前言
之前介绍了车载应用开发体系中如何使用Jetpack在HMI中构建MVVM架构Android 车载应用开发与分析 （3）- 构建 MVVM 架构(Java版)，通过之前的介绍，也了解到在大多数车载系统应用架构中，一个完整的应用往往会包含三层，分别是
HMI
Human Machine Interface，显示UI信息，进行人机交互。Service
在系统后台进行数据处理，监控数据状态。SDK
根据业务逻辑，需要Service对外暴露的通信接口，其他模块通过SDK来完成与Service通信，通常是基于AIDL接口。
本篇主要讲解，如何编写基于 AIDL 的 SDK 。
AIDL 介绍
AIDL，Android 接口定义语言，是Android开发中常用的一种进程间通信方式。关于如何使用 AIDL 请参考 Android 接口定义语言 (AIDL) | Android 开发者 | Android Developers
这里介绍一些 AIDL 使用过程中容易混淆的关键字：
- in
interface HvacInterface {
void setData(in Hvac hvac);
}
单向数据流向。被in修饰的参数，会顺利传到Server端，但Servier端对实参的任何改变，都不会回调给Client端。
- out
interface HvacInterface {
void getData(out Hvac hvac);
}
单向数据流向。被out修饰的参数，只有默认值会传到Server端，Servier端对实参的改变，在调用结束后，会回调给Client端。
- inout
interface HvacInterface {
void getData(inout Hvac hvac);
}
inout 则是上面二者的结合，实参会顺利传到Server，且Server对实参的修改，在调用结束后会返回Client端。
- oneway
AIDL 定义的接口默认是同步调用。举个例子：Client端调用setData方法，setData在Server端执行需要耗费5秒钟，那么Client端调用setData方法的线程就会被block5秒钟。如果在setData方法上加上oneway，将接口修改为异步调用就可以避免这个问题。
interface HvacInterface {
oneway void setData(in Hvac hvac);
}
oneway不仅可以修饰方法，也可以用来修饰在interface本身，这样interface内所有的方法都隐式地带上oneway。被oneway修饰了的方法不可以有返回值，也不可以再用out或inout修饰参数。
AIDL 常规用法
IRemoteService iRemoteService;
private ServiceConnection mConnection = new ServiceConnection() {
// Called when the connection with the service is established
public void onServiceConnected(ComponentName className, IBinder service) {
// Following the example above for an AIDL interface,
// this gets an instance of the IRemoteInterface, which we can use to call on the service
iRemoteService = IRemoteService.Stub.asInterface(service);
}
// Called when the connection with the service disconnects unexpectedly
public void onServiceDisconnected(ComponentName className) {
Log.e(TAG, "Service has unexpectedly disconnected");
iRemoteService = null;
}
};
public void setData(Hvac havc){
if (iRemoteService!=null){
iRemoteService.setData(hvac);
}
}
常规的用法中，我们需先判断Client端是否已经绑定上Server端，不仅Client端对Server端的接口调用，也要防止绑定失败导致的空指针。
车载应用中上述的常规用法不仅会使HMI开发变得繁琐，还需要处理Service异常状态下解除绑定后的状态。下面介绍如何简便的封装SDK
封装SDK Base类
实际开发中，我们把Client端对Service的绑定、重连、线程切换等细节隐藏到SDK中并封装成一个BaseConnectManager，使用时只需要继承BaseConnectManager并传入Service的包名、类名和期望的断线重连时间即可。
public abstract class BaseConnectManager {
private final String TAG = SdkLogUtils.TAG_FWK + getClass().getSimpleName();
private static final String THREAD_NAME = "bindServiceThread";
private final Application mApplication;
private IServiceConnectListener mServiceListener;
private final Handler mChildThread;
private final Handler mMainThread;
private final LinkedBlockingQueue mTaskQueue = new LinkedBlockingQueue<>();
private final Runnable mBindServiceTask = this::bindService;
private final ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
SdkLogUtils.logV(TAG, "[onServiceConnected]");
mProxy = asInterface(service);
Remote.tryExec(() -> {
service.linkToDeath(mDeathRecipient, 0);
});
if (mServiceListener != null) {
mServiceListener.onServiceConnected();
}
handleTask();
mChildThread.removeCallbacks(mBindServiceTask);
}
@Override
public void onServiceDisconnected(ComponentName name) {
SdkLogUtils.logV(TAG, "[onServiceDisconnected]");
mProxy = null;
if (mServiceListener != null) {
mServiceListener.onServiceDisconnected();
}
}
};
private final IBinder.DeathRecipient mDeathRecipient = new IBinder.DeathRecipient() {
@Override
public void binderDied() {
SdkLogUtils.logV(TAG, "[binderDied]");
