AIDL設計思路

AIDL設計思路

AIDL

1.實現一個自定義的AIDL

// IMyService.aidl
package com.yetao.testaidl;

interface IMyService {
    /**
     * 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);
}

上面聲明瞭aidl接口、帶基礎數據類型的方法

2.IDE自動生成IMyService.java文件

    /*
 * This file is auto-generated.  DO NOT MODIFY.
 */
package com.yetao.testaidl;
// Declare any non-default types here with import statements

public interface IMyService extends android.os.IInterface {
    /**
     * IMyService的默認實現
     */
    public static class Default implements com.yetao.testaidl.IMyService {
        /**
         * Demonstrates some basic types that you can use as parameters
         * and return values in AIDL.
         */
        @Override
        public int basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException {
            return 0;
        }

        @Override
        public android.os.IBinder asBinder() {
            return null;
        }
    }

    /**
     * 本地IPC需要實現子類
     */
    public static abstract class Stub extends android.os.Binder implements com.yetao.testaidl.IMyService {
        private static final java.lang.String DESCRIPTOR = "com.yetao.testaidl.IMyService";

        /**
         * 構造函數，將標識符賦給當前對象
         */
        public Stub() {
            this.attachInterface(this, DESCRIPTOR);
        }

        /**
         *將IBinder對象轉換爲com.yetao.testaidl.IMyService接口，並在需要時生成代理。
        */
        public static com.yetao.testaidl.IMyService asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            //通過DESCRIPTOR查找本地是否有對應接口
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            //如果本地找到了，就返回
            if (((iin != null) && (iin instanceof com.yetao.testaidl.IMyService))) {
                return ((com.yetao.testaidl.IMyService) iin);
            }
            //沒有的話，就構建遠程代理對象
            return new com.yetao.testaidl.IMyService.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 {
            java.lang.String descriptor = DESCRIPTOR;
            switch (code) {
                case INTERFACE_TRANSACTION: {
                    reply.writeString(descriptor);
                    return true;
                }
                case TRANSACTION_basicTypes: {
                    data.enforceInterface(descriptor);
                    int _arg0;
                    _arg0 = data.readInt();
                    long _arg1;
                    _arg1 = data.readLong();
                    boolean _arg2;
                    _arg2 = (0 != data.readInt());
                    float _arg3;
                    _arg3 = data.readFloat();
                    double _arg4;
                    _arg4 = data.readDouble();
                    java.lang.String _arg5;
                    _arg5 = data.readString();
                    int _result = this.basicTypes(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5);
                    reply.writeNoException();
                    reply.writeInt(_result);
                    return true;
                }
                default: {
                    return super.onTransact(code, data, reply, flags);
                }
            }
        }

        private static class Proxy implements com.yetao.testaidl.IMyService {
            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;
            }

            /**
             * 演示一些基本類型，您可以將它們用作參數並在AIDL中返回值。
             */
            @Override
            public int basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                int _result;
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    _data.writeInt(anInt);
                    _data.writeLong(aLong);
                    _data.writeInt(((aBoolean) ? (1) : (0)));
                    _data.writeFloat(aFloat);
                    _data.writeDouble(aDouble);
                    _data.writeString(aString);
                    boolean _status = mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);
                    if (!_status && getDefaultImpl() != null) {
                        return getDefaultImpl().basicTypes(anInt, aLong, aBoolean, aFloat, aDouble, aString);
                    }
                    _reply.readException();
                    _result = _reply.readInt();
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
                return _result;
            }

            public static com.yetao.testaidl.IMyService sDefaultImpl;
        }

        //方法對應Id，依次增加
        static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);

        public static boolean setDefaultImpl(com.yetao.testaidl.IMyService impl) {
            if (Stub.Proxy.sDefaultImpl == null && impl != null) {
                Stub.Proxy.sDefaultImpl = impl;
                return true;
            }
            return false;
        }

        public static com.yetao.testaidl.IMyService getDefaultImpl() {
            return Stub.Proxy.sDefaultImpl;
        }
    }

    /**
     * 演示一些基本類型，您可以將它們用作參數並在AIDL中返回值。
     */
    public int basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException;

