Android开发接口描述.doc

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1、接口描述语言（AIDL）译者署名： 移动云_文斌译者链接：版本：Android 2.3 r1原文 (注意：3.0 r1 以后移到Appendix下)使用AIDL设计远程接口(Designing a Remote Interface Using AIDL)由于每个应用程序都运行在自己的进程空间，并且可以从应用程序UI运行另一个服务进程，而且经常会在不同的进程间传递对象。在Android平台，一个进程通常不能访问另一个进程的内存空间，所以要想对话，需要将对象分解成操作系统可以理解的基本单元，并且有序的通过进程边界。通过代码来实现这个数据传输过程是冗长乏味的，Android提供了AIDL工具来处理这

2、项工作。AIDL (Android Interface Definition Language)是一种IDL 语言，用于生成可以在Android设备上两个进程之间进行进程间通信(IPC)的代码。如果在一个进程中（例如Activity）要调用另一个进程中（例如Service）对象的操作，就可以使用AIDL生成可序列化的参数。AIDL IPC机制是面向接口的，像COM或Corba一样，但是更加轻量级。它是使用代理类在客户端和实现端传递数据。使用AIDL实现IPC(Implementing IPC Using AIDL)使用AIDL实现IPC服务的步骤是：1. 创建.aidl文件-该文件（YourI

3、nterface.aidl）定义了客户端可用的方法和数据的接口。2. 在makefile文件中加入.aidl文件-（Eclipse中的ADT插件提供管理功能）Android包括名为AIDL的编译器，位于tools/文件夹。3. 实现接口-AIDL编译器从AIDL接口文件中利用Java语言创建接口，该接口有一个继承的命名为Stub的内部抽象类（并且实现了一些IPC调用的附加方法），要做的就是创建一个继承于YourInterface.Stub的类并且实现在.aidl文件中声明的方法。4. 向客户端公开接口-如果是编写服务，应该继承Service并且重载Service.onBind(Intent)

4、以返回实现了接口的对象实例创建.aidl文件(Create an .aidl File)AIDL使用简单的语法来声明接口，描述其方法以及方法的参数和返回值。这些参数和返回值可以是任何类型，甚至是其他AIDL生成的接口。重要的是必须导入所有非内置类型，哪怕是这些类型是在与接口相同的包中。下面是AIDL能支持的数据类型：l Java编程语言的主要类型 (int, boolean等) 不需要 import 语句。l 以下的类 (不需要import 语句):n Stringn List -列表中的所有元素必须是在此列出的类型，包括其他AIDL生成的接口和可打包类型。List可以像一般的类（例如List

5、）那样使用，另一边接收的具体类一般是一个ArrayList，这些方法会使用List接口。n Map - Map中的所有元素必须是在此列出的类型，包括其他AIDL生成的接口和可打包类型。一般的maps（例如Map）不被支持，另一边接收的具体类一般是一个HashMap，这些方法会使用Map接口。n CharSequence -该类是被TextView和其他控件对象使用的字符序列。l 通常引引用方式传递的其他AIDL生成的接口，必须要import 语句声明l 实现了Parcelable protocol 以及按值传递的自定义类，必须要import 语句声明。以下是基本的AIDL语法：实现接口(Imp

6、lementing the Interface)/My AIDL file,named SomeCloss.aidl/Note that standard comment syntax is respected./Comments before the import or package statements are not bubbled up/to the generated interface,but comments above interface/method/field/declarations are added to the generated interface./Inclu

7、de your fully-qualified package statement.Package com.android.sample;/See the list above for which classes need/import statements(hintmost of them)Import com.android.sample .IAtmService;/Declare the interface.iterface IBankAccountService /Methods can take 0 or more parameters, and/return a value or

8、void.int getAccountBalance();void setOwnerNames(in List names);/Methods can even take other AIDL-defined parameters.BankAccount createAccount(in String name, int startingDeposit, in IAtmService atmService);/All non-Java primitive parameters(e.g., int, bool, etc) require;/ a directional tag indicatin

9、g which way the data will go. Available/ values are in, out, inout. (Primitives are in by default, and cannot be otherwise)./ Limit the direction to what is truly needed, because marshalling parameters/ is expensive.int getCustomerList(in String branch, out String customerList); AIDL生成了与.aidl文件同名的接口

10、，如果使用Eclipse插件，AIDL会做为编译过程的一部分自动运行（不需要先运行AIDL再编译项目），如果没有插件，就要先运行AIDL。 生成的接口包含一个名为Stub的抽象的内部类，该类声明了所有.aidl中描述的方法，Stub还定义了少量的辅助方法，尤其是asInterface()，通过它或以获得IBinder（当applicationContext.bindService()成功调用时传递到客户端的onServiceConnected()）并且返回用于调用IPC方法的接口实例，更多细节参见Calling an IPC Method。 要实现自己的接口，就从YourInterface.S

11、tub类继承，然后实现相关的方法（可以创建.aidl文件然后实现stub方法而不用在中间编译，Android编译过程会在.java文件之前处理.aidl文件）。 这个例子实现了对IRemoteService接口的调用，这里使用了匿名对象并且只有一个getPid()接口。/ No need to import IRemoteService if its in the same project.private final IRemoteService.Stub mBinder = new IRemoteService.Stub()public int getPid()return Process.

