interface宏：DECLARE_META_INTERFACE/IMPLEMENT_META_INTERFACE

frameworks/native/include/binder/IInterface.h:

#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() { }                                   \

在framework/native/include/binder/IServiceManager.h中：

class IServiceManager : public IInterface
{
public:
    DECLARE_META_INTERFACE(ServiceManager);

展开它：

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