Android进程间通信之AIDL工作原理初探
【摘要】 我们新建了AIDL文件后，再build一下项目，就会生成编译后的AIDL，如：
// IMyAidlInterface.aidl
package com.wong.remoteservice;
// Declare any non-default types here with import statements
interface IMyAidlInterface ...
我们新建了AIDL文件后，再build一下项目，就会生成编译后的AIDL，如：
// IMyAidlInterface.aidl
package com.wong.remoteservice;
// Declare any non-default types here with import statements
interface IMyAidlInterface { // 服务端数据 String getString();
}
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编译后得到的 IMyAidlInterface.java:
/*
* This file is auto-generated. DO NOT MODIFY.
*/
package com.wong.remoteservice;
// Declare any non-default types here with import statements
public interface IMyAidlInterface extends android.os.IInterface
{
/** Default implementation for IMyAidlInterface. */
public static class Default implements com.wong.remoteservice.IMyAidlInterface
{ // 服务端数据 @Override public java.lang.String getString() throws android.os.RemoteException { return null; } @Override public android.os.IBinder asBinder() { return null; }
}
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.wong.remoteservice.IMyAidlInterface
{ private static final java.lang.String DESCRIPTOR = "com.wong.remoteservice.IMyAidlInterface"; /** Construct the stub at attach it to the interface. */ public Stub() { this.attachInterface(this, DESCRIPTOR); } /** * Cast an IBinder object into an com.wong.remoteservice.IMyAidlInterface interface, * generating a proxy if needed. */ public static com.wong.remoteservice.IMyAidlInterface asInterface(android.os.IBinder obj) { if ((obj==null)) { return null; } android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR); if (((iin!=null)&&(iin instanceof com.wong.remoteservice.IMyAidlInterface))) { return ((com.wong.remoteservice.IMyAidlInterface)iin); } return new com.wong.remoteservice.IMyAidlInterface.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_getString: { data.enforceInterface(descriptor); java.lang.String _result = this.getString(); reply.writeNoException(); reply.writeString(_result); return true; } default: { return super.onTransact(code, data, reply, flags); } } } private static class Proxy implements com.wong.remoteservice.IMyAidlInterface { 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; } // 服务端数据 @Override public java.lang.String getString() throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); java.lang.String _result; try { _data.writeInterfaceToken(DESCRIPTOR); boolean _status = mRemote.transact(Stub.TRANSACTION_getString, _data, _reply, 0); if (!_status && getDefaultImpl() != null) { return getDefaultImpl().getString(); } _reply.readException(); _result = _reply.readString(); } finally { _reply.recycle(); _data.recycle(); } return _result; } public static com.wong.remoteservice.IMyAidlInterface sDefaultImpl; } static final int TRANSACTION_getString = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0); public static boolean setDefaultImpl(com.wong.remoteservice.IMyAidlInterface impl) { if (Stub.Proxy.sDefaultImpl == null && impl != null) { Stub.Proxy.sDefaultImpl = impl; return true; } return false; } public static com.wong.remoteservice.IMyAidlInterface getDefaultImpl() { return Stub.Proxy.sDefaultImpl; }
}
// 服务端数据 public java.lang.String getString() throws android.os.RemoteException;
}
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我们来仔细分析一下，这个编译后的AIDL。整体结构是这样的：
IMyAidlInterface继承了IInterface接口，IInterface接口：
IBinder是用于远程对象的基础接口。轻量级远程调用机制的核心部分，为提高在进程内和跨进程调用的性能而设计。 这个接口描述了与远程对象交互使用的抽象协议，不要直接实现这个接口，而是通过继承Binder来完成。在Android中，实现远程对象（服务）的调用，就是靠Binder来实现的。
（1）Default类，提供了默认实现。
（2）我们自己定义的接口getString，这个接口要在服务端实现，最终也是通过这个接口向外提供服务的。
（3）为了获得实现了getString接口的对象，我们现在要介绍最重要的Ｓtub类：
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.wong.remoteservice.IMyAidlInterface
