从Laucher中启动Activity的流程
完整流程图
sequenceDiagram
autonumber
Actor User
box User Process
participant Laucher
participant Activity
participant Instrument
participant ActivityManagerProxy
end
box ActivityManagerService
participant ActivityManagerService
participant ActivityStack
participant ApplicationThreadProxy
end
box User Process
participant ApplicationThread
participant ActivityThread
participant H
end
rect rgb(191, 223, 255)
note right of User: try to start Specified Activity
User->>+ Laucher: startActivitySafely
Laucher->>+ Activity: startActivity
Activity->>Activity: startActivityForResult
Activity->>+Instrument: execStartActivity
Instrument->>+ActivityManagerProxy: startActivity
ActivityManagerProxy->>+ActivityManagerService: startActivity
ActivityManagerService->>+ActivityStack: startActivityMayWait
ActivityStack->>ActivityStack: startActivityLocked
ActivityStack->>ActivityStack:startActivityUncheckedLocked
ActivityStack->>ActivityStack: startActivityLocked
ActivityStack->>ActivityStack: resumeTopActivityLocked
end
rect rgb(200, 150, 255)
note right of Instrument: pause Launcher
ActivityStack->>ActivityStack: startPausingLocked
ActivityStack->>+ApplicationThreadProxy: schedulePauseActivity
deactivate ActivityStack
ApplicationThreadProxy->>+ApplicationThread: schedulePauseActivity
ApplicationThread->>+ActivityThread: queryOrSendMessage
ActivityThread->>+ H: handleMessage
H->>-ActivityThread: handlePauseActivity
ActivityThread->>Laucher:onUserLeavingHint
ActivityThread->>Laucher:onPause
deactivate Laucher
deactivate Activity
ActivityThread->>ActivityThread:QueuedWork.waitToFinish
ActivityThread->>-ActivityManagerProxy:activityPaused
ActivityManagerProxy->>ActivityManagerService:activityPaused
ActivityManagerService->>+ActivityStack: activityPaused
end
rect rgb(191, 223, 255)
note right of Instrument: resume Specified Activity
ActivityStack->>ActivityStack:completePauseLocked
ActivityStack->>ActivityStack:resumeTopActivityLocked
ActivityStack->>ActivityStack:startSepcificActivityLocked
ActivityStack->>+ActivityManagerService:startProcessLocked
deactivate ActivityStack
ActivityManagerService->>ActivityManagerService:startProcessLocked
ActivityManagerService->>+ActivityThread:main
ActivityThread->>ActivityManagerProxy:attachApplication
ActivityManagerProxy->>ActivityManagerService:attachApplication
ActivityManagerService->>ActivityManagerService:attachApplicationLocked
ActivityManagerService->>ActivityStack:realStartActivityLocked
deactivate ActivityManagerService
ActivityStack->>ApplicationThreadProxy:scheduleLaunchActivity
ApplicationThreadProxy->>ApplicationThread:scheduleLaunchActivity
ApplicationThread->>ActivityThread:queueOrSendMessage
ActivityThread->>H:handleMessage
H->>+ActivityThread:handleLaunchActivity
ActivityThread->>ActivityThread:performLaunchActivity
ActivityThread->>Activity: attach
ActivityThread->>Activity:onCreate
ActivityThread->>ActivityThread:Looper.loop
deactivate ActivityThread
end
详细步骤
step 1 执行Laucher的startActivitySafely方法，该方法调用了Activity的startActivity方法
step 2 执行Activity的startActivity方法：
public void startActivity(Intent intent, @Nullable Bundle options) {
...
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
startActivityForResult(intent, -1);
}
}
，该方法调用了Activity的startActivityForResult方法
step 3 执行startActivityForResult方法，Laucher不存在mParent，于是，执行下述语句
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options) {
if (mParent == null) {
...
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
...
} else {
...