if (mServiceListener != null) {
mServiceListener.onBinderDied();
}
if (mProxy != null) {
mProxy.asBinder().unlinkToDeath(mDeathRecipient, 0);
mProxy = null;
}
attemptToRebindService();
}
};
private T mProxy;
public BaseConnectManager() {
mApplication = SdkAppGlobal.getApplication();
HandlerThread thread = new HandlerThread(THREAD_NAME, 6);
thread.start();
mChildThread = new Handler(thread.getLooper());
mMainThread = new Handler(Looper.getMainLooper());
bindService();
}
private void bindService() {
if (mProxy == null) {
SdkLogUtils.logV(TAG, "[bindService] start");
ComponentName name = new ComponentName(getServicePkgName(), getServiceClassName());
Intent intent = new Intent();
if (getServiceAction() != null) {
intent.setAction(getServiceAction());
}
intent.setComponent(name);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
mApplication.startForegroundService(intent);
} else {
mApplication.startService(intent);
}
boolean connected = mApplication.bindService(intent, mServiceConnection,
Context.BIND_AUTO_CREATE);
SdkLogUtils.logV(TAG, "[bindService] result " + connected);
if (!connected) {
attemptToRebindService();
}
} else {
SdkLogUtils.logV(TAG, "[bindService] not need");
}
}
protected void attemptToRebindService() {
SdkLogUtils.logV(TAG, "[attemptToRebindService]");
mChildThread.postDelayed(mBindServiceTask, getRetryBindTimeMill());
}
protected void handleTask() {
Runnable task;
while ((task = mTaskQueue.poll()) != null) {
SdkLogUtils.logV(TAG, "[handleTask] poll task form task queue");
mChildThread.post(task);
}
}
public void init() {
bindService();
}
public boolean isServiceConnected() {
return isServiceConnected(false);
}
public boolean isServiceConnected(boolean tryConnect) {
SdkLogUtils.logV(TAG, "[isServiceConnected] tryConnect " + tryConnect + ";isConnected " + (mProxy != null));
if (mProxy == null && tryConnect) {
attemptToRebindService();
}
return this.mProxy != null;
}
public void release() {
SdkLogUtils.logV(TAG, "[release]");
if (this.isServiceConnected()) {
this.mProxy.asBinder().unlinkToDeath(this.mDeathRecipient, 0);
this.mProxy = null;
this.mApplication.unbindService(mServiceConnection);
}
}
public void setStateListener(IServiceConnectListener listener) {
SdkLogUtils.logV(TAG, "[setStateListener]" + listener);
mServiceListener = listener;
}
public void removeStateListener() {
SdkLogUtils.logV(TAG, "[removeStateListener]");
mServiceListener = null;
}
protected T getProxy() {
return mProxy;
}
protected LinkedBlockingQueue getTaskQueue() {
return mTaskQueue;
}
public Handler getMainHandler() {
return mMainThread;
}
protected abstract String getServicePkgName();
protected abstract String getServiceClassName();
protected String getServiceAction() {
return null;
}
protected abstract T asInterface(IBinder service);
protected abstract long getRetryBindTimeMill();
}
封装 SDK
开发中多数时候我们只有一个用于操作Service Interface，如下所示：
interface HvacInterface {
oneway void setTemperature(int temperature);
oneway void requestTemperature();
boolean registerCallback(in HvacCallback callback);
boolean unregisterCallback(in HvacCallback callback);
}
用于回调Server端处理结果的Callback
interface HvacCallback {
oneway void onTemperatureChanged(double temperature);
}
基于BaseConnectManager封装一个HvacManager
public class HvacManager extends BaseConnectManager {
private static final String TAG = SdkLogUtils.TAG_FWK + HvacManager.class.getSimpleName();