12、myPid(); 这里是实现接口的几条说明：l 不会有返回给调用方的异常l 默认IPC调用是同步的。如果已知IPC服务端会花费很多毫秒才能完成，那就不要在Activity或View线程中调用，否则会引起应用程序挂起（Android可能会显示“应用程序未响应”对话框），可以试着在独立的线程中调用。l AIDL接口中只支持方法，不能声明静态成员。向客户端暴露接口(Exposing Your Interface to Clients) 在完成了接口的实现后需要向客户端暴露接口了，也就是发布服务，实现的方法是继承 Service，然后实现以Service.onBind(Intent)返回一个实现了接口

13、的类对象。下面的代码片断表示了暴露IRemoteService接口给客户端的方式。public class RemoteService extends Service .Override public IBinder onBind(Intent intent) / Select the interface to return. If your service only implements / a single interface, you can just return it here without checking / the Intent. if (IRemoteService.cla

14、ss.getName().equals(intent.getAction() return mBinder; if (ISecondary.class.getName().equals(intent.getAction() return mSecondaryBinder; return null; /* * The IRemoteInterface is defined through IDL */ private final IRemoteService.Stub mBinder = new IRemoteService.Stub() public void registerCallback

15、(IRemoteServiceCallback cb) if (cb != null) mCallbacks.register(cb); public void unregisterCallback(IRemoteServiceCallback cb) if (cb != null) mCallbacks.unregister(cb); ; /* * A secondary interface to the service. */ private final ISecondary.Stub mSecondaryBinder = new ISecondary.Stub() public int

16、getPid() return Process.myPid(); public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, String aString) ;使用可打包接口传递参数Pass by value Parameters using Parcelables如果有类想要能过AIDL在进程之间传递，这一想法是可以实现的，必须确保这个类在IPC的两端的有效性，通常的情形是与一个启动的服务通信。这里列出了使类能够支持Parcelable的4个步骤：【译者注：原文为5

17、，但列表为4项，疑为作者笔误】1. 使该类实现Parcelabel接口。2. 实现public void writeToParcel(Parcel out) 方法，以便可以将对象的当前状态写入包装对象中。3. 增加名为CREATOR的构造器到类中，并实现Parcelable.Creator接口。4. 最后，但同样重要的是，创建AIDL文件声明这个可打包的类（见下文），如果使用的是自定义的编译过程，那么不要编译此AIDL文件，它像C语言的头文件一样不需要编译。AIDL会使用这些方法的成员序列化和反序列化对象。这个例子演示了如何让Rect类实现Parcelable接口。import android

18、.os.Parcel;import android.os.Parcelable;public final class Rect implements Parcelable public int left;public int top;public int right;public int bottom;public static final Parcelable.Creator CREATOR = new Parcelable.Creator() public Rect createFromParcel(Parcel in) return new Rect(in); public Rect n

19、ewArray(int size) return new Rectsize; ;public Rect() private Rect(Parcel in) readFromParcel(in);public void writeToParcel(Parcel out) out.writeInt(left); out.writeInt(top); out.writeInt(right); out.writeInt(bottom);public void readFromParcel(Parcel in) left = in.readInt(); top = in.readInt(); right

20、 = in.readInt(); bottom = in.readInt(); 这个是Rect.aidl文件。package android.graphics;/ Declare Rect so AIDL can find it and knows that it implements/ the parcelable protocol.Parcelable Rect;序列化Rect类的工作相当简单，对可打包的其他类型的数据可以参见Parcel类。警告：不要忘了对从其他进程接收到的数据进行安全检查。在上面的例子中，rect要从数据包中读取4个数值，需要确认无论调用方想要做什么，这些数值都是在可接

21、受的范围之内。想要了解更多的关于保持应用程序安全的内容，可参见 Security and Permissions。调用IPC方法(Calling an IPC Method)这里给出了调用远端接口的步骤：1. 声明.aidl文件中定义的接口类型的变量。2. 实现ServiceConnection3. 调用Context.bindService()，传递ServiceConnection的实现4. 在ServiceConnection.onServiceConnected()方法中会接收到IBinder对象，调用YourInterfaceName.Stub.asInterface(IBinder

22、)service)将返回值转换为YourInterface类型5. 调用接口中定义的方法。应该总是捕获连接被打断时抛出的DeadObjectException异常，这是远端方法唯一的异常。6. 调用Context.unbindService()断开连接这里是几个调用IPC服务的提示：l 对象是在进程间进行引用计数l 可以发送匿名对象作为方法参数 以下是演示调用AIDL创建的服务，可以在ApiDemos项目中获取远程服务的示例。public static class Binding extends Activity /* The primary interface we will be call