}
}
，Activity的mInstrumentation成员为Instrumentation类的一个对象，用于和Activity交互和监控Activity，这里调用了其execStartActivity方法
step 4 执行execStartActivity方法：
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;
...
try {
...
int result = ActivityTaskManager.getDefault().startActivity(whoThread,
who.getOpPackageName(), who.getAttributionTag(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()), token,
target != null ? target.mEmbeddedID : null, requestCode, 0, null, options);
notifyStartActivityResult(result, options);
checkStartActivityResult(result, intent);
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
return null;
}
，方法通过ActivityManager.getService()方法获取到了ActivityMangerProxy的对象，
/**
* class: ActivityTaskManager
**/
public static IActivityTaskManager getService() {
return IActivityTaskManagerSingleton.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;
}
};
可以看出，返回了一个单例，实现了IActivityManager这个接口，用于与ActivityManagerService进行交互，并调用startActivity方法
step 5 执行startActivity方法：
@Override public int startActivity(android.app.IApplicationThread caller, java.lang.String callingPackage, android.content.Intent intent, java.lang.String resolvedType, android.os.IBinder resultTo, java.lang.String resultWho, int requestCode, int flags, android.app.ProfilerInfo profilerInfo, android.os.Bundle options) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain(asBinder());
android.os.Parcel _reply = android.os.Parcel.obtain();
int _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeStrongInterface(caller);
_data.writeString(callingPackage);
_data.writeTypedObject(intent, 0);
_data.writeString(resolvedType);
_data.writeStrongBinder(resultTo);
_data.writeString(resultWho);
_data.writeInt(requestCode);
_data.writeInt(flags);
_data.writeTypedObject(profilerInfo, 0);
_data.writeTypedObject(options, 0);
boolean _status = mRemote.transact(Stub.TRANSACTION_startActivity, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
，方法包装了一个Parcel并通过Binder发送给了IActivity$Stub，其code为Stub.TRANSACTION_startActivity,IActivity$Stub判断code的类型为Stub.TRANSACTION_startActivity，并执行：
public boolean onTransact(){
...
switch (code)
{
...
case TRANSACTION_startActivity:
{
android.app.IApplicationThread _arg0;
_arg0 = android.app.IApplicationThread.Stub.asInterface(data.readStrongBinder());
java.lang.String _arg1;
_arg1 = data.readString();
android.content.Intent _arg2;
_arg2 = data.readTypedObject(android.content.Intent.CREATOR);
java.lang.String _arg3;
_arg3 = data.readString();
android.os.IBinder _arg4;
_arg4 = data.readStrongBinder();
java.lang.String _arg5;
_arg5 = data.readString();
int _arg6;
_arg6 = data.readInt();
int _arg7;
_arg7 = data.readInt();
android.app.ProfilerInfo _arg8;
_arg8 = data.readTypedObject(android.app.ProfilerInfo.CREATOR);
android.os.Bundle _arg9;
_arg9 = data.readTypedObject(android.os.Bundle.CREATOR);
data.enforceNoDataAvail();
int _result = this.startActivity(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5, _arg6, _arg7, _arg8, _arg9);
reply.writeNoException();
reply.writeInt(_result);
break;
}
...
}
...
}
，方法调用了Stub的startActivity方法，该方法由ActivityManagerService重写ActivityManagerNative实现
public final class ActivityManagerService extends ActivityManagerNative
step 6 调用ActivityManagerService的startActivity方法：
public final int startActivity(IApplicationThread caller,
Intent intent, String resolvedType, Uri[] grantedUriPermissions,
int grantedMode, IBinder resultTo,
String resultWho, int requestCode, boolean onlyIfNeeded,
boolean debug) {
return mMainStack.startActivityMayWait(caller, intent, resolvedType,
grantedUriPermissions, grantedMode, resultTo, resultWho,
requestCode, onlyIfNeeded, debug, null, null);
}
，方法调用了mMainStack的startActivityMayWait方法。mMainStack是ActivityStack的实例，负责管理应用程序的Activity和任务栈
step 7 执行ActivityStack.startActivityMayWait方法:
final int startActivityMayWait(IApplicationThread caller,
Intent intent, String resolvedType, Uri[] grantedUriPermissions,
int grantedMode, IBinder resultTo,
String resultWho, int requestCode, boolean onlyIfNeeded,
boolean debug, WaitResult outResult, Configuration config) {
// Refuse possible leaked file descriptors
...
