Android Binder之基本类介绍

最新推荐文章于 2025-03-28 00:11:50 发布

东晋偏安

最新推荐文章于 2025-03-28 00:11:50 发布

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分类专栏： android 文章标签： Android IPC Binder

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============================================================================

在学习Android Binder之前，需要对如下几个类、一个模板函数和两个关键宏有所了解：

1）IBinder、BBinder、BpRefBase 、BpBinder、IInterface、模板类BnInterface、模板类BpInterface

2）模板函数interface_cast

3）两个关键宏：DECLARE_META_INTERFACE(INTERFACE)和IMPLEMENT_META_INTERFACE(INTERFACE, NAME)

============================================================================

// IBinder.h

// 类IBinder是Binder通信协议的接口，为client和server端通信的基础。

// 类BBinder和类BpBinder均为IBinder的子类：BBinder用于server端，BpBinder用于client端。

/**
 * Base class and low-level protocol for a remotable object.
 * You can derive from this class to create an object for which other
 * processes can hold references to it.  Communication between processes
 * (method calls, property get and set) is down through a low-level
 * protocol implemented on top of the transact() API.
 */
class IBinder : public virtual RefBase
{
public:
    /**
     * Return the canonical name of the interface provided by this IBinder
     * object.
     */
    virtual const String16& getInterfaceDescriptor() const = 0;

    virtual status_t        transact(   uint32_t code,
                                        const Parcel& data,
                                        Parcel* reply,
                                        uint32_t flags = 0) = 0;

    virtual BBinder*        localBinder();
    virtual BpBinder*       remoteBinder();

protected:
    virtual          ~IBinder();
};

// Binder.h

类BBinder继承自IBinder，用于server端。各个服务端的service（比如ServiceManager、MediaPlayerService等等）需要创建一个继承BBinder并实现onTransact（）函数的class，比如BnXXXService。BBinder通过transact（）接收处理client端发过来的请求命令，并调用onTransact()这个虚函数，即调用BnXXXService的onTransact（）函数。

类BpRefBase 的作用：client 端通过查询ServiceManager 获取到所需的的 BpBinder 后， BpRefBase 负责管理当前获得的 BpBinder 实例，并保存至成员变量IBinder* const mRemote;

class BBinder : public IBinder
{
public:
                        BBinder();

    virtual const String16& getInterfaceDescriptor() const;
    virtual bool        isBinderAlive() const;

    virtual status_t    transact(   uint32_t code,
                                    const Parcel& data,
                                    Parcel* reply,
                                    uint32_t flags = 0);

    virtual BBinder*    localBinder();

protected:
    virtual             ~BBinder();

    virtual status_t    onTransact( uint32_t code,
                                    const Parcel& data,
                                    Parcel* reply,
                                    uint32_t flags = 0);

private:
                        BBinder(const BBinder& o);
            BBinder&    operator=(const BBinder& o);

    class Extras;

            Extras*     mExtras;
            void*       mReserved0;
};


class BpRefBase : public virtual RefBase
{
protected:
                            BpRefBase(const sp<IBinder>& o);
    virtual                 ~BpRefBase();

    inline  IBinder*        remote()                { return mRemote; }
    inline  IBinder*        remote() const          { return mRemote; }

private:
                            BpRefBase(const BpRefBase& o);
    BpRefBase&              operator=(const BpRefBase& o);

    IBinder* const          mRemote;
};

// BpBinder.h

类BpBinder继承自IBinder，负责将client端的请求发送至服务端的BBinder，为服务端在client端所提供的服务代理。客户端必须通过服务代理BpBinder才可以享用服务端所提供的具体服务。

class BpBinder : public IBinder
{
public:
                        BpBinder(int32_t handle);

    inline  int32_t     handle() const { return mHandle; }

    virtual const String16&    getInterfaceDescriptor() const;
    virtual bool        isBinderAlive() const;

    virtual status_t    transact(   uint32_t code,
                                    const Parcel& data,
                                    Parcel* reply,
                                    uint32_t flags = 0);

    virtual BpBinder*   remoteBinder();

private:
    const   int32_t             mHandle;
};

// IInterface.h

类IInterface为所有的server端的共同基类，它的子类，比如IServiceManager、IMediaPlayerService等等提供了该服务端所具备的所有功能（一些列API）。

模板函数：

template<typename INTERFACE> inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
return INTERFACE::asInterface(obj);
}

用法：

sp<IMediaPlayerService> sMediaPlayerService;
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder;
binder = sm->getService(String16("media.player"));
sMediaPlayerService = interface_cast<IMediaPlayerService>(binder);

