通过Binder实现 Native Service

这次从理论联系实际，参考MediaPlayerService来实现自己需要的Service

注意：下面的代码只在Android N上验证，Android O 编译规则比较严格，warning的也会报错

一、理论分析

从之前分析MediaPlayerService的结果可以得到如下结果：

从图中可以看出，我们需要自己实现：

1. IXXXService
2. BpXXXService
3. BnXXXService
4. XXXService

如果我们要实现TestPlayService并包含一个check方法，那么如下图：

1. ITestPlayService.h
   这里除了定义了ITestPlayService，还定义了BnTestPlayService，
2. ITestPlayService.cpp
   这里定义了BpTestPlayService
   实现了BnTestPlayService的onTransact方法
   BpTestPlayService实现了ITestPlayService中声明的方法
3. TestPlayService.h
   这里定义了服务端
4. TestPlayService.cpp
   实现了TestPlayService.h中定义的方法

二、具体实现

1. ITestPlayService.h

#include <binder/IInterface.h>namespace android {class ITestPlayService: public IInterface{public:    DECLARE_META_INTERFACE(TestPlayService);    virtual void check(uint32_t params) const = 0;};class BnTestPlayService: public BnInterface<ITestPlayService>{public:    virtual status_t    onTransact( uint32_t code,                                    const Parcel& data,                                    Parcel* reply,                                    uint32_t flags = 0);};};

2. ITestPlayService.cpp

#include <binder/Parcel.h>#include "ITestPlayService.h"namespace android {enum {    //这里有一点疑问，开始我觉得"= IBinder::FIRST_CALL_TRANSACTION"这个是一定要加的，因为服务端是根据enum中的顺序来识别客户端的请求的    //但是我注释到这句，发现程序依然可以运行，这点有待查看    CHECK = IBinder::FIRST_CALL_TRANSACTION,  };class BpTestPlayService: public BpInterface<ITestPlayService>{public:    explicit BpTestPlayService(const sp<IBinder>& impl)        : BpInterface<ITestPlayService>(impl)    {    }    virtual void check(uint32_t params) const {        Parcel data, reply;        data.writeInterfaceToken(ITestPlayService::getInterfaceDescriptor());        data.writeInt32(params);         remote()->transact(CHECK, data, &reply);    }};IMPLEMENT_META_INTERFACE(TestPlayService, "android.chengming.TestPlayService");status_t BnTestPlayService::onTransact(    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){    switch (code) {    case CHECK: {        CHECK_INTERFACE(ITestPlayService, data, reply);        uint32_t params = data.readInt32();        check(params);        return NO_ERROR;    } break;    default:        return BBinder::onTransact(code, data, reply, flags);    }};};

3. TestPlayService.h

#include "ITestPlayService.h"#include <binder/BinderService.h>namespace android {class TestPlayService : public BinderService<TestPlayService>, public BnTestPlayService{public:    TestPlayService();    //static  void instantiate();    virtual void check(uint32_t params) const;    virtual status_t dump(int fd, const Vector<String16>& args);    static char const* getServiceName() { return "test.player"; }private:    virtual ~TestPlayService();};};

4. TestPlayService.cpp

#define LOG_TAG "TestPlayService"#include <utils/Log.h>#include <binder/IPCThreadState.h>#include <binder/ProcessState.h>#include <binder/IServiceManager.h>#include <unistd.h>#include "TestPlayService.h"namespace android {TestPlayService::TestPlayService() {    ALOGD("TestPlayService created");}TestPlayService::~TestPlayService() {    ALOGD("TestPlayService destroyed");}/*void TestPlayService::instantiate() {    defaultServiceManager()->addService(            String16("test.player"), new TestPlayService());}*/status_t TestPlayService::dump(int fd, const Vector<String16>& args) {    String8 result;    ALOGD("dump() is called.");    result = "dump";    write(fd, result.string(), result.size());    return NO_ERROR;}void TestPlayService::check(uint32_t params) const {    if(params == 5) {        ALOGI("params yes");    }else {        ALOGI("params no");    }}};