// Collect information about the target of the Intent.
...
synchronized (mService) {
...
int res = startActivityLocked(caller, intent, resolvedType,
grantedUriPermissions, grantedMode, aInfo,
resultTo, resultWho, requestCode, callingPid, callingUid,
onlyIfNeeded, componentSpecified);
...
}
}
，调用了startActivityLocked方法
step 8 执行startActivityLocked方法：
final int startActivityLocked(IApplicationThread caller,
Intent intent, String resolvedType,
Uri[] grantedUriPermissions,
int grantedMode, ActivityInfo aInfo, IBinder resultTo,
String resultWho, int requestCode,
int callingPid, int callingUid, boolean onlyIfNeeded,
boolean componentSpecified) {
int err = START_SUCCESS;
ProcessRecord callerApp = null;
...
ActivityRecord sourceRecord = null;
ActivityRecord resultRecord = null;
...
ActivityRecord r = new ActivityRecord(mService, this, callerApp, callingUid,
intent, resolvedType, aInfo, mService.mConfiguration,
resultRecord, resultWho, requestCode, componentSpecified);
...
return startActivityUncheckedLocked(r, sourceRecord,
grantedUriPermissions, grantedMode, onlyIfNeeded, true);
}
方法给要创建的Activity创建了一个ActivityRecord，并设置其sourceRecord为Launcher，以此调用startActivityUncheckedLocked方法
step 9 执行startActivityUnchekedLocked方法：
final int startActivityUncheckedLocked(ActivityRecord r,
ActivityRecord sourceRecord, Uri[] grantedUriPermissions,
int grantedMode, boolean onlyIfNeeded, boolean doResume) {
...
boolean addingToTask = false;
...
boolean newTask = false;
if (r.resultTo == null && !addingToTask
&& (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
mService.mCurTask++;
if (mService.mCurTask <= 0) {
mService.mCurTask = 1;
}
...
newTask = true;
if (mMainStack) {
mService.addRecentTaskLocked(r.task);
}
}
...
startActivityLocked(r, newTask, doResume);
return START_SUCCESS;
}
对于要启动的Activity而言，newTask == true，然后调用重载的startActivityLocked方法
step 10 执行startActivityLocked方法：
private final void startActivityLocked(ActivityRecord r, boolean newTask,
boolean doResume) {
final int NH = mHistory.size();
int addPos = -1;
...
if (addPos < 0) {
addPos = NH;
}
...
mHistory.add(addPos, r);
...
if (doResume) {
resumeTopActivityLocked(null);
}
}
，由于启动新Activity且newTask == true，于是将其ActivityRecord插入到栈的顶部，并执行resumeTopActivityLocked方法
step 11 执行resumeTopActivityLocked方法：
final boolean resumeTopActivityLocked(ActivityRecord prev) {
...
final boolean userLeaving = mUserLeaving;
mUserLeaving = false;
...
// If the top activity is the resumed one, nothing to do.
if (mResumedActivity == next && next.state == ActivityState.RESUMED) {
...
return false;
}
// If we are sleeping, and there is no resumed activity, and the top
// activity is paused, well that is the state we want.
if ((mService.mSleeping || mService.mShuttingDown)
&& mLastPausedActivity == next && next.state == ActivityState.PAUSED) {
...
return false;
}
...
// If we are currently pausing an activity, then don't do anything
// until that is done.
if (mPausingActivity != null) {
...
return false;
}
// We need to start pausing the current activity so the top one
// can be resumed...
if (mResumedActivity != null) {
startPausingLocked(userLeaving, false);
return true;
}
...