private static volatile HvacManager sHvacManager;
public static final String SERVICE_PACKAGE = "com.fwk.service";
public static final String SERVICE_CLASSNAME = "com.fwk.service.SimpleService";
private static final long RETRY_TIME = 5000L;
private final List mCallbacks = new ArrayList<>();
private final HvacCallback.Stub mSampleCallback = new HvacCallback.Stub() {
@Override
public void onTemperatureChanged(double temperature) throws RemoteException {
SdkLogUtils.logV(TAG, "[onTemperatureChanged] " + temperature);
getMainHandler().post(() -> {
for (IHvacCallback callback : mCallbacks) {
callback.onTemperatureChanged(temperature);
}
});
}
};
public static HvacManager getInstance() {
if (sHvacManager == null) {
synchronized (HvacManager.class) {
if (sHvacManager == null) {
sHvacManager = new HvacManager();
}
}
}
return sHvacManager;
}
@Override
protected String getServicePkgName() {
return SERVICE_PACKAGE;
}
@Override
protected String getServiceClassName() {
return SERVICE_CLASSNAME;
}
@Override
protected HvacInterface asInterface(IBinder service) {
return HvacInterface.Stub.asInterface(service);
}
@Override
protected long getRetryBindTimeMill() {
return RETRY_TIME;
}
/******************/
public void requestTemperature() {
Remote.tryExec(() -> {
if (isServiceConnected(true)) {
getProxy().requestTemperature();
} else {
// 将此方法放入队列中，等Service重新连接后，会依次调用
getTaskQueue().offer(this::requestTemperature);
}
});
}
public void setTemperature(int temperature) {
Remote.tryExec(() -> {
if (isServiceConnected(true)) {
getProxy().requestTemperature();
} else {
getTaskQueue().offer(() -> {
setTemperature(temperature);
});
}
});
}
public boolean registerCallback(IHvacCallback callback) {
return Remote.exec(() -> {
if (isServiceConnected(true)) {
boolean result = getProxy().registerCallback(mSampleCallback);
if (result) {
mCallbacks.remove(callback);
mCallbacks.add(callback);
}
return result;
} else {
getTaskQueue().offer(() -> {
registerCallback(callback);
});
return false;
}
});
}
public boolean unregisterCallback(IHvacCallback callback) {
return Remote.exec(() -> {
if (isServiceConnected(true)) {
boolean result = getProxy().unregisterCallback(mSampleCallback);
if (result) {
mCallbacks.remove(callback);
}
return result;
} else {
getTaskQueue().offer(() -> {
unregisterCallback(callback);
});
return false;
}
});
}
}
上述代码中，我们需要注意一点，每次调用远程方法都需要判断当前service是否处于连接，如果与Service的连接被断开了，我们要把方法放入一个队列中去，当Service重新被绑定上后，队列中的方法，会依次被取出执行。
最后，我们在SDK module的 build.gradle中加入可以编译出jar的脚本
// makeJar
def zipFile = file('build/intermediates/aar_main_jar/release/classes.jar')
task makeJar(type: Jar) {
from zipTree(zipFile)
archiveBaseName = "sdk"
destinationDirectory = file("build/outputs/")
manifest {
attributes(
'Implementation-Title': "${project.name}",
'Built-Date': new Date().getDateTimeString(),
'Built-With':
"gradle-${project.getGradle().getGradleVersion()},groovy-${GroovySystem.getVersion()}",
'Created-By':
'Java ' + System.getProperty('java.version') + ' (' + System.getProperty('java.vendor') + ')')
}
}
makeJar.dependsOn(build)
使用示例
public void requestTemperature() {
LogUtils.logI(TAG, "[requestTemperature]");
HvacManager.getInstance().requestTemperature();
}
实际使用时，调用方既不需要关心Service的绑定状态，也不需要主动进行线程切换，极大的简便了HMI的开发。
本文源码地址： https://github.com/linux-link/CarServerArch
参考资料
Android 接口定义语言 (AIDL) | Android 开发者 | Android Developers