今天擼原始碼：startActivity()。

發現了在API 26中： ActivityManagerNative類被棄用，代理類ActivityManagerProxy已經被刪除。

本篇文章主要是記下，API26和API25的不同。

看到Instrumentation類的exeStartActivity時候，原始碼如下：

 public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
        IApplicationThread whoThread = (IApplicationThread) contextThread;
        Uri referrer = target != null ? target.onProvideReferrer() : null;
        if (referrer != null) {
            intent.putExtra(Intent.EXTRA_REFERRER, referrer);
        }
        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();
            intent.prepareToLeaveProcess(who);
            int result = ActivityManager.getService()//注意這一行，和參考文章不同！
                .startActivity(whoThread, who.getBasePackageName(), 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;
    }
 

怎麼兩句話不同呢？其實原來我使用的api是26，而26之前的程式碼使用的是原作者寫的。

繼續深入看兩個不同的程式碼：

26：

 /**
     * @hide
     */
    public static IActivityManager getService() {
        return IActivityManagerSingleton.get();
    }

    private static final Singleton<IActivityManager> IActivityManagerSingleton =
            new Singleton<IActivityManager>() {
                @Override
                protected IActivityManager create() {
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
                    final IActivityManager am = IActivityManager.Stub.asInterface(b);//注意這一行
                    return am;
                }
            };
 

 static public IActivityManager getDefault() {
        return gDefault.get();
    }

 private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
        protected IActivityManager create() {
            IBinder b = ServiceManager.getService("activity");
            if (false) {
                Log.v("ActivityManager", "default service binder = " + b);
            }
            IActivityManager am = asInterface(b);//注意這一行
            if (false) {
                Log.v("ActivityManager", "default service = " + am);
            }
            return am;
        }
    };
 

25中使用的是：靜態方法asInterface，該方法屬於ActivityManagerNative類。原始碼：   

 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);
    }

26中使用的是：

IActivityManager.Stub.asInterface(b);

而我們再看api26中的ActivityManagerNative類。原始碼已經很少：

/**
 * {@hide}
 * @deprecated will be removed soon. See individual methods for alternatives.//注意解釋
 */
@Deprecated
public abstract class ActivityManagerNative {
    /**
     * Cast a Binder object into an activity manager interface, generating
     * a proxy if needed.
     *
     * @deprecated use IActivityManager.Stub.asInterface instead.//注意解釋
     */
    static public IActivityManager asInterface(IBinder obj) {
        return IActivityManager.Stub.asInterface(obj);
    }

    /**
     * Retrieve the system's default/global activity manager.
     *
     * @deprecated use ActivityManager.getService instead.
     */
    static public IActivityManager getDefault() {
        return ActivityManager.getService();
    }

    /**
     * Convenience for checking whether the system is ready.  For internal use only.
     *
     * @deprecated use ActivityManagerInternal.isSystemReady instead.
     */
    static public boolean isSystemReady() {
        return ActivityManager.isSystemReady();
    }

    /**
     * @deprecated use ActivityManager.broadcastStickyIntent instead.
     */
    static public void broadcastStickyIntent(Intent intent, String permission, int userId) {
        broadcastStickyIntent(intent, permission, AppOpsManager.OP_NONE, userId);
    }

    /**
     * Convenience for sending a sticky broadcast.  For internal use only.
     * If you don't care about permission, use null.
     *
     * @deprecated use ActivityManager.broadcastStickyIntent instead.
     */
    static public void broadcastStickyIntent(Intent intent, String permission, int appOp,
            int userId) {
        ActivityManager.broadcastStickyIntent(intent, appOp, userId);
    }

    /**
     * @deprecated use ActivityManager.noteWakeupAlarm instead.
     */
    static public void noteWakeupAlarm(PendingIntent ps, int sourceUid, String sourcePkg,
            String tag) {
        ActivityManager.noteWakeupAlarm(ps, sourceUid, sourcePkg, tag);
    }

    /**
     * @deprecated use ActivityManager.noteAlarmStart instead.
     */
    static public void noteAlarmStart(PendingIntent ps, int sourceUid, String tag) {
        ActivityManager.noteAlarmStart(ps, sourceUid, tag);
    }

    /**
     * @deprecated use ActivityManager.noteAlarmFinish instead.
     */
    static public void noteAlarmFinish(PendingIntent ps, int sourceUid, String tag) {
        ActivityManager.noteAlarmFinish(ps, sourceUid, tag);
    }
}

而且代理類ActivityManagerProxy已經被刪除！

小結：API26中啟動Activity時候，和AMS通訊機制已經被改成AIDL方式！

擴充套件思考：

1、其實通過看aidl 自動生成檔案，可以看出，

stub.asInterface其實呼叫的也是queryLocalInterface，api25和api26的本質是一樣的。

2、api26中只有ServiceManagerNative還沒有被棄用。

25中使用的：

ApplicationThreadNative、
ActivityManagerNative、
BulkCursorNative、
ContentProviderNative、

都已經不在使用。