最近一个项目需要将Android的nfc接口底层通过串口对接到外围一个单片机上,而nfc设备是接在单片机上的,这就需要对Android的nfc框架进行梳理,确定与单片机对接的接口通讯;上网查找发现资料不少,本次分析主要参考了以下大神的博客,基本上已经是非常清楚了!按照自己的理解对相关部分进行整理!
nfc的相关背景知识请参照此博客查阅即可:
以下以开机,并且一个读卡流程,一一介绍整个顺序:
一、开机启动Nfc服务流程:
Android5.0\frameworks\base\services\core\Java\com\android\server\am\ActivityManagerService.java
public void systemReady(final RunnablegoingCallback) {
....
if (mFactoryTest !=FactoryTest.FACTORY_TEST_LOW_LEVEL) {
try {
List apps =AppGlobals.getPackageManager().
getPersistentApplications(STOCK_PM_FLAGS);
if (apps != null) {
int N = apps.size();
int i;
for (i=0; i<N; i++){
ApplicationInfoinfo
=(ApplicationInfo)apps.get(i);
if (info != null &&
!info.packageName.equals("android")) {
addAppLocked(info, false, null /* ABI override */);
}
}
}
} catch (RemoteException ex) {
// pm is in same process,this will never happen.
}
}
...
}
继续分析addAppLocked()
final ProcessRecordaddAppLocked(ApplicationInfo info, boolean isolated,
String abiOverride) {
...
if (app.thread == null &&mPersistentStartingProcesses.indexOf(app) < 0) {
mPersistentStartingProcesses.add(app);
startProcessLocked(app, "addedapplication", app.processName, abiOverride,
null /* entryPoint */, null /*entryPointArgs */);
}
...
}
最终会call到NfcApplication.java中的NfcApplication()构造函数,其中的onCreate()会被调用到。
@Override
public void onCreate() {
super.onCreate();
boolean isMainProcess = false;
// We start a service in a separateprocess to do
// handover transfer. We don't want toinstantiate an NfcService
// object in those cases, hence checkthe name of the process
// to determine whether we're the mainNFC service, or the
// handover process
ActivityManager am =(ActivityManager)this.getSystemService(ACTIVITY_SERVICE);
List processes =am.getRunningAppProcesses();
Iterator i = processes.iterator();
while (i.hasNext()) {
//检查当前运行的App名字是否为"com.android.nfc",如果名字相同,则表示当前启动的程序是主程序
RunningAppProcessInfo appInfo =(RunningAppProcessInfo)(i.next());
if (appInfo.pid == Process.myPid()){
isMainProcess = (NFC_PROCESS.equals(appInfo.processName));
break;
}
}
if (UserHandle.myUserId() == 0&& isMainProcess) {</span>
//启动NfcService
mNfcService = new NfcService(this);
HardwareRenderer.enableForegroundTrimming();
}
}
当调用了new NfcService()之后,后面会依次创建各个Service。
在进行后续分析前,简单的列举一下NFC的类图,方便后续的理解:
上层APP主要透过调用android.nfc.tech及android.nfc的接口来实现期望的功能;而android.nfc.tech和android.nfc透过AIDL的方式调用到NfcService中的接口。Framework中NfcService透过JNI与底层NFC Driver进行沟通,实现发送命令和接收event功能。
在进入NFCService.java前,需要对整个系统的架构有个初步的了解。
DeviceHost.java定义了目前几乎NFC需要的全部interface和API。不同的厂家依据DeviceHost.java提供的interface,实现对应的内容,就可以和上层app进行沟通了。
二、开机启动流程2:
NfcService对象,具体的流程就略过了!请查看对应的博客即可;
三、接下来开始描述一整个读卡流程:
1、Android app打开nfc为开始
首先是app上,4.4以前通过以下调用打开:
var1 = NfcAdapter.getDefaultAdapter(this.t)
PendingIntent var3 = PendingIntent.getActivity(this.t, 0, (new Intent(this.t, this.t.getClass())).addFlags(536870912), 0);
IntentFilter[] var4 = new IntentFilter[0];
var1.enableForegroundDispatch((Activity)this.t, var3, var4, (String[][])null);
本文以Android 5.1版本描述读卡流程,5.1版本通过以下调用打开:
a、重写Callback
nfcCallBack = new NfcAdapter.ReaderCallback() {
@Override
public void onTagDiscovered(Tag tag) {
// TODO Auto-generated method stub
if(isNFC)
{
Message message = new Message();
message.what = NFC_START;
message.obj = tag;
mHandler.sendMessage(message);
}
}
};
然后通过打开nfc
public boolean EnableSystemNFCMessage(ReaderCallback var1) {
try {
NfcAdapter var2;
if((var2 = NfcAdapter.getDefaultAdapter(this.t)) != null && var2.isEnabled()) {
Bundle var3;
(var3 = new Bundle()).putInt("presence", 3000);
var2.enableReaderMode((Activity)this.t, var1, d, var3);
return true;
} else {
return false;
}
