Android5.0 Framework - Activity启动过程（二）

标签（空格分隔）： Android Framework

1. 前言

在Android Framework - Activity启动过程（一）中追踪源码到Instrumentation类中,那么Instrumentation到底如何启动Activity？

2. Instrumentation类

 public ActivityResult execStartActivity(            Context who, IBinder contextThread, IBinder token, Activity target,            Intent intent, int requestCode, Bundle options) {        IApplicationThread whoThread = (IApplicationThread) contextThread;        if (mActivityMonitors != null) {            synchronized (mSync) {                //遍历查询，是否存在这个Activity                final int N = mActivityMonitors.size();                for (int i=0; i<N; i++) {                    final ActivityMonitor am = mActivityMonitors.get(i);                    if (am.match(who, null, intent)) {                        am.mHits++;                        //Activity如果打不开，这直接return                        if (am.isBlocking()) {                            return requestCode >= 0 ? am.getResult() : null;                        }                        break;                    }                }            }        }        try {            intent.migrateExtraStreamToClipData();            intent.prepareToLeaveProcess();            //打开activity            //ActivityManagerNative.getDefault()就是ActivityManagerProxy对象            //ActivityManagerProxy就是进程通信代理对象            //ActivityManagerProxy对象再通过IBinder关联到ActivityManagerService            int result = ActivityManagerNative.getDefault()                .startActivity(whoThread, who.getBasePackageName(), intent,                        intent.resolveTypeIfNeeded(who.getContentResolver()),                        token, target != null ? target.mEmbeddedID : null,                        requestCode, 0, null, options);            //检测打开的activity,会抛各种异常            checkStartActivityResult(result, intent);        } catch (RemoteException e) {        }        return null;    }

• ActivityManagerNative.getDefault()返回的是ActivityManagerProxy对象
• 重点在于ActivityManagerNative.getDefault()
  .startActivity（…）方法
• 顺便看一下 checkStartActivityResult(result, intent);是干什么的？

那么ActivityManagerNative.getDefault()为什么返回的是ActivityManagerProxy对象呢？那么打开ActivityManagerNative源码来看一下

    /**     * Retrieve the system's default/global activity manager.     */    static public IActivityManager getDefault() {        return gDefault.get();    }

那么gDefault又是什么呢？返回的是IActivityManager

    private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {        protected IActivityManager create() {            //代理类            IBinder b = ServiceManager.getService("activity");            if (false) {                Log.v("ActivityManager", "default service binder = " + b);            }            IActivityManager am = asInterface(b);            if (false) {                Log.v("ActivityManager", "default service = " + am);            }            return am;        }    };}

那么IActivityManager又是什么呢?

   static public IActivityManager asInterface(IBinder obj) {        if (obj == null) {            return null;        }        IActivityManager in =            (IActivityManager)obj.queryLocalInterface(descriptor);        if (in != null) {            return in;        }        return new ActivityManagerProxy(obj);    }

从源码中 return new ActivityManagerProxy(obj);可见返回的就是 ActivityManagerProxy对象;

2.checkStartActivityResult(result, intent)

 public static void checkStartActivityResult(int res, Object intent) {        if (res >= ActivityManager.START_SUCCESS) {            return;        }        switch (res) {            case ActivityManager.START_INTENT_NOT_RESOLVED:            case ActivityManager.START_CLASS_NOT_FOUND:                if (intent instanceof Intent && ((Intent)intent).getComponent() != null)                    //在xml中没有注册activity                    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);            default:                throw new AndroidRuntimeException("Unknown error code "                        + res + " when starting " + intent);        }    }

• 仔细一看，原打开activity的时候，这个方法检测异常的
• 其中常见的 Unable to find e···have you declared this activity in your AndroidManifest.xml?就是在xm中没有找到打开的Activity，需要在AndroidManifestxml中注册

3.ActivityManagerProxy类，说在前面

1. 打开ActivityManagerProxy类，发现是ActivityManagerNative类的内部类;

2. ActivityManagerProxy和ActivityManagerNative都实现IActivityManager这个接口

3. ActivityManagerNative是抽象类，ActivityManagerService继承ActivityManagerNative

3.ActivityManagerProxy类的实现

 public int startActivity(IApplicationThread caller, String callingPackage, Intent intent,            String resolvedType, IBinder resultTo, String resultWho, int requestCode,            int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException {        Parcel data = Parcel.obtain();        Parcel reply = Parcel.obtain();        data.writeInterfaceToken(IActivityManager.descriptor);        data.writeStrongBinder(caller != null ? caller.asBinder() : null);        data.writeString(callingPackage);        intent.writeToParcel(data, 0);        data.writeString(resolvedType);        data.writeStrongBinder(resultTo);        data.writeString(resultWho);        data.writeInt(requestCode);        data.writeInt(startFlags);        if (profilerInfo != null) {            data.writeInt(1);            profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);        } else {            data.writeInt(0);        }        if (options != null) {            data.writeInt(1);            options.writeToParcel(data, 0);        } else {            data.writeInt(0);        }        //通过Binder驱动程序就进入到ActivityManagerService的startActivity函数来        //mRemote是一个BinderProxy对象，transact方法本地化实现        mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);        reply.readException();        int result = reply.readInt();        reply.recycle();        data.recycle();        return result;    }

这里并没有处理，只是个代理，通过IBinder，最终将消息传递到ActivityManagerService中，让ActivityManagerService处理打开Activity.

那么ActivityManagerService到底如何启动Activity待续…