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[操作系统]AIDL使用解析


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之前面试的时候被问到这个问题,然而当时只有一个大致的印象,随GG,于是我就重新整理的一下。这里大力推荐《Android开发艺术探索》这本书,写的太好了!

1.AIDL

AIDL(Android Interface Define Language) 是IPC进程间通信方式的一种.用于生成可以在Android设备上两个进程之间进行进程间通信(interprocess communication, IPC)的代码.

2.AIDL和Messenger的区别:

  1. Messenger不适用大量并发的请求:Messenger以串行的方式来处理客户端发来的消息,如果大量的消息同时发送到服务端,服务端仍然只能一个个的去处理。
  2. Messenger主要是为了传递消息:对于需要跨进程调用服务端的方法,这种情景不适用Messenger。
  3. Messenger的底层实现是AIDL,系统为我们做了封装从而方便上层的调用。
  4. AIDL适用于大量并发的请求,以及涉及到服务端端方法调用的情况

3.使用AIDL的步骤:

下面一个简单的例子来说明AIDL的使用:假设一个情景我们需要计算a+b,我们需要在客户端传递两个参数a和b,然后将参数传递给服务端(另一个进程)来进行计算,计算结果传递给客户端。

目录结构


1. 新建一个项目作为服务端,在项目中新建AIDL文件。这里我命名为:IImoocAIDL.aidl

// IImoocAIDL.aidlpackage com.mecury.aidltest;// Declare any non-default types here with import statementsinterface IImoocAIDL {    //计算num1 + num2    int add(int num1,int num2);}

点击同步按钮(一定要先同步),查看是否生成IImoocAIDL文件。

aidl的生成.gif



生成的文件如下,我写了详细的注释,相信你能够看懂:

生成的AIDL文件#IImoocAIDL.java:

这里来说一下AIDL通信的原理:首先看这个文件有一个叫做proxy的类,这是一个代理类,这个类运行在客户端中,其实AIDL实现的进程间的通信并不是直接的通信,客户端和服务端都是通过proxy来进行通信的:客户端调用的方法实际是调用是proxy中的方法,然后proxy通过和服务端通信将返回的结果返回给客户端。

package com.mecury.aidltest;public interface IImoocAIDL extends android.os.IInterface {    public static abstract class Stub extends android.os.Binder implements com.mecury.aidltest.IImoocAIDL {    private static final java.lang.String DESCRIPTOR = "com.mecury.aidltest.IImoocAIDL";         public Stub() {      this.attachInterface(this, DESCRIPTOR);    }                public static com.mecury.aidltest.IImoocAIDL asInterface(android.os.IBinder obj) {      if ((obj == null)) {        return null;      }      android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);      if (((iin != null) && (iin instanceof com.mecury.aidltest.IImoocAIDL))) {        return ((com.mecury.aidltest.IImoocAIDL) iin);      }      return new com.mecury.aidltest.IImoocAIDL.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_add: {          data.enforceInterface(DESCRIPTOR);                    int _arg0;          _arg0 = data.readInt();          int _arg1;          _arg1 = data.readInt();                    int _result = this.add(_arg0, _arg1);                    reply.writeNoException();          reply.writeInt(_result);          return true;        }      }      return super.onTransact(code, data, reply, flags);     }        private static class Proxy implements com.mecury.aidltest.IImoocAIDL {      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 int add(int num1, int num2) 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(num1);          _data.writeInt(num2);                    mRemote.transact(Stub.TRANSACTION_add, _data, _reply, 0);          _reply.readException();          _result = _reply.readInt();        } finally {          _reply.recycle();          _data.recycle();        }        return _result;      }    }        static final int TRANSACTION_add = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);  }    public int add(int num1, int num2) throws android.os.RemoteException;}

代码中的几个方法:
DESCRIPTION
Binderd的唯一标识,一般用当前的类名表示。
asInterface(android.os.IBinder obj)
用于将服务端的Binder对象转换为客户端需要的AIDL接口类型的对象,转换区分进程,客户端服务端位于同一进程,返回服务端的 //Stub对象本身;否则返回的是系统的封装后的Stub.proxy对象。
asBInder
返回Binder对象
onTransact
此方法运行在服务端中的Binder线程池中,当客户端发起跨进程请求时,远程请求会通过系统底层封装后交由此方法处理。
Proxy#add
此方法运行在客户端,当客户端远程调用此方法时,它的内部实现是这样的:首先创建该方法所需要的输入型Parcel对象_data、输出型Parcel对象_reple和返回值对象_result,然后将该方法的参数信息写入_data中;接着调用transact方法来发RPC请求,同时当前线程挂起;然后服务端的onTransact方法会被调用,直到RPC过程返回后,当前线程继续执行,并从_reply中取出RPC过程返回的结果,写入_result中。

