityOptions.abort(options);
if (DEBUG_STATES) Slog.d(TAG, "resumeTopActivityLocked: No more activities go home");
if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
// Only resume home if on home display
final int returnTaskType = prevTask == null || !prevTask.isOverHomeStack() ?
HOME_ACTIVITY_TYPE : prevTask.getTaskToReturnTo();
return isOnHomeDisplay() &&
mStackSupervisor.resumeHomeStackTask(returnTaskType, prev);
}
...
} else {
// Whoops, need to restart this activity!
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
mWindowManager.setAppStartingWindow(
next.appToken, next.packageName, next.theme,
mService.compatibilityInfoForPackageLocked(
next.info.applicationInfo),
next.nonLocalizedLabel,
next.labelRes, next.icon, next.logo, next.windowFlags,
null, true);
}
if (DEBUG_SWITCH) Slog.v(TAG, "Restarting: " + next);
}
if (DEBUG_STATES) Slog.d(TAG, "resumeTopActivityLocked: Restarting " + next);
mStackSupervisor.startSpecificActivityLocked(next, true, true);
}
if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();
return true;
}
}
這又是一個(gè)比較復(fù)雜的函數(shù)督笆，涉及了當(dāng)前Activity和需要啟動(dòng)Activity堆棧的處理，以及和之關(guān)聯(lián)的Window的可視狀態(tài)等處理诱贿，涉及到不少狀態(tài)胖腾，google的工程師也對(duì)每一步都添加了注釋，還是相當(dāng)?shù)挠押谩?br> 簡化分析流程(應(yīng)用沒有啟動(dòng)過瘪松，只有一個(gè)Activity)咸作，最終還會(huì)調(diào)用startSpecificActivityLocked：
void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);
r.task.stack.setLaunchTime(r);
if (app != null && app.thread != null) {
try {
if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
|| !"android".equals(r.info.packageName)) {
// Don't add this if it is a platform component that is marked
// to run in multiple processes, because this is actually
// part of the framework so doesn't make sense to track as a
// separate apk in the process.
app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,
mService.mProcessStats);
}
realStartActivityLocked(r, app, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
}
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}
還是按簡化流程來分析，如果是沒有啟動(dòng)過包含這個(gè)Activity的應(yīng)用進(jìn)程宵睦，那么就可以直接分析startProcessLocked函數(shù)：
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
return startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingType,
hostingName, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
null /* crashHandler */);
}
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
//簡化分析省略
...
checkTime(startTime, "startProcess: stepping in to startProcess");
startProcessLocked(
app, hostingType, hostingNameStr, abiOverride, entryPoint, entryPointArgs);
checkTime(startTime, "startProcess: done starting proc!");
return (app.pid != 0) ? app : null;
}
private final void startProcessLocked(ProcessRecord app, String hostingType,
String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
//簡化分析 只看重點(diǎn)代碼
...
// Start the process. It will either succeed and return a result containing
// the PID of the new process, or else throw a RuntimeException.
boolean isActivityProcess = (entryPoint == null);
if (entryPoint == null) entryPoint = "android.app.ActivityThread";
checkTime(startTime, "startProcess: asking zygote to start proc");
Process.ProcessStartResult startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
app.info.dataDir, entryPointArgs);
checkTime(startTime, "startProcess: returned from zygote!");
...
}
終于看到核心代碼记罚，甚至有點(diǎn)熟悉，之前分析應(yīng)用進(jìn)程分裂時(shí)也看到過類似處理壳嚎，Android的Process類調(diào)用Start方法分裂出一個(gè)進(jìn)程來桐智。
看看源碼：
public static final ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int debugFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String[] zygoteArgs) {
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
debugFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}
注意，這里processClass是"android.app.ActivityThread"：
private static ProcessStartResult startViaZygote(final String processClass,
final String niceName,
final int uid, final int gid,
final int[] gids,
int debugFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String[] extraArgs)
throws ZygoteStartFailedEx {
...
return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
}
}
private static ProcessStartResult zygoteSendArgsAndGetResult(
ZygoteState zygoteState, ArrayList<String> args)
throws ZygoteStartFailedEx {
try {
/**
* See com.android.internal.os.ZygoteInit.readArgumentList()
* Presently the wire format to the zygote process is:
* a) a count of arguments (argc, in essence)
* b) a number of newline-separated argument strings equal to count
*
* After the zygote process reads these it will write the pid of
* the child or -1 on failure, followed by boolean to
* indicate whether a wrapper process was used.
