Android S startActivity 启动流程分析

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()
com.android.server.wm.Task#.startActivityLocked ->ensureActivitiesVisible

在执行EnsureVisibleActivitiesConfigHelper.processActivity

void process(ActivityRecord start, boolean preserveWindow) {
            if (start == null || !start.mVisibleRequested) {
                return;
            }
            reset(preserveWindow);

            final PooledFunction f = PooledLambda.obtainFunction(
                    EnsureVisibleActivitiesConfigHelper::processActivity, this,
                    PooledLambda.__(ActivityRecord.class));
            forAllActivities(f, start, true /*includeBoundary*/, true /*traverseTopToBottom*/);
            f.recycle();

            if (mUpdateConfig) {
                // Ensure the resumed state of the focus activity if we updated the configuration of
                // any activity.
                mRootWindowContainer.resumeFocusedTasksTopActivities();
            }
        }

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 /* customIntent */);
        Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
    }

最后在ActivityThread的hanleLaunchActivity 和 performLaunchActivity。通过mInstrumentation创建activity的实例，获取Application的实例（如果不存在的话，调用instrumentation.newApplication创建application实例），调用activity.attach方法。

handleResumeActivity是怎么触发的？

hanleLaunchActivity 之后通过TransactionExecutor 执行ResumeActivityItem的execute方法。执行handleResumeActivity方法。