2.新建一个客户端File-》new--》new module--》phone & table module。这里我的命名为aidlclient.java
同样要在客户端创建AIDL文件,里面的包名和所在位置要求完全一样。

3.在服务端创建一个Service用来监听客户端的连接请求。

public class IRemoteService extends Service {    @Override  public IBinder onBind(Intent intent) {    return iBinder;  }  private IBinder iBinder = new IImoocAIDL.Stub(){    @Override    public int add(int num1, int num2) throws RemoteException {      Log.e("TAG","收到了来自客户端的请求" + num1 + "+" + num2 );      return num1 + num2;    }  };}

最后,别忘记在AndroidManifest.

<service android:name=".IRemoteService"      android:process=":remote"      android:exported="true">      <intent-filter>        <action android:name="com.mecury.aidltest.IRomoteService"/>      </intent-filter></service>

4.客户端的编写
activity_main.

<?<LinearLayout "http://schemas.android.com/apk/res/android"  "http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical">  <EditText    android:id="@+id/num1"    android:layout_width="match_parent"    android:layout_height="wrap_content" />  <TextView    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:text="+"/>  <EditText    android:id="@+id/num2"    android:layout_width="match_parent"    android:layout_height="wrap_content" />  <TextView    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:text="="/>  <TextView    android:id="@+id/text"    android:layout_width="match_parent"    android:layout_height="30dp" />  <Button    android:id="@+id/button"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:text="计算"/></LinearLayout>

MainActivity.java

package com.mecury.aidlclient;import android.content.ComponentName;import android.content.Context;import android.content.Intent;import android.content.ServiceConnection;import android.os.Bundle;import android.os.IBinder;import android.os.RemoteException;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;import com.mecury.aidltest.IImoocAIDL;public class MainActivity extends AppCompatActivity implements View.OnClickListener {  private EditText num1;  private EditText num2;  private Button button;  private TextView text;  private IImoocAIDL iImoocAIDL;  private ServiceConnection conn = new ServiceConnection() {        @Override    public void onServiceConnected(ComponentName name, IBinder service) {      iImoocAIDL = IImoocAIDL.Stub.asInterface(service);    }    @Override    public void onServiceDisconnected(ComponentName name) {      iImoocAIDL = null;    }  };  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    bindService();    initView();  }  private void initView() {    num1 = (EditText) findViewById(R.id.num1);    num2 = (EditText) findViewById(R.id.num2);    button = (Button) findViewById(R.id.button);    text = (TextView) findViewById(R.id.text);    button.setOnClickListener(this);  }  @Override  public void onClick(View v) {    int num11 = Integer.parseInt(num1.getText().toString());    int num22 = Integer.parseInt(num2.getText().toString());    try {      int res = iImoocAIDL.add(num11,num22);      text.setText(num11 +"+"+ num22 +"="+ res);    } catch (RemoteException e) {      e.printStackTrace();    }  }  private void bindService() {    Intent intent = new Intent();        intent.setAction("com.mecury.aidltest.IRomoteService");        intent.setComponent(new ComponentName("com.mecury.aidltest","com.mecury.aidltest.IRemoteService"));        bindService(intent,conn, Context.BIND_AUTO_CREATE);  }  @Override  protected void onDestroy() {    super.onDestroy();    unbindService(conn);  }}

5.运行代码
先启动服务端,在启动客户端。

结果.gif


小结:看完上面,是不是已经对于AIDL的用法有个大概的了解。下面来看一个更为复杂的例子,这是《android开发艺术探索》中的例子: 建立一个图书管理,能够添加图书、得到图书列表、使用观察者模式、当新书到达时通知所有观察者。

4.AIDL高级示例

1.先看Book.java。需要注意的是,AIDL能够传输的数据类型有限制,这里必须将book序列化才能够使用,同时Book类在客户端和服务端都要这样定义

Book.java
public class Book implements Parcelable {  public int bookId;  public String bookName;  public Book(int bookId, String bookName) {    this.bookId = bookId;    this.bookName = bookName;  }  @Override  public int describeContents() {    return 0;  }  @Override  public void writeToParcel(Parcel dest, int flags) {    dest.writeInt(bookId);    dest.writeString(bookName);  }  protected Book(Parcel in) {    bookId = in.readInt();    bookName = in.readString();  }  public static final Creator<Book> CREATOR = new Creator<Book>() {    @Override    public Book createFromParcel(Parcel in) {      return new Book(in);    }    @Override    public Book[] newArray(int size) {      return new Book[size];    }  };  @Override  public String toString() {    return bookId + ":" + bookName;  }}

