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:
- 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。
- 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。
- 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。
- 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。
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.aidl
package com.mecury.aidltest;
// Declare any non-default types here with import statements
interface 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。
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.xml中注册该Service。
<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.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="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。
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:
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.ArrayList
06-29 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 #4
06-29 22:52:38.489 17007-17007/com.mecury.client E/BookManagerActivity: received new book:5:new Book #5
06-29 22:52:43.491 17007-17007/com.mecury.client E/BookManagerActivity: received new book:6:new Book #6
06-29 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:1
06-29 22:52:38.488 17027-17044/com.mecury.aidltest2:remote E/onNewBookArrived: registener listener size:1
06-29 22:52:43.490 17027-17044/com.mecury.aidltest2:remote E/onNewBookArrived: registener listener size:1
06-29 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》