Android中的IPC方式——Binder（一）

在開發(fā)過程中冗懦，實現(xiàn)進程間通信用的最多的就是 AIDL情臭。

AIDL(Android Interface Definition Language)妖枚，也就是接口定義語言运提，提供接口給遠程調用者鳍寂。

當我們定義好 AIDL 文件改含，在編譯時編譯器會幫我們生成代碼實現(xiàn) IPC 通信。為了可以更好的理解Binder的過程迄汛，從AIDL入手捍壤。

服務端

先創(chuàng)建一個服務端骤视，創(chuàng)建一個IStudentManager.aidl文件,聲明2個方法getStudentList()以及addStudent()
IStudentManager.aidl

// IStudentManager.aidl
package com.golden.aidlserver;
import com.golden.aidlserver.Student;
// Declare any non-default types here with import statements

interface IStudentManager {
    List<Student> getStudentList();
    void addStudent(in Student student);
}

IStudentManager.java
Build一下工程，android studio會自動為我們生成一個java類：IStudentManager.java,大體結構如下鹃觉。

package com.golden.aidlserver;
// Declare any non-default types here with import statements

public interface IStudentManager extends android.os.IInterface {
    public static abstract class Stub extends android.os.Binder 
            implements com.golden.aidlserver.IStudentManager {
        private static final java.lang.String DESCRIPTOR = "com.golden.aidlserver.IStudentManager";

        public Stub() {
            this.attachInterface(this, DESCRIPTOR);
        }
        public static com.golden.aidlserver.IStudentManager asInterface(android.os.IBinder 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 {...}

        private static class Proxy implements com.golden.aidlserver.IStudentManager {
            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;
            }

            @Override
            public java.util.List<com.golden.aidlserver.Student> getStudentList() throws android.os.RemoteException {...}

            @Override
            public void addStudent(com.golden.aidlserver.Student student) throws android.os.RemoteException {...}

        static final int TRANSACTION_getStudentList = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
        static final int TRANSACTION_addStudent = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
    }

    public java.util.List<com.golden.aidlserver.Student> getStudentList() throws android.os.RemoteException;

    public void addStudent(com.golden.aidlserver.Student student) throws android.os.RemoteException;
}

該類首先包含了一個抽象內部類：Stub, 該類繼承自Binder并實現(xiàn)了IStudentManager接口专酗。在Stub的內部，又包含了一個靜態(tài)內部類：Proxy盗扇，Proxy類同樣實現(xiàn)了IStudentManager接口祷肯。

Sercvice

接下來創(chuàng)建一個StudentManagerService,需要實現(xiàn)剛剛我們定義的兩個方法,并且在AndroidManifest注冊。

public class StudentManagerService extends Service {
    private CopyOnWriteArrayList<Student>  mStudentList = new CopyOnWriteArrayList<>();
    @Override
    public void onCreate() {
        super.onCreate();
        mStudentList.add(1,"張三");
    }

    @Override
    public IBinder onBind(Intent intent) {
        return new MyBinder();
    }

    class MyBinder extends IStudentManager.Stub {
        @Override
        public List<Student> getStudentList() throws RemoteException {
            return mStudentList;
        }

        @Override
        public void addStudent(Student student) throws RemoteException {
            mStudentList.add(student);
        }
    }
}

 <service android:name=".StudentManagerService"
            android:process=":remote">
      <intent-filter>
          <!--是客戶端用于訪問AIDL服務的ID  -->
          <action android:name="com.golden.server.StudentManagerService" />
      </intent-filter>
</service>

客戶端

為了邏輯上區(qū)分清晰疗隶，另外重新創(chuàng)建一個客戶端的應用佑笋。需要將服務端的aidl以及Student.java拷貝到客戶端注意與服務端的包名保持一致

client項目結構

public class ClientMainActivity extends AppCompatActivity {
    private static final String TAG = "AIDL Client";
    private IStudentManager mRemoteStudentManager;

    private int size = 1;
    private Button mAddBtn;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAddBtn = findViewById(R.id.mButton);