23、ing on the service. */IRemoteService mService = null;/* Another interface we use on the service. */ISecondary mSecondaryService = null;Button mKillButton;TextView mCallbackText;private boolean mIsBound;/* Standard initialization of this activity. Set up the UI, then wait* for the user to poke it bef

24、ore doing anything.*/Overrideprotected void onCreate(Bundle savedInstanceState) super.onCreate(savedInstanceState); setContentView(R.layout.remote_service_binding); / Watch for button clicks. Button button = (Button)findViewById(R.id.bind); button.setOnClickListener(mBindListener); button = (Button)

25、findViewById(R.id.unbind); button.setOnClickListener(mUnbindListener); mKillButton = (Button)findViewById(R.id.kill); mKillButton.setOnClickListener(mKillListener); mKillButton.setEnabled(false); mCallbackText = (TextView)findViewById(R.id.callback); mCallbackText.setText(Not attached.);/* * Class f

26、or interacting with the main interface of the service. */private ServiceConnection mConnection = new ServiceConnection() public void onServiceConnected(ComponentName className, IBinder service) / This is called when the connection with the service has been / established, giving us the service object

27、 we can use to / interact with the service. We are communicating with our / service through an IDL interface, so get a client-side / representation of that from the raw service object. mService = IRemoteService.Stub.asInterface(service); mKillButton.setEnabled(true); mCallbackText.setText(Attached.)

28、; / We want to monitor the service for as long as we are / connected to it. try mService.registerCallback(mCallback); catch (RemoteException e) / In this case the service has crashed before we could even / do anything with it; we can count on soon being / disconnected (and then reconnected if it can

29、 be restarted) / so there is no need to do anything here. / As part of the sample, tell the user what happened. Toast.makeText(Binding.this, R.string.remote_service_connected, Toast.LENGTH_SHORT).show(); public void onServiceDisconnected(ComponentName className) / This is called when the connection

30、with the service has been / unexpectedly disconnected - that is, its process crashed. mService = null; mKillButton.setEnabled(false); mCallbackText.setText(Disconnected.); / As part of the sample, tell the user what happened. Toast.makeText(Binding.this, R.string.remote_service_disconnected, Toast.L

31、ENGTH_SHORT).show(); ;/* * Class for interacting with the secondary interface of the service. */private ServiceConnection mSecondaryConnection = new ServiceConnection() public void onServiceConnected(ComponentName className, IBinder service) / Connecting to a secondary interface is the same as any /

32、 other interface. mSecondaryService = ISecondary.Stub.asInterface(service); mKillButton.setEnabled(true); public void onServiceDisconnected(ComponentName className) mSecondaryService = null; mKillButton.setEnabled(false); ;private OnClickListener mBindListener = new OnClickListener() public void onC

33、lick(View v) / Establish a couple connections with the service, binding / by interface names. This allows other applications to be / installed that replace the remote service by implementing / the same interface. bindService(new Intent(IRemoteService.class.getName(), mConnection, Context.BIND_AUTO_C

34、REATE); bindService(new Intent(ISecondary.class.getName(), mSecondaryConnection, Context.BIND_AUTO_CREATE); mIsBound = true; mCallbackText.setText(Binding.); ;private OnClickListener mUnbindListener = new OnClickListener() public void onClick(View v) if (mIsBound) / If we have received the service,

35、and hence registered with / it, then now is the time to unregister. if (mService != null) try mService.unregisterCallback(mCallback); catch (RemoteException e) / There is nothing special we need to do if the service / has crashed. / Detach our existing connection. unbindService(mConnection); unbindS

36、ervice(mSecondaryConnection); mKillButton.setEnabled(false); mIsBound = false; mCallbackText.setText(Unbinding.); ;private OnClickListener mKillListener = new OnClickListener() public void onClick(View v) / To kill the process hosting our service, we need to know its / PID. Conveniently our service

37、has a call that will return / to us that information. if (mSecondaryService != null) try int pid = mSecondaryService.getPid(); / Note that, though this API allows us to request to / kill any process based on its PID, the kernel will / still impose standard restrictions on which PIDs you / are actual

38、ly able to kill. Typically this means only / the process running your application and any additional / processes created by that app as shown here; packages / sharing a common UID will also be able to kill each / others processes. Process.killProcess(pid); mCallbackText.setText(Killed service proces

39、s.); catch (RemoteException ex) / Recover gracefully from the process hosting the / server dying. / Just for purposes of the sample, put up a notification. Toast.makeText(Binding.this, R.string.remote_call_failed, Toast.LENGTH_SHORT).show(); ;/ -/ Code showing how to deal with callbacks./ -/* * This

40、 implementation is used to receive callbacks from the remote * service.*/private IRemoteServiceCallback mCallback = new IRemoteServiceCallback.Stub() /* * This is called by the remote service regularly to tell us about * new values. Note that IPC calls are dispatched through a thread * pool running in each process, so the code executing here will * NOT be running in our main thread like most other things - so, * to update the UI, we need to us