模板类BnInterface（template<typename INTERFACE> class BnInterface : public INTERFACE, public BBinder）继承自传入的类INTERFACE和BBinder；

模板类BpInterface（template<typename INTERFACE> class BpInterface : public INTERFACE, public BpRefBase）继承自传入的类INTERFACE和BpRefBase。

// ----------------------------------------------------------------------

class IInterface : public virtual RefBase
{
public:
            IInterface();
            sp<IBinder>         asBinder();
            sp<const IBinder>   asBinder() const;
            
protected:
    virtual                     ~IInterface();
    virtual IBinder*            onAsBinder() = 0;
};

// ----------------------------------------------------------------------

template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
    return INTERFACE::asInterface(obj);
}

// ----------------------------------------------------------------------

template<typename INTERFACE>
class BnInterface : public INTERFACE, public BBinder
{
public:
    virtual sp<IInterface>      queryLocalInterface(const String16& _descriptor);
    virtual const String16&     getInterfaceDescriptor() const;

protected:
    virtual IBinder*            onAsBinder();
};

// ----------------------------------------------------------------------

template<typename INTERFACE>
class BpInterface : public INTERFACE, public BpRefBase
{
public:
                                BpInterface(const sp<IBinder>& remote);

protected:
    virtual IBinder*            onAsBinder();
};

// ----------------------------------------------------------------------

#define DECLARE_META_INTERFACE(INTERFACE)                               \
    static const android::String16 descriptor;                          \
    static android::sp<I##INTERFACE> asInterface(                       \
            const android::sp<android::IBinder>& obj);                  \
    virtual const android::String16& getInterfaceDescriptor() const;    \
    I##INTERFACE();                                                     \
    virtual ~I##INTERFACE();                                            \


#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME)                       \
    const android::String16 I##INTERFACE::descriptor(NAME);             \
    const android::String16&                                            \
            I##INTERFACE::getInterfaceDescriptor() const {              \
        return I##INTERFACE::descriptor;                                \
    }                                                                   \
    android::sp<I##INTERFACE> I##INTERFACE::asInterface(                \
            const android::sp<android::IBinder>& obj)                   \
    {                                                                   \
        android::sp<I##INTERFACE> intr;                                 \
        if (obj != NULL) {                                              \
            intr = static_cast<I##INTERFACE*>(                          \
                obj->queryLocalInterface(                               \
                        I##INTERFACE::descriptor).get());               \
            if (intr == NULL) {                                         \
                intr = new Bp##INTERFACE(obj);                          \
            }                                                           \
        }                                                               \
        return intr;                                                    \
    }                                                                   \
    I##INTERFACE::I##INTERFACE() { }                                    \
    I##INTERFACE::~I##INTERFACE() { }                                   \

// ----------------------------------------------------------------------

关于DECLARE_META_INTERFACE(INTERFACE)和IMPLEMENT_META_INTERFACE(INTERFACE, NAME)这两个宏，以MediaPlayerClient为例说明如下：

// ----------------------------------------------------------------------

#define DECLARE_META_INTERFACE(MediaPlayerClient)// 展开如下：                       
    static const android::String16 descriptor;                          
    static android::sp<IMediaPlayerClient> asInterface(                 
            const android::sp<android::IBinder>& obj);                  
    virtual const android::String16& getInterfaceDescriptor() const;    
    IMediaPlayerClient();                                               
    virtual ~IMediaPlayerClient();                                      


#define IMPLEMENT_META_INTERFACE(MediaPlayerClient, "android.media.IMediaPlayerClient")// 展开如下： 
    const android::String16 IMediaPlayerClient::descriptor("android.media.IMediaPlayerClient"); 
    const android::String16&                                           
            IMediaPlayerClient::getInterfaceDescriptor() const {           
        return IMediaPlayerClient::descriptor;                                
    }                                                                   
    android::sp<IMediaPlayerClient> IMediaPlayerClient::asInterface(             
            const android::sp<android::IBinder>& obj)                   
    {                                                                  
        android::sp<IMediaPlayerClient> intr;                               
        if (obj != NULL) {                                             
            intr = static_cast<IMediaPlayerClient*>(                         
                obj->queryLocalInterface(                               
                        IMediaPlayerClient::descriptor).get());               
            if (intr == NULL) {                                         
                intr = new BpMediaPlayerClient(obj);                          
            }                                                          
        }                                                               
        return intr;                                                    
    }                                                                  
    IMediaPlayerClient::IMediaPlayerClient() { }                                   
    IMediaPlayerClient::~IMediaPlayerClient() { }                                  

// ----------------------------------------------------------------------