【移動應(yīng)用開發(fā)技術(shù)】Android Framework ActivityManagerService

【移動應(yīng)用開發(fā)技術(shù)】AndroidFrameworkActivityManagerService

ActivityManagerServiceActivityManagerService（簡稱：AMS）管理著應(yīng)用程序中創(chuàng)建的所有組件(Activity、Service等)，每個組件的信息與組件對應(yīng)的進(jìn)程信息都在管理范圍內(nèi)，包括內(nèi)存釋放潛規(guī)則。為了實(shí)現(xiàn)組件的管理，每個組件的狀態(tài)變化都需要通知AMS，組件間的跨進(jìn)程通信(IPC)也由AMS來搭建。所以AMS相當(dāng)重要，在源碼中隨處可見。先看下AMS靜態(tài)類結(jié)構(gòu)圖：舉例：啟動Activity時類圖對象的交互1.啟動activity，看以下源碼：Instrumentation.ActivityResult

ar

=

mInstrumentation.execStartActivity(

this,

mMainThread.getApplicationThread(),

mToken,

this,

intent,

requestCode);InstrumenttaionexecStartActivity源碼如下：int

result

=

ActivityManagerNative.getDefault()

.startActivity(whoThread,

intent,

intent.resolveTypeIfNeeded(who.getContentResolver()),

null,

0,

token,

target

!=

null

?

target.mEmbeddedID

:

null,

requestCode,

false,

false,

null,

null,

false);代碼中ActivityManagerNative.getDefault()得到是什么？看如下源碼：

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);

if

(false)

{

Log.v("ActivityManager",

"default

service

=

"

+

am);

}

return

am;

}

};

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);

}代碼中Singleton可看成是單例的一個模板，getDefault()返回的是gDefault.get()是返回Singleton.create的結(jié)果，在create方法中通過ServiceManager.getService("activity")所得到的對象既是AMS對象，從類圖中可以看出AMS也是一個IBinder對象，得到AMS對象之后調(diào)用了asInterface方法為其使用遠(yuǎn)程代理即：ActivityManagerProxy。那么得出結(jié)論是ActivityManagerNative.getDefault()得到是ActivityManagerProxy對象，緊接著調(diào)用ActivityManagerProxy.startActivity?？匆幌略创a：

public

int

startActivity(IApplicationThread

caller,

Intent

intent,

String

resolvedType,

Uri[]

grantedUriPermissions,

int

grantedMode,

IBinder

resultTo,

String

resultWho,

int

requestCode,

boolean

onlyIfNeeded,

boolean

debug,

String

profileFile,

ParcelFileDescriptor

profileFd,

boolean

autoStopProfiler)

throws

RemoteException

{

Parcel

data

=

Parcel.obtain();

Parcel

reply

=

Parcel.obtain();

data.writeInterfaceToken(IActivityManager.descriptor);

data.writeStrongBinder(caller

!=

null

?

caller.asBinder()

:

null);

intent.writeToParcel(data,

0);

data.writeString(resolvedType);

data.writeTypedArray(grantedUriPermissions,

0);

data.writeInt(grantedMode);

...

mRemote.transact(START_ACTIVITY_TRANSACTION,

data,

reply,

0);

reply.readException();

int

result

=

reply.readInt();

reply.recycle();

data.recycle();

return

result;

}可以看出ActivityManagerProxy負(fù)責(zé)將形參打包到parcel并調(diào)用mRemote.transact發(fā)送START_ACTIVITY_TRANSACTION指令，屆時的mRemote對象既是AMS對象。AMS對象繼承ActivityManagerNative，ActivityManagerNative實(shí)現(xiàn)了onTransact，負(fù)責(zé)接受mRemote.transact發(fā)送的parcel包。并根據(jù)code即：START_ACTIVITY_TRANSACTION，調(diào)用AMS的實(shí)現(xiàn)startActivity方法。屆時，通過ActivityManagerPro