该方法调用了ActivityManager.getService().activityStopped(mActivity.token, mState, mPersistentState, mDescription)方法。还将2.1中创建的mState当参数传进来了。

2.4 ActivityManagerService.activityStopped()

//ActivityManagerService.java
@Override
public final void activityStopped(IBinder token, Bundle icicle,
        PersistableBundle persistentState, CharSequence description) {
    if (DEBUG_ALL) Slog.v(TAG, "Activity stopped: token=" + token);

    // Refuse possible leaked file descriptors
    if (icicle != null && icicle.hasFileDescriptors()) {
        throw new IllegalArgumentException("File descriptors passed in Bundle");
    }

    final long origId = Binder.clearCallingIdentity();

    synchronized (this) {
        final ActivityRecord r = ActivityRecord.isInStackLocked(token);
        if (r != null) {
            r.activityStoppedLocked(icicle, persistentState, description);
        }
    }

    trimApplications();

    Binder.restoreCallingIdentity(origId);
}

重点关注r.activityStoppedLocked(icicle, persistentState, description)

2.5 ActivityRecord.activityStoppedLocked

final void activityStoppedLocked(Bundle newIcicle, PersistableBundle newPersistentState,
        CharSequence description) {
    final ActivityStack stack = getStack();
    if (mState != STOPPING) {
        Slog.i(TAG, "Activity reported stop, but no longer stopping: " + this);
        stack.mHandler.removeMessages(STOP_TIMEOUT_MSG, this);
        return;
    }
    if (newPersistentState != null) {
        persistentState = newPersistentState;
        service.notifyTaskPersisterLocked(task, false);
    }
    if (DEBUG_SAVED_STATE) Slog.i(TAG_SAVED_STATE, "Saving icicle of " + this + ": " + icicle);

    if (newIcicle != null) {
        icicle = newIcicle;
        haveState = true;
        launchCount = 0;
        updateTaskDescription(description);
    }
    if (!stopped) {
        if (DEBUG_STATES) Slog.v(TAG_STATES, "Moving to STOPPED: " + this + " (stop complete)");
        stack.mHandler.removeMessages(STOP_TIMEOUT_MSG, this);
        stopped = true;
        setState(STOPPED, "activityStoppedLocked");

        mWindowContainerController.notifyAppStopped();

        if (finishing) {
            clearOptionsLocked();
        } else {
            if (deferRelaunchUntilPaused) {
                stack.destroyActivityLocked(this, true /* removeFromApp */, "stop-config");
                mStackSupervisor.resumeFocusedStackTopActivityLocked();
            } else {
                mStackSupervisor.updatePreviousProcessLocked(this);
            }
        }
    }
}

我们注意到最终bundle数据会保存在ActivityRecord的icicle对象中。

总结：onSaveInstanceState方法是当Activity调用了onStop后，会调用到ActivityThread的callActivityOnSaveInstanceState()方法，把Activity需要保存的数据放入Bundle对象中，并且随后通过IPC进程间通信机制，调用ActivityManagerService的activityStopped方法，将Bundle对象保存到AMS端的ActivityRecord中。

2.6 被杀端后恢复数据过程

2.7 ActivityStackSupervisor.realStartActivityLocked

//ActivityStackSupervisor.java
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
          boolean andResume, boolean checkConfig) throws RemoteException {
     // 忽略其它代码
     // Create activity launch transaction.
      final ClientTransaction clientTransaction = ClientTransaction.obtain(app.thread,
              r.appToken);
      clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
              System.identityHashCode(r), r.info,
              // TODO: Have this take the merged configuration instead of separate global
              // and override configs.
              mergedConfiguration.getGlobalConfiguration(),
              mergedConfiguration.getOverrideConfiguration(), r.compat,
              r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
              r.persistentState, results, newIntents, mService.isNextTransitionForward(),
              profilerInfo));
    // 忽略其它代码
}

我们看到最终是通过ActivityRecord.icicle恢复数据。

2.8 LaunchActivityItem.execute()

//LaunchActivityItem.java
@Override
public void execute(ClientTransactionHandler client, IBinder token,
        PendingTransactionActions pendingActions) {
    Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
    ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,
            mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,
            mPendingResults, mPendingNewIntents, mIsForward,
            mProfilerInfo, client);
    client.handleLaunchActivity(r, pendingActions, null /* customIntent */);
    Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}

2.9 ActivityThread.performLaunchActivity(ActivityClientRecord r, Intent customIntent)

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent){
   activity.mCalled = false;
    if (r.isPersistable()) {
        mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
    } else {
        mInstrumentation.callActivityOnCreate(activity, r.state);
    }
}

3. onRetainNonConfigurationInstance()

该方法是在重建Activity时调用performDestoryActivity时会保存数据。

ActivityClientRecord performDestroyActivity(IBinder token, boolean finishing,
          int configChanges, boolean getNonConfigInstance, String reason) {
  ActivityClientRecord r = mActivities.get(token);
  //省略一些代码
      if (getNonConfigInstance) {
          try {
              r.lastNOnConfigurationInstances= r.activity.retainNonConfigurationInstances();
          } catch (Exception e) {
              if (!mInstrumentation.onException(r.activity, e)) {
                  throw new RuntimeException(
                          "Unable to retain activity "
                          + r.intent.getComponent().toShortString()
                          + ": " + e.toString(), e);
        }
      }
  }

我们可以看到onRetainNonConfigurationInstance方法返回的Object会赋值给ActivityClientRecord的lastNonConfigurationInstances。

4. 答案

1. 颗粒度不一样。onSaveInstanceState()是保存到Bundle中，只能保存Bundle能接受的数据类型，比如一些基本类型的数据。而onRetainNonConfigurationInstance() 可以保存任何类型的数据，数据类型是Object

2. onSaveInstanceState()数据最终存储到ActivityManagerService的ActivityRecord中了，也就是存到系统进程中去了。而onRetainNonConfigurationInstance() 数据是存储到ActivityClientRecord中，也就是存到应用本身的进程中了

3. onSaveInstanceState存到系统进程中，所以App被杀之后还是能恢复的。而onRetainNonConfigurationInstance存到本身进程中，App被杀是没法恢复的。

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