*/
final BufferedWriter writer = zygoteState.writer;
final DataInputStream inputStream = zygoteState.inputStream;
writer.write(Integer.toString(args.size()));
writer.newLine();
int sz = args.size();
for (int i = 0; i < sz; i++) {
String arg = args.get(i);
if (arg.indexOf('\n') >= 0) {
throw new ZygoteStartFailedEx(
"embedded newlines not allowed");
}
writer.write(arg);
writer.newLine();
}
writer.flush();
// Should there be a timeout on this?
ProcessStartResult result = new ProcessStartResult();
result.pid = inputStream.readInt();
if (result.pid < 0) {
throw new ZygoteStartFailedEx("fork() failed");
}
result.usingWrapper = inputStream.readBoolean();
return result;
} catch (IOException ex) {
zygoteState.close();
throw new ZygoteStartFailedEx(ex);
}
}
又回到zygote那邊的socket處理了烟馅。最終通過反射調(diào)用到ActivityThread的Main函數(shù)：
public static void main(String[] args) {
SamplingProfilerIntegration.start();
// CloseGuard defaults to true and can be quite spammy. We
// disable it here, but selectively enable it later (via
// StrictMode) on debug builds, but using DropBox, not logs.
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
// Set the reporter for event logging in libcore
EventLogger.setReporter(new EventLoggingReporter());
Security.addProvider(new AndroidKeyStoreProvider());
// Make sure TrustedCertificateStore looks in the right place for CA certificates
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);
Process.setArgV0("<pre-initialized>");
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();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
這個(gè)函數(shù)在上一篇文章中介紹過说庭，本篇主要分析：
ActivityThread thread = new ActivityThread();
thread.attach(false);
創(chuàng)建ActivityThread實(shí)例后，attach又做了什么處理郑趁？
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
ViewRootImpl.addFirstDrawHandler(new Runnable() {
@Override
public void run() {
ensureJitEnabled();
}
});
android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
// Ignore
}
...
}
終于又和AMS關(guān)聯(lián)上了：
@Override
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
...
// See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
badApp = true;
}
}
...
}
又繞又繞...
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
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 (!isFrontStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked(null);
if (hr != null) {
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
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);
}
return didSomething;
}
終于繞回來了刊驴，通過這個(gè)進(jìn)程查找相關(guān)信息，然后取啟動(dòng)realStartActivityLocked：
final boolean realStartActivityLocked(ActivityRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig)
throws RemoteException {
...
ProfilerInfo profilerInfo = profileFile != null
? new ProfilerInfo(profileFile, profileFd, mService.mSamplingInterval,
mService.mAutoStopProfiler) : null;
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_TOP);
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
r.compat, r.task.voiceInteractor, app.repProcState, r.icicle, r.persistentState,
results, newIntents, !andResume, mService.isNextTransitionForward(),
profilerInfo);
...
