android进程间通信机制之AIDL原理解读-Android-IT72.COM

android进程间通信机制之AIDL原理解读

Home / Android MrLee 2015-5-29 3358

aidl是怎样可以做到进程间通信的，它的执行过程是怎样的？这篇文章来分析IRemoteService.aidl的执行过程，并理解aidl是怎样跨进程通信的。当我们创建IRemoteService.aidl文件时，IDE会为我们在gen目录中创建相应的文件。

/** This file is auto-generated.  DO NOT MODIFY.  
 * Original file: F:\\workspace\\AndroidImprove\\src\\com\\example\\aidl\\IRemoteService.aidl  
 */  
package com.example.aidl;  
public interface IRemoteService extends android.os.IInterface  
{  
/** Local-side IPC implementation stub class. */  
public static abstract class Stub extends android.os.Binder implements com.example.aidl.IRemoteService  
{  
private static final java.lang.String DESCRIPTOR = "com.example.aidl.IRemoteService";  
/** Construct the stub at attach it to the interface. */  
public Stub()  
{  
this.attachInterface(this, DESCRIPTOR);  
}  
/**  
 * Cast an IBinder object into an com.example.aidl.IRemoteService interface,  
 * generating a proxy if needed.  
 */  
public static com.example.aidl.IRemoteService asInterface(android.os.IBinder obj)  
{  
if ((obj==null)) {  
return null;  
}  
android.os.IInterface iin = (android.os.IInterface)obj.queryLocalInterface(DESCRIPTOR);  
if (((iin!=null)&&(iin instanceof com.example.aidl.IRemoteService))) {  
return ((com.example.aidl.IRemoteService)iin);  
}  
return new com.example.aidl.IRemoteService.Stub.Proxy(obj);  
}  
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_register:  
{  
data.enforceInterface(DESCRIPTOR);  
com.example.aidl.IRemoteCallback _arg0;  
_arg0 = com.example.aidl.IRemoteCallback.Stub.asInterface(data.readStrongBinder());  
this.register(_arg0);  
reply.writeNoException();  
return true;  
}  
case TRANSACTION_unregister:  
{  
data.enforceInterface(DESCRIPTOR);  
com.example.aidl.IRemoteCallback _arg0;  
_arg0 = com.example.aidl.IRemoteCallback.Stub.asInterface(data.readStrongBinder());  
this.unregister(_arg0);  
reply.writeNoException();  
return true;  
}  
case TRANSACTION_execute:  
{  
data.enforceInterface(DESCRIPTOR);  
this.execute();  
reply.writeNoException();  
return true;  
}  
case TRANSACTION_getStatus:  
{  
data.enforceInterface(DESCRIPTOR);  
java.lang.String _arg0;  
_arg0 = data.readString();  
int _result = this.getStatus(_arg0);  
reply.writeNoException();  
reply.writeInt(_result);  
return true;  
}  
}  
return super.onTransact(code, data, reply, flags);  
}  
private static class Proxy implements com.example.aidl.IRemoteService  
{  
private android.os.IBinder mRemote;  
Proxy(android.os.IBinder remote)  
{  
mRemote = remote;  
}  
public android.os.IBinder asBinder()  
{  
return mRemote;  
}  
public java.lang.String getInterfaceDescriptor()  
{  
return DESCRIPTOR;  
}  
//注册回调  
  
public void register(com.example.aidl.IRemoteCallback callback) throws android.os.RemoteException  
{  
android.os.Parcel _data = android.os.Parcel.obtain();  
android.os.Parcel _reply = android.os.Parcel.obtain();  
try {  
_data.writeInterfaceToken(DESCRIPTOR);  
_data.writeStrongBinder((((callback!=null))?(callback.asBinder()):(null)));  
mRemote.transact(Stub.TRANSACTION_register, _data, _reply, 0);  
_reply.readException();  
}  
finally {  
_reply.recycle();  
_data.recycle();  
}  
}  
//取消注册回调  
  
public void unregister(com.example.aidl.IRemoteCallback callback) throws android.os.RemoteException  
{  
android.os.Parcel _data = android.os.Parcel.obtain();  
android.os.Parcel _reply = android.os.Parcel.obtain();  
try {  
_data.writeInterfaceToken(DESCRIPTOR);  
_data.writeStrongBinder((((callback!=null))?(callback.asBinder()):(null)));  
mRemote.transact(Stub.TRANSACTION_unregister, _data, _reply, 0);  
_reply.readException();  
}  
finally {  
_reply.recycle();  
_data.recycle();  
}  
}  
//执行回调  
  