2.AIDL文件

Book.aidl
package com.mecury.aidltest2;parcelable Book;
IOnNewBookArrivedListener.aidl
package com.mecury.aidltest2;import com.mecury.aidltest2.book;interface IOnNewBookArrivedListener {   void OnNewBookArrivedListener(in Book book);}
IBookManager.aidl
package com.mecury.aidltest2;import com.mecury.aidltest2.book;import com.mecury.aidltest2.IOnNewBookArrivedListener;interface IBookManager {  List<Book> getBookList();  void addBook(in Book book);  void registerListener(IOnNewBookArrivedListener listener);  void unregisterListener(IOnNewBookArrivedListener listener);}

3.服务端

BookManagerService.java
public class BookManagerService extends Service {  private static final String TAG = "BMS";  private AtomicBoolean mIsServiceDestoryed = new AtomicBoolean(false);  private CopyOnWriteArrayList<Book> mBookList = new CopyOnWriteArrayList<Book>();  private RemoteCallbackList<IOnNewBookArrivedListener> mListeners = new RemoteCallbackList<>();    private Binder mBinder = new IBookManager.Stub(){    @Override    public List<Book> getBookList() throws RemoteException {      return mBookList;    }    @Override    public void addBook(Book book) throws RemoteException {      mBookList.add(book);    }    @Override    public void registerListener(IOnNewBookArrivedListener listener) throws RemoteException {      mListeners.register(listener);    }    @Override    public void unregisterListener(IOnNewBookArrivedListener listener) throws RemoteException {      mListeners.unregister(listener);    }  };  @Override  public void onCreate() {    super.onCreate();    mBookList.add(new Book(1,"Android"));    mBookList.add(new Book(2, "Ios"));    new Thread(new serviceWork()).start();  }  @Nullable  @Override  public IBinder onBind(Intent intent) {    return mBinder;  }    private void onNewBookArrived(Book book) throws RemoteException {    mBookList.add(book);    final int N = mListeners.beginBroadcast();    Log.e("onNewBookArrived","registener listener size:" + N);    for (int i = 0; i < N; i++){      IOnNewBookArrivedListener l = mListeners.getBroadcastItem(i);      if (l!=null){        l.OnNewBookArrivedListener(book);      }    }    mListeners.finishBroadcast();  }    private class serviceWork implements Runnable{    @Override    public void run() {      while (!mIsServiceDestoryed.get()){        try {          Thread.sleep(5000);        } catch (InterruptedException e) {          e.printStackTrace();        }        int bookId = mBookList.size() + 1;        Book newBook = new Book(bookId,"new Book #" + bookId);        try {          onNewBookArrived(newBook);        } catch (RemoteException e) {          e.printStackTrace();        }      }    }  }  @Override  public void onDestroy() {    mIsServiceDestoryed.set(true);    super.onDestroy();  }}
在里面我们发现几处特殊的地方
1.CopyOnWriteArrayList:支持并发的读写,这里我们使用它来进行自动的线程同步
2.RemoteCallBackList:是系统专门提供的用于删除跨进程listener的接口。它的工作原理其实很简单:在它的内部有一个Map结构专门用来保存所有AIDL回调ArrayMap<IBinder, Callback> mCallback = new ArrayMap<IBinder, Callback>();,当客户端注册listener时,会把listener的信息注册到mCallBack中,其中key和value通过下面方式获得:IBinder key = listener.asBinder();Callback value = new Callback(listener, cookie)。另外一点我们需要知道:对 象是不能跨进程传输的,对象的跨进程传输过程实际是反序列化的过程,这是我们Book类为什么要实现Parcelable接口的原因。在跨进程传输 中,Binder会把客户端传递的对象重新转化并生成另一对象,当我们注册和解注册的过程中使用的是同一个客户端对象,但是通过Binder传递到服务端 却生成了两个不同的对象。而RemoteCallBackList就是用来解决这个问题的,虽然所多次跨进程传输客户端的同一个对象会在服务端 生成不同的对象,但在这些新生成的对象都有一个共同点,那就是他们底层的Binder对象是同一个,利用这个,就可以实现上面无法实现的功能。当客户端解 注册时,我们只要遍历所有的listener,找出那个和解注册listener具有相同Binder对象服务器listener并把他删除掉即可,这就 是RemoteCallbackList为我们做的事情。(对于这个看不明白的,可以看看《android 开发艺术探索》)