}
，在方法中，判断当前的Activity是否resumed、是否正在休眠、是否正在停止一个Activity，如果都不是，则调用startPausingLocked方法停止正在运行的进程
step 12 执行startPausingLocked方法：
private final void startPausingLocked(boolean userLeaving, boolean uiSleeping) {
ActivityRecord prev = mResumedActivity;
...
mResumedActivity = null;
mPausingActivity = prev;
...
mLastPausedActivity = prev;
if (prev.app != null && prev.app.thread != null) {
try {
...
prev.app.thread.schedulePauseActivity(prev, prev.finishing, userLeaving,
prev.configChangeFlags);
...
} catch (Exception e) {
...
}
}
...
}
，调用了prev.app.thread.schedulePauseActivity方法，prev.app.thead为一个ApplicationThread$ApplicationThreadProxy类型的对象
step 13 执行schedulePauseActivity方法：
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges) throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
data.writeStrongBinder(token);
data.writeInt(finished ? 1 : 0);
data.writeInt(userLeaving ? 1 :0);
data.writeInt(configChanges);
mRemote.transact(SCHEDULE_PAUSE_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
，方法向远程服务发送了一个SCHEDULE_PAUSE_ACTIVITY_TRANSACTION的code，远程服务为ApplicationThreadNative类型的Stub，并实现了IApplicationThread接口：
public abstract class ApplicationThreadNative extends Binder implements IApplicationThread
，当Stub接受到了请求后，执行onTransact方法：
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
case SCHEDULE_PAUSE_ACTIVITY_TRANSACTION:
{
data.enforceInterface(IApplicationThread.descriptor);
IBinder b = data.readStrongBinder();
boolean finished = data.readInt() != 0;
boolean userLeaving = data.readInt() != 0;
int configChanges = data.readInt();
schedulePauseActivity(b, finished, userLeaving, configChanges);
return true;
}
}
}
，调用了schedulePauseActivity方法
step 14 执行schedulePauseActivity方法：
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges) {
queueOrSendMessage(
finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
token,
(userLeaving ? 1 : 0),
configChanges);
}
，该方法由ActivityThread$ApplicationThread中实现，调用queueOrSendMessage方法发送PAUSE_ACTIVITY的请求
step 15 执行queueOrSendMessage方法：
...
final H mH = new H();
...
private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) {
synchronized (this) {
if (DEBUG_MESSAGES) Slog.v(
TAG, "SCHEDULE " + what + " " + mH.codeToString(what)
+ ": " + arg1 + " / " + obj);
Message msg = Message.obtain();
msg.what = what;
msg.obj = obj;
msg.arg1 = arg1;
msg.arg2 = arg2;
mH.sendMessage(msg);
}
}
，向Handler发送了一条PAUSE_ACTIVITY的消息
step 16 执行sendMessage方法向mH发送一条消息，mH接收到消息后执行handleMessage方法:
public void handleMessage(Message msg) {
...
switch (msg.what) {
case PAUSE_ACTIVITY:
handlePauseActivity((IBinder)msg.obj, false, msg.arg1 != 0, msg.arg2);
maybeSnapshot();
break;
...
}
...
}
，调用了ActivityThread的handlePauseActivity方法，Activity$H继承了Handler类：
private final class H extends Handler
step 17 执行handlePauseActivity方法：
private final void handlePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges) {
ActivityClientRecord r = mActivities.get(token);
if (r != null) {
if (userLeaving) {
performUserLeavingActivity(r);
}
Bundle state = performPauseActivity(token, finished, true);
QueuedWork.waitToFinish();
// Tell the activity manager we have paused.