public void execute() throws android.os.RemoteException  
{  
android.os.Parcel _data = android.os.Parcel.obtain();  
android.os.Parcel _reply = android.os.Parcel.obtain();  
try {  
_data.writeInterfaceToken(DESCRIPTOR);  
mRemote.transact(Stub.TRANSACTION_execute, _data, _reply, 0);  
_reply.readException();  
}  
finally {  
_reply.recycle();  
_data.recycle();  
}  
}  
//获取状态  
  
public int getStatus(java.lang.String flag) 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.writeString(flag);  
mRemote.transact(Stub.TRANSACTION_getStatus, _data, _reply, 0);  
_reply.readException();  
_result = _reply.readInt();  
}  
finally {  
_reply.recycle();  
_data.recycle();  
}  
return _result;  
}  
}  
static final int TRANSACTION_register = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);  
static final int TRANSACTION_unregister = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);  
static final int TRANSACTION_execute = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2);  
static final int TRANSACTION_getStatus = (android.os.IBinder.FIRST_CALL_TRANSACTION + 3);  
}  
//注册回调  
  
public void register(com.example.aidl.IRemoteCallback callback) throws android.os.RemoteException;  
//取消注册回调  
  
public void unregister(com.example.aidl.IRemoteCallback callback) throws android.os.RemoteException;  
//执行回调  
  
public void execute() throws android.os.RemoteException;  
//获取状态  
  
public int getStatus(java.lang.String flag) throws android.os.RemoteException;  
}

在ClientActivity绑定远程Service并建立连接时会调用ServiceConnection.onServiceConnected(ComponentName name, IBinder service)

public void onServiceConnected(ComponentName name, IBinder service) {  
            remoteService = IRemoteService.Stub.asInterface(service);  
            //注册回调  
            try {  
                remoteService.register(remoteCallback);  
            } catch (RemoteException e) {  
                e.printStackTrace();  
            }  
}

IBinder service是从RemoteService返回的IRemoteService.Stub iBinder，这个对象是Server应用进程中的对象。 IRemoteService.Stub.asInterface(service)在本地创建了一个代理
public static com.example.aidl.IRemoteService asInterface(android.os.IBinder obj) { if ((obj==null)) { return null; } android.os.IInterface iin = (android.os.IInterface)obj.queryLocalInterface(DESCRIPTOR);//这里肯定返回null if (((iin!=null)&&(iin instanceof com.example.aidl.IRemoteService))) { return ((com.example.aidl.IRemoteService)iin); } return new com.example.aidl.IRemoteService.Stub.Proxy(obj);//创建一个本地代理 }
当使用remoteService调用方法时，其实是调用了本地com.example.aidl.IRemoteService.Stub.Proxy对象的方法，从Proxy方法中可以看到，每个方法都执行了mRemote.transact(Stub.TRANSACTION_xxx, _data, _reply, 0);。如：

//获取状态  
  
public int getStatus(java.lang.String flag) 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.writeString(flag);  
mRemote.transact(Stub.TRANSACTION_getStatus, _data, _reply, 0);  
_reply.readException();  
_result = _reply.readInt();  
}  
finally {  
_reply.recycle();  
_data.recycle();  
}  
return _result;  
}

这一过程是把Client端的参数转换成Parcel（_data）传递到Server端，而在Server端又会把返回数据保存到_reply中，这就形成了一次交互。 mRemote是远程对象，transact方法会执行onTransact方法

public final boolean transact(int code, Parcel data, Parcel reply,  
            int flags) throws RemoteException {  
        if (Config.LOGV) Log.v("Binder", "Transact: " + code + " to " + this);  
        if (data != null) {  
            data.setDataPosition(0);  
        }  
        boolean r = onTransact(code, data, reply, flags);  
        if (reply != null) {  
            reply.setDataPosition(0);  
        }  
        return r;  
    }

这样就会执行远程的onTransact方法，

case TRANSACTION_getStatus:  
{  
data.enforceInterface(DESCRIPTOR);  
java.lang.String _arg0;  
_arg0 = data.readString();  
int _result = this.getStatus(_arg0);  
reply.writeNoException();  
reply.writeInt(_result);  
return true;  
}

注意 int _result = this.getStatus(_arg0);，这就调用了Server端的getStatus(String flag)，并把返回结果写到Client端的代理Proxy对象的_reply中.
到此，aidl通信过程就完成了。

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