}
終于看到使用ActivityThread去啟動(dòng)一個(gè)Activity了：
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, CompatibilityInfo compatInfo,
IVoiceInteractor voiceInteractor, int procState, Bundle state,
PersistableBundle persistentState, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward,
ProfilerInfo profilerInfo) {
updateProcessState(procState, false);
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
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;
updatePendingConfiguration(curConfig);
sendMessage(H.LAUNCH_ACTIVITY, r);
}
關(guān)于Handler我之前也寫過一篇文章寡润，是基于Handler實(shí)現(xiàn)原理作的分析捆憎，但是沒有涉及到Android Activity模塊，實(shí)際上Android系統(tǒng)事件(包括啟動(dòng)梭纹、繪制躲惰、事件收發(fā)處理)是由Handler消息。Activity的Looper雖然在loop()里面阻塞著变抽，但是Activity本身沒有阻塞础拨，就是因?yàn)槭录际峭ㄟ^Handler分發(fā)處理的氮块。關(guān)于這個(gè)自己可以查看資料且轨，我后續(xù)也會(huì)寫文章說明题翻。
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);
handleLaunchActivity(r, null);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
...
}
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;
if (r.profilerInfo != null) {
mProfiler.setProfiler(r.profilerInfo);
mProfiler.startProfiling();
}
// Make sure we are running with the most recent config.
handleConfigurationChanged(null, null);
if (localLOGV) Slog.v(
TAG, "Handling launch of " + r);
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed);
if (!r.activity.mFinished && r.startsNotResumed) {
try {
r.activity.mCalled = false;
mInstrumentation.callActivityOnPause(r.activity);
if (r.isPreHoneycomb()) {
r.state = oldState;
}
if (!r.activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onPause()");
}
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException(
"Unable to pause activity "
+ r.intent.getComponent().toShortString()
+ ": " + e.toString(), e);
}
}
r.paused = true;
}
} else {
// If there was an error, for any reason, tell the activity
// manager to stop us.
try {
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED, null, false);
} catch (RemoteException ex) {
// Ignore
}
}
}
周轉(zhuǎn)了這么多次唯绍，終于看到了啟動(dòng)Activity的實(shí)現(xiàn)代碼了：
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
//獲取Activity對(duì)象
Activity activity = null;
try {
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 (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) {
//創(chuàng)建Context上下文
Context appContext = createBaseContextForActivity(r, activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mCompatConfiguration);
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
+ r.activityInfo.name + " with config " + config);
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.voiceInteractor);
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;
//回調(diào)Activity的OnCreate
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) {
//回調(diào)Activity的OnStart
activity.performStart();
r.stopped = false;
}
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state != null || r.persistentState != null) {
//回調(diào)Activity的OnRestoreInstanceState
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
r.persistentState);
}
} else if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
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;
}
這是個(gè)關(guān)鍵函數(shù)黎做，從這個(gè)函數(shù)中可以看到Activity的創(chuàng)建害捕、OnCreate茶凳、以及OnRestoreInstanceState和OnPostCreate的調(diào)用匿辩。
首先來看Activity的創(chuàng)建：
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
Instrumentation又出現(xiàn)了阳准，創(chuàng)建Activity如下芳悲，它利用了反射機(jī)制：
public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return (Activity)cl.loadClass(className).newInstance();
}
Activity創(chuàng)建完后立肘，用這個(gè)創(chuàng)建出來的Activity初始化了一個(gè)Context，重要的是調(diào)用了attach方法：
final void attach(Context context, ActivityThread aThread,
Instrumentation instr, IBinder token, int ident,
Application application, Intent intent, ActivityInfo info,