try {
ActivityManagerNative.getDefault().activityPaused(token, state);
} catch (RemoteException ex) {
}
}
}
，首先，调用performUserLeavingActivity方法，向Launcher发送userLeaving
step 18 执行performUserLeavingActivity方法：
final void performUserLeavingActivity(ActivityClientRecord r) {
mInstrumentation.callActivityOnUserLeaving(r.activity);
}
，方法通过Instrumentation向Laucher发送userLeaving，执行：
/**
* class: Instrumentation
**/
public void callActivityOnUserLeaving(Activity activity) {
activity.performUserLeaving();
}
step 19 执行完performUserLeavingActivity后，执行performPauseActivity方法：
final Bundle performPauseActivity(IBinder token, boolean finished,
boolean saveState) {
ActivityClientRecord r = mActivities.get(token);
return r != null ? performPauseActivity(r, finished, saveState) : null;
}
final Bundle performPauseActivity(ActivityClientRecord r, boolean finished,
boolean saveState) {
...
try {
...
r.activity.mCalled = false;
mInstrumentation.callActivityOnPause(r.activity);
...
}
...
r.paused = true;
return state;
}
，该方法设置Launcher的r.mCalled = false，并调用了Instrumentation.callActivityOnPause方法，然后设置r.paused = true
public void callActivityOnPause(Activity activity) {
activity.performPause();
}
step 20 执行QueuedWork.waitToFinish方法：
/**
* Is called from the Activity base class's onPause(), after
* BroadcastReceiver's onReceive, after Service command handling,
**/
public static void waitToFinish() {
Runnable toFinish;
while ((toFinish = sPendingWorkFinishers.poll()) != null) {
toFinish.run();
}
}
，等待前面的任务完成执行
step 21 在 step 17中，通过ActivityManagerNative.getDefault()获取到了ActivityManagerProxy对象，并调用其activityPaused方法向ActivityManagerService通知top Activity已经被pause了：
public void activityPaused(IBinder token, Bundle state) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(token);
data.writeBundle(state);
mRemote.transact(ACTIVITY_PAUSED_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
，方法发送一个code为ACTIVITY_PAUSED_TRANSACTION的Parcel
step 22 收到通信后，ActivityManagerService通过:
public boolean onTransact(){
...
switch (code)
{
case ACTIVITY_PAUSED_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
IBinder token = data.readStrongBinder();
Bundle map = data.readBundle();
activityPaused(token, map);
reply.writeNoException();
return true;
}
}
...
}
调用activityPaused方法：
public final void activityPaused(IBinder token, Bundle icicle) {
...
mMainStack.activityPaused(token, icicle, false);
...
}
,方法调用ActivityStack的activityPaused方法
step 23 执行ActivityStack.activityPaused方法：
final void activityPaused(IBinder token, Bundle icicle, boolean timeout) {
...
ActivityRecord r = null;
synchronized (mService) {
int index = indexOfTokenLocked(token);
if (index >= 0) {
r = (ActivityRecord)mHistory.get(index);
...
mHandler.removeMessages(PAUSE_TIMEOUT_MSG, r);
if (mPausingActivity == r) {
r.state = ActivityState.PAUSED;
completePauseLocked();
}
...
}
}
}
，找到Laucher对应的ActivityRecord，在step 12中，语句mPausingActivity = prev设置了mPausingActivity为Launcher，于是，设置Launcher的ActivityRecord.state为PAUSED，并调用completePauseLocked方法
step 24 执行completePauseLocked方法：
private final void completePauseLocked() {
ActivityRecord prev = mPausingActivity;
if (prev != null) {
...
mPausingActivity = null;
}
if (!mService.mSleeping && !mService.mShuttingDown) {
resumeTopActivityLocked(prev);
}
...
}
，将mPausingActivity设置为null并再次调用resumeTopActivityLocked方法
step 25 执行resumeTopActivityLocked方法：
final boolean resumeTopActivityLocked(ActivityRecord prev) {
...
if (next.app != null && next.app.thread != null){
...
}
else {
...
startSpecificActivityLocked(next, true, true);
}
return true;
}
，此时，mResumedActivity == null， 于是调用startSpecificActivityLocked方法
step 26 执行startSpecificActivityLocked方法：
private final void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid);
...
if (app != null && app.thread != null) {
...