        Intent intent = new Intent();
        intent.setComponent(new ComponentName("com.golden.aidlserver", "com.golden.aidlserver.StudentManagerService"));
        bindService(intent, mConnection, BIND_AUTO_CREATE);
        initView();
    }

    private void initView() {
        mAddBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    if (mRemoteStudentManager != null) {
                        mRemoteStudentManager.addStudent(new Student(size+1,"李四"+String.valueOf(size+1)));
                        List<Student> studentList = mRemoteStudentManager.getStudentList();
                        size = studentList.size();
                        Log.e(TAG,studentList.toString());
                    }
                } catch (RemoteException e) {

                    e.printStackTrace();
                }
            }
        });
    }

    private ServiceConnection mConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            Log.e(TAG, "onServiceConnected");
            //獲得IStudentManager對象
            mRemoteStudentManager = IStudentManager.Stub.asInterface(service);
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            Log.e(TAG, "onServiceDisconnected");
            mRemoteStudentManager = null;
        }
    };
}

client中去bindservice在onServiceConnected()中得到服務端獲得IStudentManager對象mRemoteStudentManager,可以通過mRemoteStudentManager來調用服務端service的方法。實現(xiàn)點擊button之后服務端添加一個學生然后getStudentList()打印出來抽减。

image

Stub

public static abstract class Stub extends android.os.Binder implements com.golden.aidlserver.IStudentManager {
    private static final java.lang.String DESCRIPTOR = "com.golden.aidlserver.IStudentManager";
    /**
     * Construct the stub at attach it to the interface.
     */
    public Stub() {
        this.attachInterface(this, DESCRIPTOR);
    }
    /**
     * Cast an IBinder object into an com.golden.aidlserver.IStudentManager interface,
     * generating a proxy if needed.
     */
    public static com.golden.aidlserver.IStudentManager asInterface(android.os.IBinder obj) {
        if ((obj == null)) {
            return null;
        }
        android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
        if (((iin != null) && (iin instanceof com.golden.aidlserver.IStudentManager))) {
            return ((com.golden.aidlserver.IStudentManager) iin);
        }
        return new com.golden.aidlserver.IStudentManager.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_getStudentList: {
                data.enforceInterface(descriptor);
                java.util.List<com.golden.aidlserver.Student> _result = this.getStudentList();
                reply.writeNoException();
                reply.writeTypedList(_result);
                return true;
            }
            case TRANSACTION_addStudent: {
                data.enforceInterface(descriptor);
                com.golden.aidlserver.Student _arg0;
                if ((0 != data.readInt())) {
                    _arg0 = com.golden.aidlserver.Student.CREATOR.createFromParcel(data);
                } else {
                    _arg0 = null;
                }
                this.addStudent(_arg0);
                reply.writeNoException();
                return true;
            }
            default: {
                return super.onTransact(code, data, reply, flags);
            }
        }
    static final int TRANSACTION_getStudentList = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
    static final int TRANSACTION_addStudent = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
}

stub結構

其中有一個DESCRIPTOR允青，它在Stub初始化的時候會綁定這個標識符，就是前面曾經提到的安全性方面卵沉。

client與server擁有一樣的IStudentManager.java文件,在client端我們可以看到

//client端
private ServiceConnection mConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        Log.e(TAG, "onServiceConnected");
        //獲得IStudentManager對象
        mRemoteStudentManager = IStudentManager.Stub.asInterface(service);
    }

    @Override
    public void onServiceDisconnected(ComponentName name) {
        Log.e(TAG, "onServiceDisconnected");
        mRemoteStudentManager = null;
    }
};