CharSequence title, Activity parent, String id,
NonConfigurationInstances lastNonConfigurationInstances,
Configuration config, IVoiceInteractor voiceInteractor) {
attachBaseContext(context);
mFragments.attachActivity(this, mContainer, null);
mWindow = PolicyManager.makeNewWindow(this);
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
mWindow.setSoftInputMode(info.softInputMode);
}
if (info.uiOptions != 0) {
mWindow.setUiOptions(info.uiOptions);
}
mUiThread = Thread.currentThread();
mMainThread = aThread;
mInstrumentation = instr;
mToken = token;
mIdent = ident;
mApplication = application;
mIntent = intent;
mComponent = intent.getComponent();
mActivityInfo = info;
mTitle = title;
mParent = parent;
mEmbeddedID = id;
mLastNonConfigurationInstances = lastNonConfigurationInstances;
if (voiceInteractor != null) {
if (lastNonConfigurationInstances != null) {
mVoiceInteractor = lastNonConfigurationInstances.voiceInteractor;
} else {
mVoiceInteractor = new VoiceInteractor(voiceInteractor, this, this,
Looper.myLooper());
}
}
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
if (mParent != null) {
mWindow.setContainer(mParent.getWindow());
}
mWindowManager = mWindow.getWindowManager();
mCurrentConfig = config;
}
從attach函數(shù)中有幾個(gè)關(guān)鍵函數(shù)需要注意:
mWindow = PolicyManager.makeNewWindow(this);
mWindow.setCallback(this);
mWindow.setWindowManager(
(WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
mToken, mComponent.flattenToString(),
(info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
mWindowManager = mWindow.getWindowManager();
這里創(chuàng)建了和Window的關(guān)聯(lián)名扛，一個(gè)Activity就有一個(gè)Window谅年，關(guān)于和Window的關(guān)聯(lián)會(huì)在另一篇文章中說明。
繼續(xù)往下分析就看到了終于想要看到的OnCreat肮韧、OnStart相關(guān)函數(shù)：
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
activity.performStart();
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state, r.persistentState);
以Instrumentation中callActivityOnCreate為例說明：
public void callActivityOnCreate(Activity activity, Bundle icicle,
PersistableBundle persistentState) {
prePerformCreate(activity);
activity.performCreate(icicle, persistentState);
postPerformCreate(activity);
}
會(huì)在其中調(diào)用到Activity中的performCreate函數(shù)：
final void performCreate(Bundle icicle, PersistableBundle persistentState) {
onCreate(icicle, persistentState);
mActivityTransitionState.readState(icicle);
performCreateCommon();
}
在Activity中的performCreate函數(shù)里調(diào)用了onCreate融蹂。開發(fā)人員寫一個(gè)應(yīng)用時(shí)入口Activity都是繼承于Activity的，而且要重寫OnCreat方法弄企，根據(jù)Java的多態(tài)特性超燃，這里就會(huì)調(diào)用到子類的OnCreat處理，所以這里就是為什么我們?cè)谧约旱膽?yīng)用中能有類似OnCreat拘领、OnStart意乓、OnResume、OnPause约素、OnStop届良、OnDestroy等生命周期的說法。
雖然在OnStart的實(shí)現(xiàn)和OnCreat調(diào)用不一樣圣猎，但是把源碼展開來看實(shí)際上是一樣的：
final void performStart() {
mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());
mFragments.noteStateNotSaved();
mCalled = false;
mFragments.execPendingActions();
mInstrumentation.callActivityOnStart(this);
if (!mCalled) {
throw new SuperNotCalledException(
"Activity " + mComponent.toShortString() +
" did not call through to super.onStart()");
}
mFragments.dispatchStart();
if (mAllLoaderManagers != null) {
final int N = mAllLoaderManagers.size();
LoaderManagerImpl loaders[] = new LoaderManagerImpl[N];
for (int i=N-1; i>=0; i--) {
loaders[i] = mAllLoaderManagers.valueAt(i);
}
for (int i=0; i<N; i++) {
LoaderManagerImpl lm = loaders[i];
lm.finishRetain();
lm.doReportStart();
}
}
mActivityTransitionState.enterReady(this);
}
然后在內(nèi)部調(diào)用了：
mInstrumentation.callActivityOnStart(this);
public void callActivityOnStart(Activity activity) {
activity.onStart();
}
對(duì)吧士葫，實(shí)際上和OnCreat的方式是一樣的。
本篇文章以應(yīng)用調(diào)用StartActivity為入口送悔，分析了在Android Framework中是如何實(shí)現(xiàn)Activity生命周期慢显，其中在分析過程中有很多和Window，堆棧相關(guān)的處理放祟，本篇文章只是簡單分析鳍怨，之后有更深入的分析時(shí)再更新或者寫另外寫一篇文章。