{ private static final java.lang.String DESCRIPTOR = "com.wong.remoteservice.IMyAidlInterface"; /** Construct the stub at attach it to the interface. */ public Stub() { this.attachInterface(this, DESCRIPTOR); } /** * Cast an IBinder object into an com.wong.remoteservice.IMyAidlInterface interface, * generating a proxy if needed. */ public static com.wong.remoteservice.IMyAidlInterface asInterface(android.os.IBinder obj) { if ((obj==null)) { return null; } android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR); if (((iin!=null)&&(iin instanceof com.wong.remoteservice.IMyAidlInterface))) { return ((com.wong.remoteservice.IMyAidlInterface)iin); } return new com.wong.remoteservice.IMyAidlInterface.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_getString: { data.enforceInterface(descriptor); java.lang.String _result = this.getString(); reply.writeNoException(); reply.writeString(_result); return true; } default: { return super.onTransact(code, data, reply, flags); } } } private static class Proxy implements com.wong.remoteservice.IMyAidlInterface { 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; } // 服务端数据 @Override public java.lang.String getString() throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); java.lang.String _result; try { _data.writeInterfaceToken(DESCRIPTOR); boolean _status = mRemote.transact(Stub.TRANSACTION_getString, _data, _reply, 0); if (!_status && getDefaultImpl() != null) { return getDefaultImpl().getString(); } _reply.readException(); _result = _reply.readString(); } finally { _reply.recycle(); _data.recycle(); } return _result; } public static com.wong.remoteservice.IMyAidlInterface sDefaultImpl; } static final int TRANSACTION_getString = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0); public static boolean setDefaultImpl(com.wong.remoteservice.IMyAidlInterface impl) { if (Stub.Proxy.sDefaultImpl == null && impl != null) { Stub.Proxy.sDefaultImpl = impl; return true; } return false; } public static com.wong.remoteservice.IMyAidlInterface getDefaultImpl() { return Stub.Proxy.sDefaultImpl; }
}
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Stub的结构如下：
- Stub类是一个抽象类实现了IMyAidlInterface接口，但Stub并不实现getString这个方法，留给真正要对外服务的子类来实现。
- Stub类继承了Binder，使得Stub具有访问远程对象的能力。
- asInterface接口：
在客户端获取服务端的数据是这样获得的：
private IMyAidlInterface myBind;
private ServiceConnection serviceConnection = new ServiceConnection() { @Override public void onServiceConnected(ComponentName name, IBinder service) { myBind = IMyAidlInterface.Stub.asInterface(service); } @Override public void onServiceDisconnected(ComponentName name) { } };
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由调用方式IMyAidlInterface.Stub.asInterface(service)可知，Stub没有被初始化，因此执行了：
return new com.wong.remoteservice.IMyAidlInterface.Stub.Proxy(obj);
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返回了一个代理Proxy对象，那么我们看看定义在Stub类里的内部类Proxy：
private static class Proxy implements com.wong.remoteservice.IMyAidlInterface { 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; } // 服务端数据 @Override public java.lang.String getString() throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); java.lang.String _result; try { _data.writeInterfaceToken(DESCRIPTOR); boolean _status = mRemote.transact(Stub.TRANSACTION_getString, _data, _reply, 0); if (!_status && getDefaultImpl() != null) { return getDefaultImpl().getString(); } _reply.readException(); _result = _reply.readString(); } finally { _reply.recycle(); _data.recycle(); } return _result; } public static com.wong.remoteservice.IMyAidlInterface sDefaultImpl; }
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从这个代理可知，当我们要调用getString方法获得服务器数据时，它就会通过Binder对象的transact，向服务端请求数据。通过这种方式来完成跨进程的通信。
boolean _status = mRemote.transact(Stub.TRANSACTION_getString, _data, _reply, 0);
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以上就是关于AIDL的通信原理的一部分知识。
谢谢阅读
文章来源: blog.csdn.net，作者：WongKyunban，版权归原作者所有，如需转载，请联系作者。
原文链接：blog.csdn.net/weixin_40763897/article/details/103867859
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