我們在 client端中bindservice中在onServiceConnected()會傳給我們一個IBinder颠锉，這個 IBinder類型的參數(shù)是Binder驅動傳給我們的，后面在framework的會說到史汗。方法中會去調用 binder.queryLocalInterface() 去查找 Binder 本地對象琼掠，如果找到了就說明 Client 和 Server 在同一進程，那么這個 binder 本身就是 Binder 本地對象停撞，可以直接使用瓷蛙。否則說明是 IBinder是個遠程對象，也就是 BinderProxy戈毒。因此需要我們創(chuàng)建一個代理對象 Proxy艰猬，通過這個代理對象來是實現(xiàn)遠程訪問。

server端中我們只是創(chuàng)建了stub的對象并且實現(xiàn)了其中定義的兩個方法埋市，等待調用onTransact()方法冠桃。

    //server端    
    class MyBinder extends IStudentManager.Stub {
            @Override
            public List<Student> getStudentList() throws RemoteException {
                return mStudentList;
            }

            @Override
            public void addStudent(Student student) throws RemoteException {
                mStudentList.add(student);
            }
    }

Proxy

在client中當client 和server處于不同的進程的情況下，client使用的是Proxy對象mRemote道宅。

private static class Proxy implements com.golden.aidlserver.IStudentManager {
    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;
    }

    @Override
    public java.util.List<com.golden.aidlserver.Student> getStudentList() throws android.os.RemoteException {
        android.os.Parcel _data = android.os.Parcel.obtain();
        android.os.Parcel _reply = android.os.Parcel.obtain();
        java.util.List<com.golden.aidlserver.Student> _result;
        try {
            _data.writeInterfaceToken(DESCRIPTOR);
            mRemote.transact(Stub.TRANSACTION_getStudentList, _data, _reply, 0);
            _reply.readException();
            _result = _reply.createTypedArrayList(com.golden.aidlserver.Student.CREATOR);
        } finally {
            _reply.recycle();
            _data.recycle();
        }
        return _result;
    }

    @Override
    public void addStudent(com.golden.aidlserver.Student student) throws android.os.RemoteException {
        android.os.Parcel _data = android.os.Parcel.obtain();
        android.os.Parcel _reply = android.os.Parcel.obtain();
        try {
            _data.writeInterfaceToken(DESCRIPTOR);
            if ((student != null)) {
                _data.writeInt(1);
                student.writeToParcel(_data, 0);
            } else {
                _data.writeInt(0);
            }
            mRemote.transact(Stub.TRANSACTION_addStudent, _data, _reply, 0);
            _reply.readException();
        } finally {
            _reply.recycle();
            _data.recycle();
        }
    }
}

單獨看下 client調用getStudentList()過程就是 proxy中調用食听。數(shù)據(jù)包_data需要將標識符DESCRIPTOR寫入，遠程調用mRemote.transact(Stub.TRANSACTION_getStudentList, _data, _reply, 0);（因性能考慮需要將方法以int值來標識）污茵，然后server端會調用到stub中的ontranscat()樱报，最后client中的proxy得到結果。

@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_getStudentList: {
            data.enforceInterface(descriptor);
            java.util.List<com.golden.aidlserver.Student> _result = this.getStudentList();
            reply.writeNoException();
            reply.writeTypedList(_result);
            return true;
        }
        case TRANSACTION_addStudent: {
            data.enforceInterface(descriptor);
            com.golden.aidlserver.Student _arg0;
            if ((0 != data.readInt())) {
            _arg0 = com.golden.aidlserver.Student.CREATOR.createFromParcel(data);
            } else {
            _arg0 = null;
            }
            this.addStudent(_arg0);
            reply.writeNoException();
            return true;
        }
        default: {
            return super.onTransact(code, data, reply, flags);
        }
    }
}

將_result 寫入 _replay中返回給客戶端泞当。如果是在同一個進程中迹蛤，就將直接調用stub中的getStudent()方法不會走transact()和onTransact()邏輯。

image

以上就是一個簡單的進程通信的流程，在不同進程的前提下笤受，在理解的時候可以把client的所有操作都是通過proxy來實現(xiàn)穷缤，server端就是stub的具體實現(xiàn)。

下一篇會講framework層源碼箩兽。