AIDL总结

最新推荐文章于 2023-04-12 16:26:09 发布

转载最新推荐文章于 2023-04-12 16:26:09 发布 · 904 阅读

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本文详细介绍了 Android 进程间通信（IPC）的重要组件 AIDL 的使用方法与注意事项，包括接口定义规范、异常处理机制等内容。

AIDL定义时的注意事项：

（1）接口名和aidl文件名相同.

（2）接口和方法前不用加访问权限修饰符public,private,protected等,也不能用final,static.

（3）AIDL默认支持的类型包话java基本类型(int,long,boolean等)和(String,List,Map,CharSequence),使用这些类型时不需要import声明.对于List和Map中包含的元素类型必须是AIDL支持的类型.如果使用自定义类型作为参数或返回值,自定义类型必须实现Parcelable接口.

（4）自定义类型和AIDL生成的其它接口类型在aidl描述文件中,应该显式import,即使在同一个包中.

（5）在aidl文件中所有非Java基本类型参数必须加上in、out、inout标记,以指明参数是输入参数、输出参数还是输入输出参数.

（6）Java原始类型默认的标记为in,不能为其它标记.

（7）oneway 关键字的使用：当接口使用oneway关键字修饰时，表示接口在远程调用时是不会block的，即接口调用时发送完transaction数据后立即返回而不会等待远端的结果。注意，这只针对IPC的调用，同样的接口如果是在同一进程内部被调用的话，oneway关键字不起任何效果，方法该阻塞就阻塞。

AIDL只支持接口方法，不能公开static变量。

抛出的异常是不能返回给调用者（跨进程抛异常处理是不可取的）。但是如果服务端有异常，客户端会收到RemoteException??

关于RemoteException，在StackOverflow上有一段讲述：

http://stackoverflow.com/questions/3156389/android-remoteexceptions-and-services

These exceptions do indeed get thrown and you should write appropriate try/catch logic to handle the situation where a remote method you invoked on a service did not complete.

As far as your investigation, you were on the right track looking through the native sources. What you may have overlooked is thatandroid.os.RemoteException is a actually just a base class for other Binder related exceptions and that it is a subclass,android.os.DeadObjectException, which is thrown within the native code of Binder.

An activity will see this exception if it makes use of a service running in another process that dies in the middle of performing a request. I was able to prove this to myself by making the following minor changes toMarko Gargenta's AIDLDemo example.

First, make sure the service runs in its own process by updating the AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.marakana" android:versionCode="1" android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name"
        android:theme="@android:style/Theme.Light">
        <activity android:name=".AIDLDemo" android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        
        <service android:name=".AdditionService" android:process=":process2"/>
    </application>
    <uses-sdk android:minSdkVersion="3" />
</manifest>

Then modify the add method to exit prematurely:

@Override
public IBinder onBind(Intent intent) {

    return new IAdditionService.Stub() {
        /**
         * Implementation of the add() method
         */
        public int add(int value1, int value2) throws RemoteException {
            Log.d(TAG, String.format("AdditionService.add(%d, %d)", value1,
                    value2));

            System.exit(-1); // KILL THE PROCESS BEFORE IT CAN RESPOND

            return value1 + value2;
        }

    };
}

In logcat you see the service process die, the activity receive a DeadObjectException, and ultimately the system respawn the service process.

D/AdditionService( 1379): AdditionService.add(1, 1)
I/AndroidRuntime( 1379): AndroidRuntime onExit calling exit(-1)
D/Zygote (   32): Process 1379 exited cleanly (255)
I/ActivityManager(   58): Process com.marakana:process2 (pid 1379) has died.
W/ActivityManager(   58): Scheduling restart of crashed service com.marakana/.AdditionService in 5000ms
D/AIDLDemo( 1372): onClick failed with: android.os.DeadObjectException
W/System.err( 1372): android.os.DeadObjectException
W/System.err( 1372):    at android.os.BinderProxy.transact(Native Method)
W/System.err( 1372):    at com.marakana.IAdditionService$Stub$Proxy.add(IAdditionService.java:95)
W/System.err( 1372):    at com.marakana.AIDLDemo$1.onClick(AIDLDemo.java:81)
W/System.err( 1372):    at android.view.View.performClick(View.java:2408)
W/System.err( 1372):    at android.view.View$PerformClick.run(View.java:8816)
W/System.err( 1372):    at android.os.Handler.handleCallback(Handler.java:587)
W/System.err( 1372):    at android.os.Handler.dispatchMessage(Handler.java:92)
W/System.err( 1372):    at android.os.Looper.loop(Looper.java:123)
W/System.err( 1372):    at android.app.ActivityThread.main(ActivityThread.java:4627)
W/System.err( 1372):    at java.lang.reflect.Method.invokeNative(Native Method)
W/System.err( 1372):    at java.lang.reflect.Method.invoke(Method.java:521)
W/System.err( 1372):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
W/System.err( 1372):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
W/System.err( 1372):    at dalvik.system.NativeStart.main(Native Method)
D/AIDLDemo( 1372): onServiceDisconnected() disconnected
I/ActivityManager(   58): Start proc com.marakana:process2 for service com.marakana/.AdditionService: pid=1399 uid=10037 gids={1015}
D/AdditionService( 1399): onCreate()
D/AIDLDemo( 1372): onServiceConnected() connected

I would imagine if your service was running in the same process as your activity you might never see this exception but then again if that were the case you probably wouldn't be bothering with AIDL.

Additionally, as you discovered, Android does not tunnel exceptions between processes. If you need to communicate an error back to a calling activity then you need to use other means