} catch (Exception var4) {
var4.printStackTrace();
return false;
}
}
2、此时进入framework中,下面一个个记录调用顺序,本阶段为开启nfc扫描:
frameworks/base/core/java/android/nfc/NfcAdapter.java:1276
public void enableReaderMode(Activity activity, ReaderCallback callback, int flags,Bundle extras)
frameworks/base/core/java/android/nfc/NfcActivityManager.java:206
public void enableReaderMode(Activity activity, ReaderCallback callback, int flags,Bundle extras)
public void setReaderMode(Binder token, int flags, Bundle extras)
PS:此处NfcAdapter.sService是通过NfcAdapter.java中的ServiceManager.getService("nfc")获取的,实际就是实例化packages/apps/Nfc/src/com/android/nfc/NfcService.java服务时,在构造函数中通过ServiceManager.addService(SERVICE_NAME, mNfcAdapter); 加入的,实际为NfcAdapterService实例
接上调用到:
packages/apps/Nfc/src/com/android/nfc/NfcService.java
935行:public void setReaderMode(IBinder binder, IAppCallback callback, int flags, Bundle extras)
接着进入1441行:void applyRouting(boolean force)
mDeviceHost.enableDiscovery(newParams, shouldRestart);
packages/apps/Nfc/nxp/src/com/android/nfc/dhimpl/NativeNfcManager.java(以nxp框架为例)
167行:调用doEnableDiscovery函数,进入jni
packages/apps/Nfc/nxp/jni/com_android_nfc_NativeNfcManager.cpp
static void com_android_nfc_NfcManager_enableDiscovery(JNIEnv *e, jobject o, jint modes, jboolean, jboolean reader_mode, jboolean enable_p2p, jboolean restart)
注册扫描nfc卡回调 ret = phLibNfc_RemoteDev_NtfRegister(&nat->registry_info, nfc_jni_Discovery_notification_callback, (void *)nat)
3、至此,设备开始进行nfc扫描;
接下来分析扫描到nfc卡之后,从调用回调函数开始:
packages/apps/Nfc/nxp/jni/com_android_nfc_NativeNfcManager.cpp
905行: static void nfc_jni_Discovery_notification_callback(void *pContext, phLibNfc_RemoteDevList_t *psRemoteDevList, uint8_t uNofRemoteDev, NFCSTATUS status)
其中判断nfc类型,依照类型实例化cached_NfcTag(非接卡)或者cached_P2pDevice(Nfc设备),以下以非接卡继续说明:
1、实例化
ScopedLocalRef<jclass> tag_cls(e, e->GetObjectClass(nat->cached_NfcTag));
jmethodID ctor = e->GetMethodID(tag_cls.get(), "<init>", "()V");
tag.reset(e->NewObject(tag_cls.get(), ctor)); //以上三行实际就是获得cached_NfcTag的构造函数,然后将tag实例化为cached_NfcTag
PS:通过1629行:if(nfc_jni_cache_object(e,"com/android/nfc/dhimpl/NativeNfcTag",&(nat->cached_NfcTag)) == -1) 可知,cached_NfcTag实际就是packages/apps/Nfc/nxp/src/com/android/nfc/dhimpl/NativeNfcTag.java类 (implements TagEndpoint)
接下来将NativeNfcTag实例的各个数值初始化,包括支持的协议等,最后
e->CallVoidMethod(nat->manager, cached_NfcManager_notifyNdefMessageListeners, tag.get());通知上层进行处理
实际就是:
packages/apps/Nfc/nxp/src/com/android/nfc/dhimpl/NativeNfcManager.java
360行:private void notifyNdefMessageListeners(NativeNfcTag tag)
packages/apps/Nfc/src/com/android/nfc/NfcService.java
236行:public void onRemoteEndpointDiscovered(TagEndpoint tag)
sendMessage(NfcService.MSG_NDEF_TAG, tag);
本文件中的final class NfcServiceHandler extends Handler中对此消息进行处理;
播放声音等,然后调用
tag.startPresenceChecking(presenceCheckDelay, callback);
dispatchTagEndpoint(tag, readerParams);等发送消息到上层
最终在dispatchTagEndpoint中,调用回调将TagEndpoint,根据相应的信息,转换为tag类传到应用层;PS:最重要此处将TagService封装进了Tag类中
if (readerParams.callback != null) {
readerParams.callback.onTagDiscovered(tag);
4、接下来又回到应用层,接收到nfc检测Tag:
应用层获取到Tag类之后,判断Tag类型后,可以通过具体的封装,获取对应的协议类进行处理,以下以NfcB举例:
this.A = NfcB.get(var1);
try {
this.A.connect();
if(this.A.isConnected()) {
this.B = new m(this.A);
return true;
}
} catch (IOException var7) {
}
5、接下来应用可以自行调用NfcB等协议进行nfc卡的读写操作,以NfcB协议举例,西面是相关方法在framework中的位置:
frameworks/base/core/java/android/nfc/tech/NfcB.java
继承自frameworks/base/core/java/android/nfc/tech/BasicTagTechnology.java
内部依据具体的协议内容,最终通过传入的Tag类,获取TagService服务,通过TagService服务最终调用到NativeNfcTag中相应的connect,transceive等方法,与非接卡进行通讯;
自此,以流水账的形式将一个nfc的读卡流程描写完成!整体描述比较晦涩,后续再看看怎么样能够更好的表达记录nfc读卡流程!