4.客户端:

MainActivity.java
public class MainActivity extends AppCompatActivity {  private static final String TAG = "BookManagerActivity";  private IBookManager bookManager;  private static final int MESSAGE_NEW_BOOK_ARRIVED = 1;  private Handler mHandler = new Handler(){    @Override    public void handleMessage(Message msg) {      switch (msg.what){        case MESSAGE_NEW_BOOK_ARRIVED:          Log.e(TAG, "received new book:" + msg.obj);          break;        default:          super.handleMessage(msg);      }    }  };  private ServiceConnection mService = new ServiceConnection() {    @Override    public void onServiceConnected(ComponentName name, IBinder service) {      bookManager = IBookManager.Stub.asInterface(service);      try {        List<Book> list = bookManager.getBookList();        Log.e(TAG, "query book list,list type:" + list.getClass().getCanonicalName());        Log.e(TAG, "query book list:" + list.toString());        Book newBook = new Book(3, "android进阶");        bookManager.addBook(newBook);        Log.e(TAG, "add book:" + newBook);        List<Book> newList = bookManager.getBookList();        Log.e(TAG, "query book list:" + newList.toString());        bookManager.registerListener(mNewBookArrivedListener);      } catch (RemoteException e) {        e.printStackTrace();      }    }    @Override    public void onServiceDisconnected(ComponentName name) {      bookManager = null;      Log.e(TAG, "binder died.");    }  };  private IOnNewBookArrivedListener mNewBookArrivedListener = new IOnNewBookArrivedListener.Stub() {    @Override    public void OnNewBookArrivedListener(Book book) throws RemoteException {      mHandler.obtainMessage(MESSAGE_NEW_BOOK_ARRIVED, book).sendToTarget();    }  };  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    bindService();  }  private void bindService() {    Intent intent = new Intent();    intent.setAction("com.mecury.aidltest2.BookManagerService");    intent.setComponent(new ComponentName("com.mecury.aidltest2", "com.mecury.aidltest2.BookManagerService"));    bindService(intent, mService, Context.BIND_AUTO_CREATE);  }  @Override  protected void onDestroy() {    if (bookManager != null && bookManager.asBinder().isBinderAlive()){      Log.e(TAG, "unregister listener:" + mNewBookArrivedListener);      try {        bookManager.unregisterListener(mNewBookArrivedListener);      } catch (RemoteException e) {        e.printStackTrace();      }    }    unbindService(mService);    super.onDestroy();  }}

目录结构:


目录


运行结果:

客户端log:

06-29 22:52:29.438 17007-17007/com.mecury.client E/BookManagerActivity: query book list,list type:java.util.ArrayList06-29 22:52:29.438 17007-17007/com.mecury.client E/BookManagerActivity: query book list:[1:Android, 2:Ios]06-29 22:52:29.439 17007-17007/com.mecury.client E/BookManagerActivity: add book:3:android进阶06-29 22:52:29.439 17007-17007/com.mecury.client E/BookManagerActivity: query book list:[1:Android, 2:Ios, 3:android进阶]06-29 22:52:33.487 17007-17007/com.mecury.client E/BookManagerActivity: received new book:4:new Book #406-29 22:52:38.489 17007-17007/com.mecury.client E/BookManagerActivity: received new book:5:new Book #506-29 22:52:43.491 17007-17007/com.mecury.client E/BookManagerActivity: received new book:6:new Book #606-29 22:52:48.503 17007-17007/com.mecury.client E/BookManagerActivity: received new book:7:new Book #7

服务端log:

06-29 22:52:33.487 17027-17044/com.mecury.aidltest2:remote E/onNewBookArrived: registener listener size:106-29 22:52:38.488 17027-17044/com.mecury.aidltest2:remote E/onNewBookArrived: registener listener size:106-29 22:52:43.490 17027-17044/com.mecury.aidltest2:remote E/onNewBookArrived: registener listener size:106-29 22:52:48.492 17027-17044/com.mecury.aidltest2:remote E/onNewBookArrived: registener listener size:1

5.一些补充

AIDL支持的数据类型
  • 基本数据类型(int、long、char 等)
  • String 和 CharSequence
  • List:只支持ArrayList,里面的每个元素都必须被AIDL支持。
  • Map: 只支持HashMap, 里面的每个元素都必须被AIDL支持。
  • Parcelable: 所有实现了Parcelable接口的对象
  • AIDL: 所有的AIDL接口本身也可以在AIDL文件中使用

参考:
1.《android开发艺术探索》