直接通過Binder的onTransact完成跨進程通信

1.具體代碼：

服務端實現：

public class IPCService extends Service {
 
    private static final String DESCRIPTOR = "IPCService";
    private final String[] names = { "B神", "艹神", "基神", "J神", "翔神" };
    private MyBinder mBinder = new MyBinder();
 
    private class MyBinder extends Binder {
        @Override
        protected boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
            switch (code) {
            case 0x001: {
                data.enforceInterface(DESCRIPTOR);
                int num = data.readInt();
                reply.writeNoException();
                reply.writeString(names[num]);
                return true;
            }
            }
            return super.onTransact(code, data, reply, flags);
        }
    }
 
    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }
}

可以看到onTransact有四個參數 
code ， data ，replay ， flags

• code 是一個整形的唯一標識，用於區分執行哪個方法，客戶端會傳遞此參數，告訴服務端執行哪個方法;
• data客戶端傳遞過來的參數;
• replay伺服器返回回去的值;
• flags標明是否有返回值，0為有（雙向），1為沒有（單向）。

客戶端實現：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 
    private EditText edit_num;
    private Button btn_query;
    private TextView txt_result;
    private IBinder mIBinder;
    private ServiceConnection PersonConnection = new ServiceConnection() {
        @Override
        public void onServiceDisconnected(ComponentName name) {
            mIBinder = null;
        }
 
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            mIBinder = service;
        }
    };
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bindViews();
 
        // 綁定遠程Service
        Intent service = new Intent("android.intent.action.IPCService");
        service.setPackage("com.jay.ipcserver");
        bindService(service, PersonConnection, BIND_AUTO_CREATE);
        btn_query.setOnClickListener(this);
    }
 
    private void bindViews() {
        edit_num = (EditText) findViewById(R.id.edit_num);
        btn_query = (Button) findViewById(R.id.btn_query);
        txt_result = (TextView) findViewById(R.id.txt_result);
    }
 
    @Override
    public void onClick(View v) {
        int num = Integer.parseInt(edit_num.getText().toString());
        if (mIBinder == null) {
            Toast.makeText(this, "未連接服務端或服務端被異常殺死", Toast.LENGTH_SHORT).show();
        } else {
            android.os.Parcel _data = android.os.Parcel.obtain();
            android.os.Parcel _reply = android.os.Parcel.obtain();
            String _result = null;
            try {
                _data.writeInterfaceToken("IPCService");
                _data.writeInt(num);
                mIBinder.transact(0x001, _data, _reply, 0);
                _reply.readException();
                _result = _reply.readString();
                txt_result.setText(_result);
                edit_num.setText("");
            } catch (RemoteException e) {
                e.printStackTrace();
            } finally {
                _reply.recycle();
                _data.recycle();
            }
        }
    }
}

2.transact和onTransact的區別

談transact 和onTransact需要先聊聊iBinder

IBinder是什麼呢？首先要明白，Android的遠程調用（就是跨進程調用）就是通過IBinder實現的，下麵是對android開發文檔的翻譯。

　　IBinder是遠程對象的基本介面，是為高性能而設計的輕量級遠程調用機制的核心部分。但它不僅用於遠程調用，也用於進程內調用。這個介面定義了與遠程對象交互的協議。不要直接實現這個介面，而應該從Binder派生。