Integration Basics
How SDL Works
SmartDeviceLink works by sending remote procedure calls (RPCs) back and forth between a smartphone application and the SDL Core. These RPCs allow you to build the user interface, detect button presses, play audio, and get vehicle data, among other things. You will use the SDL library to build your app on the SDL Core.
In this guide, we exclusively use Android Studio. We are going to set-up a bare-bones application so you get started using SDL.
SmartDeviceLink Service
A SmartDeviceLink Service should be created to manage the lifecycle of the SDL session. The SdlService should build and start an instance of the SdlManager which will automatically connect with a headunit when available. This SdlManager will handle sending and receiving messages to and from SDL after it is connected.
Create a new service and name it appropriately, for this guide we are going to call it SdlService.
public class SdlService extends Service { //... }
If you created the service using the Android Studio template then the service should have been added to your AndroidManifest.xml. If not, then service needs to be defined in the manifest:
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.company.mySdlApplication"> <application> <service android:name=".SdlService" android:enabled="true"/> </application> </manifest>
Entering the Foreground
Because of Android Oreo's requirements, it is mandatory that services enter the foreground for long running tasks. The first bit of integration is ensuring that happens in the onCreate method of the SdlService or similar. Within the service that implements the SDL lifecycle you will need to add a call to start the service in the foreground. This will include creating a notification to sit in the status bar tray. This information and icons should be relevant for what the service is doing/going to do. If you already start your service in the foreground, you can ignore this section.
public void onCreate() { super.onCreate(); //... if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) { NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE); notificationManager.createNotificationChannel(...); Notification serviceNotification = new Notification.Builder(this, *Notification Channel*) .setContentTitle(...) .setSmallIcon(....) .setLargeIcon(...) .setContentText(...) .setChannelId(channel.getId()) .build(); startForeground(id, serviceNotification); } }
Note
The sample code checks if the OS is of Android Oreo or newer to start a foreground service. It is up to the app developer if they wish to start the notification in previous versions.
Exiting the Foreground
It's important that you don't leave your notification in the notification tray as it is very confusing to users. So in the onDestroy method in your service, simply call the stopForeground method.
@Override public void onDestroy(){ //... if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.O){ NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE); if(notificationManager!=null){ //If this is the only notification on your channel notificationManager.deleteNotificationChannel(* Notification Channel*); } stopForeground(true); } }
Implementing SDL Manager
In order to correctly connect to an SDL enabled head unit developers need to implement methods for the proper creation and disposing of an SdlManager in our SdlService.
Note
An instance of SdlManager cannot be reused after it is closed and properly disposed of. Instead, a new instance must be created. Only one instance of SdlManager should be in use at any given time.
public class SdlService extends Service { //The manager handles communication between the application and SDL private SdlManager sdlManager = null; //... @Override public int onStartCommand(Intent intent, int flags, int startId) { if (sdlManager == null) { MultiplexTransportConfig transport = new MultiplexTransportConfig(this, APP_ID, MultiplexTransportConfig.FLAG_MULTI_SECURITY_OFF); // The app type to be used Vector<AppHMIType> appType = new Vector<>(); appType.add(AppHMIType.MEDIA); // The manager listener helps you know when certain events that pertain to the SDL Manager happen SdlManagerListener listener = new SdlManagerListener() { @Override public void onStart() { // After this callback is triggered the SdlManager can be used to interact with the connected SDL session (updating the display, sending RPCs, etc) } @Override public void onDestroy() { SdlService.this.stopSelf(); } @Override public void onError(String info, Exception e) { } }; // Create App Icon, this is set in the SdlManager builder SdlArtwork appIcon = new SdlArtwork(ICON_FILENAME, FileType.GRAPHIC_PNG, R.mipmap.ic_launcher, true); // The manager builder sets options for your session SdlManager.Builder builder = new SdlManager.Builder(this, APP_ID, APP_NAME, listener); builder.setAppTypes(appType); builder.setTransportType(transport); builder.setAppIcon(appIcon); sdlManager = builder.build(); sdlManager.start(); } }
The onDestroy() method from the SdlManagerListener is called whenever the manager detects some disconnect in the connection, whether initiated by the app, by SDL, or by the device’s connection.