5. main_testplayservice.cpp

#define LOG_TAG "TestPlayService"#include <utils/Log.h>#include <binder/IPCThreadState.h>#include <binder/ProcessState.h>#include <binder/IServiceManager.h>#include "TestPlayService.h"using namespace android;int main(int argc __unused, char **argv __unused){    sp<ProcessState> proc(ProcessState::self());    sp<IServiceManager> sm(defaultServiceManager());    ALOGI("ServiceManager1: %p", sm.get());    //TestPlayService::instantiate();    //ProcessState::self()->startThreadPool();    //IPCThreadState::self()->joinThreadPool();    TestPlayService::publishAndJoinThreadPool();}

6. main_testplayclient.cpp

#define LOG_TAG "TestPlayService"#include <utils/Log.h>#include <binder/IPCThreadState.h>#include <binder/ProcessState.h>#include <binder/IServiceManager.h>#include "ITestPlayService.h"using namespace android;int main(int argc __unused, char **argv __unused){    sp<IBinder> binder;      sp<ProcessState> proc(ProcessState::self());    sp<IServiceManager> sm(defaultServiceManager());    ALOGI("ServiceManager: %p", sm.get());    binder = sm->getService(String16("test.player"));      sp<ITestPlayService> service = interface_cast<ITestPlayService>(binder);    uint32_t params = 5;    service->check(params);    ProcessState::self()->startThreadPool();    IPCThreadState::self()->joinThreadPool();}

7. Android.mk

LOCAL_PATH:= $(call my-dir)include $(CLEAR_VARS)LOCAL_SRC_FILES:= \        TestPlayService.cpp \        ITestPlayService.cpp \        main_testplayservice.cppLOCAL_SHARED_LIBRARIES := \        libutils \        libcutils \        liblog \        libbinderLOCAL_MODULE:= TestPlayServerinclude $(BUILD_EXECUTABLE)include $(CLEAR_VARS)LOCAL_SRC_FILES:= \        ITestPlayService.cpp \        main_testplayclient.cppLOCAL_SHARED_LIBRARIES:= \        libutils \        libcutils \        liblog \        libbinderLOCAL_MODULE:= TestPlayClientinclude $(BUILD_EXECUTABLE)

三、 拓展：

1. 上面是通过TestPlayService::publishAndJoinThreadPool()（TestPlayService继承了BinderService）来把TestPlayService加入到ServiceManager中的
   在Android源码中，大部分用的还是defaultServiceManager()->addService的方式
   其实，这两种方式是差不多的，简单看下publishAndJoinThreadPool函数：
   可以看到最终还是调用了addService方法

    static void publishAndJoinThreadPool(bool allowIsolated = false) {        publish(allowIsolated);        joinThreadPool();    }    static status_t publish(bool allowIsolated = false) {        sp<IServiceManager> sm(defaultServiceManager());        return sm->addService(                String16(SERVICE::getServiceName()),                new SERVICE(), allowIsolated);    }

1. 这里展示的只是简单的例子，监听binder的死亡等见源码：

[e-mail]:ShuttleCheng/TestPlayService.git

四、 注意点：

1. 代码要用namespace android包起来

2. C++ 打印log的方法：
   ALOGD(“onFirstRef() is called.”);
   如果想要加入tag：#define LOG_TAG “TestPlayService”

   注意：
   发现如果使用ALOGV的话，并不会在终端上打出，换成ALOGD即可
   不知道为什么，有空再看下Log系统

编译报错记录：
1.error: allocating an object of abstract class type ‘android::TestPlayService’
一开始总是会报这个错误，网上搜索给出的结果是可能有父类的虚函数没有实现
实际上虚函数已经实现了，丢了个const，原因如下：
在ITestPlayService.h中定义的方法是：
virtual void check(uint32_t params) const = 0;
可是在TestPlayService.h中定义的方法是：
virtual void check(uint32_t params) ; //没有const
有和没有const是两个函数，所以编译会报错