Android知识总结

一、Activity的启动过程

Activity 启动流程图

• ActivityManagerService：activity的启动以及生命周期都统一由ActivityManagerService管理，而ActivityManagerService处于SystemServer进程中，应用程序进程通过Binder机制与SystemServer进程进行通信。

• ActivityManagerProxy：是ActivityManagerService在客户端的代理，客户端通过ActivityManageProxy间接调用ActivityManagerService。

• ActivityThread：应用程序的主线程ActivityThread，也是应用程序的入口；消息循环机制的创建、初始化信息等都在ActivityThread中完成。

• ApplicationThread：用来实现ActivityManagerService与ActivityThread之间的交互。在ActivityManagerService需要管理相关Application中的Activity的生命周期时，通过ApplicationThread的代理对象与ActivityThread通讯。

• ApplicationThreadProxy：是ApplicationThread在服务器端的代理，负责和客户端的ApplicationThread通讯。AMS就是通过该代理与ActivityThread进行通信的。

• Instrumentation：每一个应用程序只有一个Instrumentation对象，每个Activity内都有一个对该对象的引用。Instrumentation可以理解为应用进程的管家，ActivityThread要创建或暂停某个Activity时，都需要通过Instrumentation来进行具体的操作。

1.1、Launcher请求AMS阶段

Launcher请求AMS阶段

1.2、AMS到ApplicationThread阶段

AMS到ApplicationThread阶段

1.3、ApplicationThread到Activity阶段

ApplicationThread到Activity阶段

API28重构之后

二、判断Activity是否注册

在哪儿判断Activity是否在AndroidManifest.xml里面注册的？
首先没有在AndroidManifest.xml注册，报错是什么样子的

• 我们看 Instrumentation 的 execStartActivity方法

    public ActivityResult execStartActivity(
        Context who, IBinder contextThread, IBinder token, String 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);
                    ActivityResult result = null;
                    if (am.ignoreMatchingSpecificIntents()) {
                        result = am.onStartActivity(intent);
                    }
                    if (result != null) {
                        am.mHits++;
                        return result;
                    } else if (am.match(who, null, intent)) {
                        am.mHits++;
                        if (am.isBlocking()) {
                            return requestCode >= 0 ? am.getResult() : null;
                        }
                        break;
                    }
                }
            }
        }
        try {
            intent.migrateExtraStreamToClipData(who);
            intent.prepareToLeaveProcess(who);
            //1.通过IActivityManager调用我们执行AMS的startActivity方法，并返回执行结果
            int result = ActivityTaskManager.getService().startActivity(whoThread,
                    who.getBasePackageName(), who.getAttributionTag(), intent,
                    intent.resolveTypeIfNeeded(who.getContentResolver()), token, target,
                    requestCode, 0, null, options);
            //2. 检查结果
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }

接下来看checkStartActivityResult方法

    public static void checkStartActivityResult(int res, Object intent) {
        if (!ActivityManager.isStartResultFatalError(res)) {
            return;
        }

        switch (res) {
            case ActivityManager.START_INTENT_NOT_RESOLVED:
            case ActivityManager.START_CLASS_NOT_FOUND:
                //3. 这里我们找到了报错的地方，原来是res结果为START_INTENT_NOT_RESOLVED，
                //START_CLASS_NOT_FOUND就会报这个错误
                if (intent instanceof Intent && ((Intent)intent).getComponent() != null)
                    throw new ActivityNotFoundException(
                            "Unable to find explicit activity class "
                            + ((Intent)intent).getComponent().toShortString()
                            + "; have you declared this activity in your AndroidManifest.xml?");
                throw new ActivityNotFoundException(
                        "No Activity found to handle " + intent);
            case ActivityManager.START_PERMISSION_DENIED:
                throw new SecurityException("Not allowed to start activity "
                        + intent);
            case ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT:
                throw new AndroidRuntimeException(
                        "FORWARD_RESULT_FLAG used while also requesting a result");
            case ActivityManager.START_NOT_ACTIVITY:
                throw new IllegalArgumentException(
                        "PendingIntent is not an activity");
            case ActivityManager.START_NOT_VOICE_COMPATIBLE:
                throw new SecurityException(
                        "Starting under voice control not allowed for: " + intent);
            case ActivityManager.START_VOICE_NOT_ACTIVE_SESSION:
                throw new IllegalStateException(
                        "Session calling startVoiceActivity does not match active session");
            case ActivityManager.START_VOICE_HIDDEN_SESSION:
                throw new IllegalStateException(
                        "Cannot start voice activity on a hidden session");
            case ActivityManager.START_ASSISTANT_NOT_ACTIVE_SESSION:
                throw new IllegalStateException(
                        "Session calling startAssistantActivity does not match active session");
            case ActivityManager.START_ASSISTANT_HIDDEN_SESSION:
                throw new IllegalStateException(
                        "Cannot start assistant activity on a hidden session");
            case ActivityManager.START_CANCELED:
                throw new AndroidRuntimeException("Activity could not be started for "
                        + intent);
            default:
                throw new AndroidRuntimeException("Unknown error code "
                        + res + " when starting " + intent);
        }
    }

    private final void validateNotAppThread() {
        if (Looper.myLooper() == Looper.getMainLooper()) {
            throw new RuntimeException(
                "This method can not be called from the main application thread");
        }
    }