}
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false);
}
，此时，由于app == null && app.thread == null，于是继续执行mService.startProcessLocked方法，其中mService指向ActivityManagerService
step 27 ActivityManagerService执行startProcessLocked方法：
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting) {
ProcessRecord app = getProcessRecordLocked(processName, info.uid);
...
if (app == null) {
app = newProcessRecordLocked(null, info, processName);
mProcessNames.put(processName, info.uid, app);
}
...
startProcessLocked(app, hostingType, hostingNameStr);
return (app.pid != 0) ? app : null;
}
，创建一个ProcessRecord，并调用startProcessLocked方法运行该Process
step 28
private final void startProcessLocked(ProcessRecord app,
String hostingType, String hostingNameStr) {
...
try {
...
int pid = Process.start("android.app.ActivityThread",
mSimpleProcessManagement ? app.processName : null, uid, uid,
gids, debugFlags, null);
...
}
...
}
，查看Process.start方法：
public static final int start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int debugFlags,
String[] zygoteArgs)
{
...
else {
...
Runnable runnable = new Runnable() {
public void run() {
Process.invokeStaticMain(processClass);
}
};
if (niceName != null) {
new Thread(runnable, niceName).start();
} else {
new Thread(runnable).start();
}
return 0;
}
}
，可以看到，其创建了一个线程，并运行invokeStaticMain方法：
private static void invokeStaticMain(String className) {
Class cl;
Object args[] = new Object[1];
args[0] = new String[0]; //this is argv
try {
cl = Class.forName(className);
cl.getMethod("main", new Class[] { String[].class })
.invoke(null, args);
}
...
}
，由于之前传入的processClass为"android.app.ActivityThread"，于是在此通过反向代理调用其静态main方法
step 29 执行main方法：
public static final void main(String[] args) {
...
ActivityThread thread = new ActivityThread();
thread.attach(false);
...
Looper.loop();
...
}
，可以看到，创建了一个ActivityThread的实例，并调用了attach方法：
private final void attach(boolean system) {
sThreadLocal.set(this);
mSystemThread = system;
if (!system) {
...
IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
...
}
}
...
}
，方法调用了ActivityManagerProxy的attachApplication方法，其中final ApplicationThread mAppThread = new ApplicationThread();在创建ActivityThread时创建
step 30 执行attachApplication方法，向ActivityManagerService发送ATTACH_APPLICATION_TRANSACTION请求：
public void attachApplication(IApplicationThread app) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
step 31 ActivityManagerService执行onTransact方法：
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
...
case ATTACH_APPLICATION_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
IApplicationThread app = ApplicationThreadNative.asInterface(
data.readStrongBinder());
if (app != null) {
attachApplication(app);
}
reply.writeNoException();
return true;
}
...
}
...
}
，调用attachApplication方法：
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
...
attachApplicationLocked(thread, callingPid);
...
}
}
，调用attachApplicationLocked方法
step 32 执行attachApplicationLocked方法：
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
// Find the application record that is being attached
ProcessRecord app;
...
app.thread = thread;
...
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
...
ActivityRecord hr = mMainStack.topRunningActivityLocked(null);
if (hr != null && normalMode) {
if (hr.app == null && app.info.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
if (mMainStack.realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (Exception e) {
...
}
} else {
...
}
}
}
，从Handler中移除PROC_START_TIMEOUT_MSG，并检查是否有Activity需要启动，于是调用ActivityStack.realStartActivityLocked方法
step 33 执行realStartActivityLocked方法：
final boolean realStartActivityLocked(ActivityRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig)
throws RemoteException {
...
try {
...
app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
System.identityHashCode(r),
r.info, r.icicle, results, newIntents, !andResume,
mService.isNextTransitionForward());
}
...
