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android AIDL IPC深入分析

發布時間：2023/11/27 生活经验 42 豆豆

生活随笔收集整理的這篇文章主要介紹了 android AIDL IPC深入分析小編覺得挺不錯的,現在分享給大家,幫大家做個參考.

深入分析AIDL原理

博客分類：
Android

在上一篇文章（Service使用方式）中，介紹了Android進程間通信（IPC）的使用，并給出了一個示例。但并沒有深入分析aidl是怎樣可以做到進程間通信的，它的執行過程是怎樣的？

這篇文章來分析IRemoteService.aidl的執行過程，并理解aidl是怎樣跨進程通信的。

當我們創建IRemoteService.aidl文件時，IDE會為我們在gen目錄中創建相應的文件。

Iremoteservice.java代碼 ?

/**?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;??
}??
//注冊回調??
??
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();??
}??
}??
//取消注冊回調??
??
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();??
}??
}??
//執行回調??
??
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();??
}??
}??
//獲取狀態??
??
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);??
}??
//注冊回調??
??
public?void?register(com.example.aidl.IRemoteCallback?callback)?throws?android.os.RemoteException;??
//取消注冊回調??
??
public?void?unregister(com.example.aidl.IRemoteCallback?callback)?throws?android.os.RemoteException;??
//執行回調??
??
public?void?execute()?throws?android.os.RemoteException;??
//獲取狀態??
??
public?int?getStatus(java.lang.String?flag)?throws?android.os.RemoteException;??
}??

在ClientActivity綁定遠程Service并建立連接時會調用ServiceConnection.onServiceConnected(ComponentName name, IBinder service)

Java代碼 ?

public?void?onServiceConnected(ComponentName?name,?IBinder?service)?{??
????????????remoteService?=?IRemoteService.Stub.asInterface(service);??
????????????//注冊回調??
????????????try?{??
????????????????remoteService.register(remoteCallback);??
????????????}?catch?(RemoteException?e)?{??
????????????????e.printStackTrace();??
????????????}??
}??

?IBinder service是從RemoteService返回的IRemoteService.Stub iBinder，這個對象是Server應用進程中的對象。

IRemoteService.Stub.asInterface(service)在本地創建了一個代理

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);//這里肯定返回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);//創建一個本地代理

}

當使用remoteService調用方法時，其實是調用了本地com.example.aidl.IRemoteService.Stub.Proxy對象的方法，從Proxy方法中可以看到，每個方法都執行了mRemote.transact(Stub.TRANSACTION_xxx, _data, _reply, 0);。

如：

Java代碼 ?

//獲取狀態??
??
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;??
}??

?這一過程是把Client端的參數轉換成Parcel（_data）傳遞到Server端，而在Server端又會把返回數據保存到_reply中，這就形成了一次交互。

mRemote是遠程對象，transact方法會執行onTransact方法

Java代碼 ?

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;??
????}??

?這樣就會執行遠程的onTransact方法，

Java代碼 ?

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);，這就調用了Server端的getStatus(String flag)，并把返回結果寫到Client端的代理Proxy對象的_reply中

到此，aidl通信過程就完成了。

PS: aidl通信有點復雜，但仔細分析并不是很難

總結

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