说究竟，Java层的service就是就C++层的binder的封装。所以从原理上来讲通过C++代码直接訪问android framework层的service是全然可能的，这篇文章以訪问WifiService为例，解说怎样去实现这个功能。

费话少说。直接上代码：

WifiTest.cpp

#include <sys/types.h>

#include <unistd.h>

#include <grp.h>

#include <binder/IPCThreadState.h>

#include <binder/ProcessState.h>

#include <binder/IServiceManager.h>

#include <utils/Log.h>

#include <utils/String16.h>

//#include <utils/Vector.h>

#include <utils/List.h>

#include <utils/PropertyMap.h>

using namespace android;

#define WIFI_SERVICE  "wifi"

const String16 WIFI_DESCRIPTOR("android.net.wifi.IWifiManager");

class ScanResult

{

private:

    ScanResult& operator=(const ScanResult& o);

public:

    ScanResult(const ScanResult& o):

        mSsid(o.mSsid),mBssid(o.mBssid),mCaps(o.mCaps),mLevel(o.mLevel),mFrequency(o.mFrequency),mTimestamp(o.mTimestamp)

    {

    }

    ScanResult(String8 ssid,String16 bssid,String16 caps,int level,int freq,int64_t timeStamp):

        mSsid(ssid),mBssid(bssid),mCaps(caps),mLevel(level),mFrequency(freq),mTimestamp(timeStamp)

    {

    }

    void dump()

    {

        char temp[130];

        int size;

        memset(temp,0,sizeof(temp));

        printf("ssid %s \n",mSsid.string());

        size = mBssid.size();

        if(size > sizeof(temp)/2 - 1)

        {

            size = sizeof(temp)/2 - 1;

        }

        utf16_to_utf8(mBssid.string(), size, temp);

        printf("Bssid %s \n",temp);

        size = mCaps.size();

        if(size > sizeof(temp)/2 - 1)

        {

            size = sizeof(temp)/2 - 1;

        }

        utf16_to_utf8(mCaps.string(), size, temp);

        printf("ssid %s \n",temp);

        printf("level %d \n",mLevel);

        printf("freq %d \n",mFrequency);

        printf("freq %ld \n",mTimestamp);

    }

private:

    String8 mSsid;

    String16 mBssid;

    String16 mCaps;

    int mLevel;

    int mFrequency;

    int64_t mTimestamp;

};

class IWifiService: public android::IInterface {

public:

        DECLARE_META_INTERFACE(WifiService)

        virtual void startScan(int forceActive) = 0;

        virtual int getScanResults(List<ScanResult> &list) = 0;

        virtual bool setWifiEnabled(bool enable) = 0;

};

class BpWifiService: public android::BpInterface<IWifiService>

{

    enum

    {

        FIRST_CALL_TRANSACTION = 1,

        TRANSACTION_getConfiguredNetworks = (android::IBinder::FIRST_CALL_TRANSACTION + 0),

        TRANSACTION_addOrUpdateNetwork = (android::IBinder::FIRST_CALL_TRANSACTION + 1),

        TRANSACTION_removeNetwork = (android::IBinder::FIRST_CALL_TRANSACTION + 2),

        TRANSACTION_enableNetwork = (android::IBinder::FIRST_CALL_TRANSACTION + 3),

        TRANSACTION_disableNetwork = (android::IBinder::FIRST_CALL_TRANSACTION + 4),

        TRANSACTION_pingSupplicant = (android::IBinder::FIRST_CALL_TRANSACTION + 5),

        TRANSACTION_startScan = (android::IBinder::FIRST_CALL_TRANSACTION + 6),

        TRANSACTION_getScanResults = (android::IBinder::FIRST_CALL_TRANSACTION + 7),

        TRANSACTION_disconnect = (android::IBinder::FIRST_CALL_TRANSACTION + 8),

        TRANSACTION_reconnect = (android::IBinder::FIRST_CALL_TRANSACTION + 9),

        TRANSACTION_reassociate = (android::IBinder::FIRST_CALL_TRANSACTION + 10),

        TRANSACTION_getConnectionInfo = (android::IBinder::FIRST_CALL_TRANSACTION + 11),

        TRANSACTION_setWifiEnabled = (android::IBinder::FIRST_CALL_TRANSACTION + 12),

        TRANSACTION_getWifiEnabledState = (android::IBinder::FIRST_CALL_TRANSACTION + 13),

        TRANSACTION_setCountryCode = (android::IBinder::FIRST_CALL_TRANSACTION + 14),

        TRANSACTION_setFrequencyBand = (android::IBinder::FIRST_CALL_TRANSACTION + 15),

        TRANSACTION_getFrequencyBand = (android::IBinder::FIRST_CALL_TRANSACTION + 16),

        TRANSACTION_isDualBandSupported = (android::IBinder::FIRST_CALL_TRANSACTION + 17),

        TRANSACTION_saveConfiguration = (android::IBinder::FIRST_CALL_TRANSACTION + 18),

        TRANSACTION_getDhcpInfo = (android::IBinder::FIRST_CALL_TRANSACTION + 19),

        TRANSACTION_acquireWifiLock = (android::IBinder::FIRST_CALL_TRANSACTION + 20),

        TRANSACTION_updateWifiLockWorkSource = (android::IBinder::FIRST_CALL_TRANSACTION + 21),

        TRANSACTION_releaseWifiLock = (android::IBinder::FIRST_CALL_TRANSACTION + 22),

        TRANSACTION_initializeMulticastFiltering = (android::IBinder::FIRST_CALL_TRANSACTION + 23),

