使用 Android 原生 Binder 发送自定义对象

Question

我只能找到有关 Parcelable 的 Java 示例。 我的目标是用原生 C++（不是 NDK）创建一个简单的服务和客户端，它将使用 Binder 来接收和发送序列化的自定义对象。

MyClass
+ std::string
+ enum
+ int
+ bool

Answer 1

由于您使用的是 Android 5.1，我将坚持使用 Lollipop 上提供的内容。 有更好的工具，比如aidl-cpp来实现这一点，这样可以省去很多手动滚动样板代码的麻烦。

首先，在IFooService.h为服务制作接口。

class IFooService: public IInterface {
    public:
        DECLARE_META_INTERFACE(FooService);
        virtual int myFunc(const String8& str, int enumParam, int intParam, int boolParam) = 0;

};

然后编写服务的编组代码，根据问题中的要求实现功能

class BnFooService: public BnInterface<IFooService>
{
public:
    virtual status_t    onTransact( uint32_t code,
                                    const Parcel& data,
                                    Parcel* reply,
                                    uint32_t flags = 0);
};

enum {
    MY_FUNC = IBinder::FIRST_CALL_TRANSACTION,
};

/* BinderProxy code, for clients of the service to call into the service and have
   the paremeters marshalled properly across the Binder interface. Executes in the
   client process context
 
*/
class BpFooService: public BpInterface<IFooService> {
public:
    virtual int myFunc(const String8& str, int enumParam, int intParam, int boolParam) {
        //2 Parcel objects, 1 to write the data to and another to receive it in
        Parcel data, reply;
        //This serves as the token for the Binder framework for a sanity check
        data.writeInterfaceToken(IFooService::getInterfaceDescriptor());
        data.writeString8(str);
        data.writeInt32(enumParam);
        data.writeInt32(intParam);
        data.writeInt32(boolParam);
        return remote()->transact(MY_FUNC, data, &reply);
    }
}

IMPLEMENT_META_INTERFACE(MediaPlayerService, "com.somedomain.IFooService");

/* Actual Binder implementation of the service which unpacks the data from the
   incoming Parcel and handles the call accordingly     
*/
status_t BnFooService::onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) {
    switch (code) {
        case MY_FUNC: {
            //The same token is checked
            CHECK_INTERFACE(IFooService, data, reply);
            //Read off in exact same order as written to the data Parcel above
            String8 str = data.readString8();
            int enumParam = data.readInt32();
            int intParam = data.readInt32();
            int boolParam = data.readInt32();
            reply->writeInt32(myFunc(str, enumParam, intParam, boolParam));
            return NO_ERROR;
        }
        break;
    default:
        
}

然后使用如下代码创建main_foo.cpp作为服务进程的入口点：

int main() {
    if(!FooService::publish()) { //Call into your code to register with ServiceManager
        ALOGE("Can't instantiate FooService! Exiting");
        return 1;
    }
    ProcessState::self()->startThreadPool(); //Required for the binder threads
    IPCThreadState::self()->joinThreadPool(); //Infinite loop that waits for inbound connections
}

最后，在FooService.cpp实现服务的接口

bool FooService::publish() {
    defaultServiceManager()->addService(String16("foo_service"), new FooService());
    sp<IBinder> binder = defaultServiceManager()->checkService(String16("foo_service"));
    while(binder == NULL && /*some upper time limit*/){
        ALOGI("Waiting for foo_service");
    }
    return binder != NULL;
}

int FooService::myFunc(const String8& str, int enumParam, int intParam, int boolParam) {
    //business logic
    return 0;
}

请注意，这不是适用于常规应用程序开发人员的代码，而是适用于在 Android 框架中运行的本机服务，如InputFlinger 、 SurfaceFlinger等。此代码需要框架头文件，如Parcel.h 、 IInterface.h等，这些文件不可用在 SDK 中。