Android S startActivity 启动流程分析

Activity中startActivity会执行Instrumentation.execStartActivity()的方法

public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
        //------省略一些代码
        try {
            intent.migrateExtraStreamToClipData(who);
            intent.prepareToLeaveProcess(who);
            int result = ActivityTaskManager.getService().startActivity(whoThread,
                    who.getOpPackageName(), who.getAttributionTag(), 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;
    }

接下来会执行ActivityTaskManagerService的startActivity方法

@Override
    public final int startActivity(IApplicationThread caller, String callingPackage,
            String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
            String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
            Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
                resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
                UserHandle.getCallingUserId());
    }

接下来通过ActivityStartController获取ActivityStarter执行execute()方法。然后对activity的flag和
权限做些检查，最终会调用startActivityUnchecked()->startActivityInner()。ActivityStarter 通过task startActivityLocked()

RootWindowContainer.resumeFocusedTasksTopActivities
resumeTopActivityInnerLocked -> ActivityTaskSupervisor.startSpecificActivity

ActivityTaskSupervisor.realStartActivityLocked

boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,
            boolean andResume, boolean checkConfig) throws RemoteException {
            // 省略一些代码
                // Create activity launch transaction.
                final ClientTransaction clientTransaction = ClientTransaction.obtain(
                        proc.getThread(), r.appToken);

                final boolean isTransitionForward = r.isTransitionForward();
                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, proc.getReportedProcState(),
                        r.getSavedState(), r.getPersistentSavedState(), results, newIntents,
                        r.takeOptions(), isTransitionForward,
                        proc.createProfilerInfoIfNeeded(), r.assistToken, activityClientController,
                        r.createFixedRotationAdjustmentsIfNeeded(), r.shareableActivityToken,
                        r.getLaunchedFromBubble()));
    }

clientTransactionHandler的是实现类是ActivityThread

@Override
    public void execute(ClientTransactionHandler client, IBinder token,
            PendingTransactionActions pendingActions) {
        Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
        ActivityClientRecord r = client.getLaunchingActivity(token);
        client.handleLaunchActivity(r, pendingActions, null );
        Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
    }

最后在ActivityThread调用一系列方法。