Android 学习 AIDL 的使用

Myth丶恋晨 2022-08-04 15:52 197阅读 0赞

今天，尝试这为Service 设定新的进程时，遇到了 Fatal 的Bug.  
AndroidManifest.xml 设置如下：

通过 process设置 Service 运行的进程 remote，当 startService运行service时，查看系统的进程，就会发现多了一个 remote 的进程。但，同时也遇到了新的问题，当 bindService时，抛出了如下的异常：

java.lang.ClassCastException: android.os.BinderProxy cannot be cast to demo.example.com.servicedemo.MyService$MyBinder
                at demo.example.com.servicedemo.MainActivity$1.onServiceConnected(MainActivity.java:50)
                at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1223)
                at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1240)
                at android.os.Handler.handleCallback(Handler.java:739)
                at android.os.Handler.dispatchMessage(Handler.java:95)
                at android.os.Looper.loop(Looper.java:148)
                at android.app.ActivityThread.main(ActivityThread.java:5417)
                at java.lang.reflect.Method.invoke(Native Method)
                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是 process引起的，当Activity与Service运行在不同的进程中时，如果要绑定二者，就会抛出这样的异常。但是如果我们有这样的需求，需要Activity 和Service 进行跨进程通信时，又该怎么办呢？  
可以使用AIDL封装Binder。

## 什么是 AIDL ##

AIDL: Android Interface Definition Language,即Android接口定义语言。

## 如何使用 AIDL ##

一， 定义 .aidl 文件

AIDL文件的格式类似与 Java 中的接口 interface，我们需要在我们的工程目录下创建一个以 .aidl 结尾的文件 IPerson.aidl.

// IMyAidlInterface.aidl
    interface IMyAidlInterface {
        String sayHello(String content);
    }

我们以 Android Studio为例，创建好之后，系统会自动生成一个文件进行进程间通信，类似与下面的格式

/*
     * This file is auto-generated.  DO NOT MODIFY.
     * Original file: /AIDLDemo/app/src/main/aidl/demo/example/com/aidldemo/IMyAidlInterface.aidl
     */
    package demo.example.com.aidldemo;
    // Declare any non-default types here with import statements
    
    public interface IMyAidlInterface extends android.os.IInterface
    {
        
    /** Local-side IPC implementation stub class. */
    public static abstract class Stub extends android.os.Binder implements demo.example.com.aidldemo.IMyAidlInterface
    {
        
    private static final java.lang.String DESCRIPTOR = "demo.example.com.aidldemo.IMyAidlInterface";
    /** Construct the stub at attach it to the interface. */
    public Stub()
    {
    this.attachInterface(this, DESCRIPTOR);
    }
    /**
     * Cast an IBinder object into an demo.example.com.aidldemo.IMyAidlInterface interface,
     * generating a proxy if needed.
     */
    public static demo.example.com.aidldemo.IMyAidlInterface asInterface(android.os.IBinder obj)
    {
    if ((obj==null)) {
    return null;
    }
    android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
    if (((iin!=null)&&(iin instanceof demo.example.com.aidldemo.IMyAidlInterface))) {
    return ((demo.example.com.aidldemo.IMyAidlInterface)iin);
    }
    return new demo.example.com.aidldemo.IMyAidlInterface.Stub.Proxy(obj);
    }
    @Override public android.os.IBinder asBinder()
    {
    return this;
    }
    @Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
    {
    switch (code)
    {
    case INTERFACE_TRANSACTION:
    {
    reply.writeString(DESCRIPTOR);
    return true;
    }
    case TRANSACTION_sayHello:
    {
    data.enforceInterface(DESCRIPTOR);
    java.lang.String _arg0;
    _arg0 = data.readString();
    java.lang.String _result = this.sayHello(_arg0);
    reply.writeNoException();
    reply.writeString(_result);
    return true;
    }
    }
    return super.onTransact(code, data, reply, flags);
    }
    private static class Proxy implements demo.example.com.aidldemo.IMyAidlInterface
    {
        
    private android.os.IBinder mRemote;
    Proxy(android.os.IBinder remote)
    {
    mRemote = remote;
    }
    @Override public android.os.IBinder asBinder()
    {
    return mRemote;
    }
    public java.lang.String getInterfaceDescriptor()
    {
    return DESCRIPTOR;
    }
    /**
         * Demonstrates some basic types that you can use as parameters
         * and return values in AIDL.
         *///void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
    //        double aDouble, String aString);
    
    @Override public java.lang.String sayHello(java.lang.String content) throws android.os.RemoteException
    {
    android.os.Parcel _data = android.os.Parcel.obtain();
    android.os.Parcel _reply = android.os.Parcel.obtain();
    java.lang.String _result;
    try {
    _data.writeInterfaceToken(DESCRIPTOR);
    _data.writeString(content);
    mRemote.transact(Stub.TRANSACTION_sayHello, _data, _reply, 0);
    _reply.readException();
    _result = _reply.readString();
    }
    finally {
    _reply.recycle();
    _data.recycle();
    }
    return _result;
    }
    }
    static final int TRANSACTION_sayHello = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
    }
    /**
         * Demonstrates some basic types that you can use as parameters
         * and return values in AIDL.
         *///void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
    //        double aDouble, String aString);
    
    public java.lang.String sayHello(java.lang.String content) throws android.os.RemoteException;
    }

二， 定义我们的Service文件，并定义返回对象

继承自 Service, 和之前类似，稍有不同的是我们需要实例化 IMyAidlInterface.Stub 方法，实现之前接口定义的方法。并在 onBind 中返回供客户端调用。

private IMyAidlInterface.Stub myAidlStub = new IMyAidlInterface.Stub() {
            @Override
            public String sayHello(String content) throws RemoteException {
                Toast.makeText(MyService.this, content, Toast.LENGTH_LONG).show();
                return content;
            }
        };
    
        @Override
        public IBinder onBind(Intent intent) {
            return myAidlStub;
        }

三， MainActivity 中获取 ConnectionService 引用。

private IMyAidlInterface myAidlInterface;
    
        ServiceConnection connection = new ServiceConnection() {
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                myAidlInterface = IMyAidlInterface.Stub.asInterface(service);
            }
    
            @Override
            public void onServiceDisconnected(ComponentName name) {
            }
        };

这样 Activity 就可以与远程 Service 进行通信了。