        TRANSACTION_isMulticastEnabled = (android::IBinder::FIRST_CALL_TRANSACTION + 24),

        TRANSACTION_acquireMulticastLock = (android::IBinder::FIRST_CALL_TRANSACTION + 25),

        TRANSACTION_releaseMulticastLock = (android::IBinder::FIRST_CALL_TRANSACTION + 26),

        TRANSACTION_setWifiApEnabled = (android::IBinder::FIRST_CALL_TRANSACTION + 27),

        TRANSACTION_getWifiApEnabledState = (android::IBinder::FIRST_CALL_TRANSACTION + 28),

        TRANSACTION_getWifiApConfiguration = (android::IBinder::FIRST_CALL_TRANSACTION + 29),

        TRANSACTION_setWifiApConfiguration = (android::IBinder::FIRST_CALL_TRANSACTION + 30),

        TRANSACTION_startWifi = (android::IBinder::FIRST_CALL_TRANSACTION + 31),

        TRANSACTION_stopWifi = (android::IBinder::FIRST_CALL_TRANSACTION + 32),

        TRANSACTION_addToBlacklist = (android::IBinder::FIRST_CALL_TRANSACTION + 33),

        TRANSACTION_clearBlacklist = (android::IBinder::FIRST_CALL_TRANSACTION + 34),

        TRANSACTION_getWifiServiceMessenger = (android::IBinder::FIRST_CALL_TRANSACTION + 35),

        TRANSACTION_getWifiStateMachineMessenger = (android::IBinder::FIRST_CALL_TRANSACTION + 36),

        TRANSACTION_getConfigFile = (android::IBinder::FIRST_CALL_TRANSACTION + 37),

        TRANSACTION_captivePortalCheckComplete = (android::IBinder::FIRST_CALL_TRANSACTION + 38),

    };

public:

        BpWifiService(const android::sp<android::IBinder>& impl): android::BpInterface<IWifiService>(impl)

        {

        }

        void startScan(int forceActive)

        {

            android::Parcel data, reply;

            data.writeInterfaceToken(WIFI_DESCRIPTOR);

            if (forceActive)

            {

                data.writeInt32(1);

            }

            else

            {

                data.writeInt32(0);

            }

            remote()->transact(TRANSACTION_startScan, data, &reply, 0);

        }

        virtual int getScanResults(List<ScanResult> &list)

        {

            Parcel data, reply;

            data.writeInterfaceToken(WIFI_DESCRIPTOR);

            remote()->transact(TRANSACTION_getScanResults, data, &reply, 0);

            if (0 != reply.readExceptionCode())

            {

                return 0;

            }

            int count = reply.readInt32();

            for (int i=0;i<count;i++)

            {

                String8 ssid;

                int res =  reply.readInt32();

                if (res != 0)

                {

                    reply.readInt32();

                    reply.readInt32();

                    int length = reply.readInt32();

                    ssid = String8((const char*)reply.readInplace(length),length);

                }

//                utf16_to_utf8(const char16_t* src, size_t src_len, char* dst);

                String16 BSSID = reply.readString16();

                String16 caps = reply.readString16();

                int level = reply.readInt32();

                int frequency = reply.readInt32();

                int64_t timestamp = reply.readInt64();

                ScanResult result(ssid,BSSID,caps,level,frequency,timestamp);

                list.push_back(result);

            }

            return count;

        }

        bool setWifiEnabled(bool enable)

        {

            Parcel data, reply;

            data.writeInterfaceToken(WIFI_DESCRIPTOR);

            if(enable)

                data.writeInt32(1);

            else

                data.writeInt32(0);

            remote()->transact(TRANSACTION_setWifiEnabled, data,&reply,0);

            reply.readExceptionCode();

            return 0!=reply.readInt32();

        }

};

IMPLEMENT_META_INTERFACE(WifiService, WIFI_DESCRIPTOR)

int main(int argc, char *argv[])

{

    android::sp<android::IServiceManager> sm = android::defaultServiceManager();

    android::sp<android::IBinder> binder;

    android::sp<IWifiService> wifi;

    binder = sm->getService(android::String16(WIFI_SERVICE));

    if (binder == 0)

    {

        return 1;

    }

    wifi = android::interface_cast<IWifiService>(binder);

    wifi->setWifiEnabled(true);

	printf("+++++scan start");

	wifi->startScan(1);

	for(int i=0;i<10;i++)

	{

		usleep(1*1000*1000);

		List<ScanResult> list;

		wifi->getScanResults(list);

		if(list.size() > 0)

	    {

	        for(List<ScanResult>::iterator it = list.begin();it != list.end();++it)

	        {

	            (*it).dump();

	        }

	        break;

	    }

	}

    return(0);

}

主要的思路非常easy：

先通过：

android::defaultServiceManager()->getService(android::String16(WIFI_SERVICE));

获取binder接口。再通过Parcel读与binder，详细的实现能够參考IWifiManager.java的代码。

编译后执行以上的代码能够得到类似下面的输出：

ssid wifitest

Bssid b8:55:10:84:13:57

ssid [WPA-PSK-CCMP][WPA2-PSK-CCMP][WPS][ESS]

level -55

freq 2447

time stamp 1073922473

ssid test

Bssid 08:bd:43:c3:a9:96

ssid [WPA2-PSK-CCMP][WPS][ESS]

level -66

freq 2462

time stamp 1073922473

完整代码下载：

http://download.csdn.net/detail/i2cbus/7613361

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