return true;
}
，调用了ApplicationThreadProxy的scheduleLaunchActivity方法
step 34 执行scheduleLaunchActivity方法：
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward)
throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
intent.writeToParcel(data, 0);
data.writeStrongBinder(token);
data.writeInt(ident);
info.writeToParcel(data, 0);
data.writeBundle(state);
data.writeTypedList(pendingResults);
data.writeTypedList(pendingNewIntents);
data.writeInt(notResumed ? 1 : 0);
data.writeInt(isForward ? 1 : 0);
mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
，向ApplicationThread发送一个SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION类型的请求
step 35 ApplicationThread执行onTransact方法：
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch(code){
case SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION:
{
data.enforceInterface(IApplicationThread.descriptor);
Intent intent = Intent.CREATOR.createFromParcel(data);
IBinder b = data.readStrongBinder();
int ident = data.readInt();
ActivityInfo info = ActivityInfo.CREATOR.createFromParcel(data);
Bundle state = data.readBundle();
List<ResultInfo> ri = data.createTypedArrayList(ResultInfo.CREATOR);
List<Intent> pi = data.createTypedArrayList(Intent.CREATOR);
boolean notResumed = data.readInt() != 0;
boolean isForward = data.readInt() != 0;
scheduleLaunchActivity(intent, b, ident, info, state, ri, pi,
notResumed, isForward);
return true;
}
}
}
，调用scheduleLaunchActivity方法:
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
，创建一个ActivityClientRecord，并调用queueOrSendMessage方法，向Handler发送LAUNCH_ACTIVITY信息
step 36 执行queueOrSendMessage方法，向ActivityThread发送LAUNCH_ACTIVITY类型的信息
step 37 执行queueOrSendMessage方法，向mH发送LAUNCH_ACTIVITY类型的信息
step 38 mH接受到消息后，通过handleMessage执行代码：
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + msg.what);
switch (msg.what) {
case LAUNCH_ACTIVITY: {
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo);
handleLaunchActivity(r, null);
} break;
}
}
，调用ActivityThread.handleLaunchActivity方法：
private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
...
handleResumeActivity(r.token, false, r.isForward);
...
} else {
...
}
}
，方法首先调用了performLaunchActivity方法
step 39 执行performLaunchActivity方法：
private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
r.intent.setExtrasClassLoader(cl);
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
...
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
...
if (activity != null) {
...
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstance,
r.lastNonConfigurationChildInstances, config);
...
mInstrumentation.callActivityOnCreate(activity, r.state);
...
r.activity = activity;
r.stopped = true;
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
...
}
r.paused = true;
mActivities.put(r.token, r);
}
...
return activity;
}
，首先，通过反射创建了一个Activity的实例，调用其attach到application中
step 40 执行attach方法：
final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token,
Application application, Intent intent, ActivityInfo info, CharSequence title,
Activity parent, String id, Object lastNonConfigurationInstance,
Configuration config) {
attach(context, aThread, instr, token, 0, application, intent, info, title, parent, id,
lastNonConfigurationInstance, null, config);
}
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,
Object lastNonConfigurationInstance,
HashMap<String,Object> lastNonConfigurationChildInstances,
Configuration config) {
attachBaseContext(context);
//activity信息设置
...
}
step 41 完成attach后，通过调用Instrumentation.callActivityOnCreate方法：
public void callActivityOnCreate(Activity activity, Bundle icicle) {
...
activity.onCreate(icicle);
...
}
，调用了Activity的onCreate方法，至此，完成了Activity的启动
step 42 在step 29中，执行了main方法中的attach方法，在attach执行完后，执行 Looper.loop()
从Activity中启动同一进程中的另一Activity
基本与从Laucher中启动Activity的流程相同， 不同的是：
- 在 step 9 中，由于Activity指定的进程为存在，于是
newTask == false并设置r.task = sourceRecord.task - 在 step 10 中，在
Activity Stack中从上至下搜索一个与当前Activity同进程的Activity的位置i，并设置插入位置addPos=i+1 - 在 step 26 中，由于Activity所在的进程已经启动，于是
app != null && app.thread != null的结果为true，于是执行该选择语句下的realStartActivityLocked
从Activity中启动另一进程中的另一Activity
与从Laucher中启动Activity的过程一致