}

自動生成的java類，主要有以下幾個功能：
1.生成接口類IMyService（實現了IInterface接口來轉換成Binder對象）
2.生成一個默認實現類Default（IMyService的實現類）
3.生成本地IPC的實現類-Stub（Binder子類,實現IMyService接口），用於本地實現對應的Binder服務，避免不必要的遠程IPC通信，同時也能兼顧本地提供服務
4.生成遠端IPC的實現類-Proxy（實現IMyService接口），通過傳入的遠程Binder對象，調用transact()和遠端通信，然後獲取reply返回值

3.本地IPC-Stub本地的使用

public class AidlService extends Service {

    private IMyService.Stub stub = new IMyService.Stub() {
        @Override
        public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, String aString) throws RemoteException {

        }
    };


    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return stub;
    }
}

上面主要做了：
1.繼承IMyService.Stub，實現basicTypes方法
2.將stub對象賦值給Service的onBind()綁定，這也是爲什麼IMyService.Stub要繼承Binder的原因，需要來兼容本地IPC

4.遠端IPC使用

public class ClientActivity extends AppCompatActivity {

    private IMyService aidlService;

    private boolean connected;

    private void bindMyService() {
        ServiceConnection serviceConnection = new ServiceConnection() {
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                aidlService = IMyService.Stub.asInterface(service);
                connected = true;
            }

            @Override
            public void onServiceDisconnected(ComponentName name) {
                connected = false;
            }
        };
        //遠端訪問應該使用隱式啓動，這裏爲了方便，使用顯式調用
        Intent intent = new Intent(this, AidlService.class);
        bindService(intent,serviceConnection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bindMyService();
        initListener();
    }

    private void initListener() {
        findViewById(R.id.fab).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(connected){
                    try {
                        aidlService.basicTypes(1,2,false,0f,0,"sa");
                    } catch (RemoteException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
    }
}

使用第三部的AidlService，上面做了幾步：
1.構建連接回調ServiceConnection，監聽onServiceConnected()方法，獲取到遠端的binder對象，轉換爲IMyService類型對象
2.傳入ServiceConnection啓動服務，供回調
3.點擊按鈕，通過獲取到的binder對象（IMyService）調用遠端方法做交互

5.aidl整體流程

從basicTypes() -> transact() -> onTransact() 來進行分析

上面Proxy中的basicTypes()裏面調用Binder對象的transact()方法

Binder.java

    /**
     * 默認實現倒回包裹並在onTransact上調用。在遠端，將調用交易到活頁夾中以進行IPC。
     */
    public final boolean transact(int code, @NonNull Parcel data, @Nullable Parcel reply,
            int flags) throws RemoteException {
        if (false) Log.v("Binder", "Transact: " + code + " to " + this);

        if (data != null) {
            data.setDataPosition(0);
        }
        boolean r = onTransact(code, data, reply, flags);
        if (reply != null) {
            reply.setDataPosition(0);
        }
        return r;
    }

1.調用服務端的Binder對象實現的onTransact方法
2.設置數據位置爲0

來看Service中繼承的Stub的類

public static abstract class Stub extends android.os.Binder implements com.yetao.testaidl.IMyService {
        private static final java.lang.String DESCRIPTOR = "com.yetao.testaidl.IMyService";
        ``````省略無關代碼

        @Override
        public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException {
            java.lang.String descriptor = DESCRIPTOR;
            switch (code) {
                case INTERFACE_TRANSACTION: {
                    reply.writeString(descriptor);
                    return true;
                }
                case TRANSACTION_basicTypes: {
                    data.enforceInterface(descriptor);
                    int _arg0;
                    _arg0 = data.readInt();
                    long _arg1;
                    _arg1 = data.readLong();
                    boolean _arg2;
                    _arg2 = (0 != data.readInt());
                    float _arg3;
                    _arg3 = data.readFloat();
                    double _arg4;
                    _arg4 = data.readDouble();
                    java.lang.String _arg5;
                    _arg5 = data.readString();
                    int _result = this.basicTypes(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5);
                    reply.writeNoException();
                    reply.writeInt(_result);
                    return true;
                }
                default: {
                    return super.onTransact(code, data, reply, flags);
                }
            }
        }
        `````
}

主要步驟：
1.客戶端調用transact()發送TRANSACTION_basicTypes（code）後，服務端onTransact()接受到
2.從data讀出客戶端傳過來的數據
3.調用對應實現方法（basicTypes）獲取到返回值，寫入到reply；如果沒有返回值，則不寫入

小結，截止目前，瞭解到了在應用層aidl使用所做的流程，將在下一篇說明具體Binder驅動是怎麼交互的