Note
The sdlManager must be shutdown properly in the SdlService.onDestroy() callback using the method sdlManager.dispose().
Determining SDL Support
You have the ability to determine a minimum SDL protocol and a minimum SDL RPC version that your app supports. We recommend not setting these values until your app is ready for production. The OEMs you support will help you configure the correct minimumProtocolVersion and minimumRPCVersion during the application review process.
If a head unit is blocked by protocol version, your app icon will never appear on the head unit's screen. If you configure your app to block by RPC version, it will appear and then quickly disappear. So while blocking with minimumProtocolVersion is preferable, minimumRPCVersion allows you more granular control over which RPCs will be present.
builder.setMinimumProtocolVersion(new Version("3.0.0")); builder.setMinimumRPCVersion(new Version("4.0.0"));
Listening for RPC notifications and events
We can listen for specific events using SdlManager's builder setRPCNotificationListeners. The following example shows how to listen for HMI Status notifications. Additional listeners can be added for specific RPCs by using their corresponding FunctionID in place of the ON_HMI_STATUS in the following example and casting the RPCNotification object to the correct type.
Example of a listener for HMI Status:
Map<FunctionID, OnRPCNotificationListener> onRPCNotificationListenerMap = new HashMap<>(); onRPCNotificationListenerMap.put(FunctionID.ON_HMI_STATUS, new OnRPCNotificationListener() { @Override public void onNotified(RPCNotification notification) { OnHMIStatus onHMIStatus = (OnHMIStatus) notification; if (onHMIStatus.getHmiLevel() == HMILevel.HMI_FULL && onHMIStatus.getFirstRun()){ // first time in HMI Full } } }); builder.setRPCNotificationListeners(onRPCNotificationListenerMap);
SmartDeviceLink Router Service
The SdlRouterService will listen for a connection with an SDL enabled module. When a connection happens, it will alert all SDL enabled apps that a connection has been established and they should start their SDL services.
We must implement a local copy of the SdlRouterService into our project. The class doesn't need any modification, it's just important that we include it. We will extend the com.smartdevicelink.transport.SdlRouterService in our class named SdlRouterService:
Note
Do not include an import for com.smartdevicelink.transport.SdlRouterService. Otherwise, we will get an error for 'SdlRouterService' is already defined in this compilation unit.
public class SdlRouterService extends com.smartdevicelink.transport.SdlRouterService { //Nothing to do here }
Must
The local extension of the com.smartdevicelink.transport.SdlRouterService must be named SdlRouterService.
Must
Make sure this local class SdlRouterService.java is in the same package of SdlReceiver.java (described below)
If you created the service using the Android Studio template then the service should have been added to your AndroidManifest.xml otherwise the service needs to be added in the manifest. Because we want our service to be seen by other SDL enabled apps, we need to set android:exported="true". The system may issue a lint warning because of this, so we can suppress that using tools:ignore="ExportedService".
Must
The SdlRouterService must be placed in a separate process with the name com.smartdevicelink.router. If it is not in that process during it's start up it will stop itself.
Intent Filter
<intent-filter> <action android:name="com.smartdevicelink.router.service"/> </intent-filter>
The new versions of the SDL Android library rely on the com.smartdevicelink.router.service action to query SDL enabled apps that host router services. This allows the library to determine which router service to start.
Must
This intent-filter MUST be included.
Metadata
Router Service Version
<meta-data android:name="sdl_router_version" android:value="@integer/sdl_router_service_version_value" />
Adding the sdl_router_version metadata allows the library to know the version of the router service that the app is using. This makes it simpler for the library to choose the newest router service when multiple router services are available.
Custom Router Service
<meta-data android:name="sdl_custom_router" android:value="false" />
Note
This is only for specific OEM applications, therefore normal developers do not need to worry about this.
Some OEMs choose to implement custom router services. Setting the sdl_custom_router metadata value to true means that the app is using something custom over the default router service that is included in the SDL Android library. Do not include this meta-data entry unless you know what you are doing.
SmartDeviceLink Broadcast Receiver
The Android implementation of the SdlManager relies heavily on the OS's bluetooth and USB intents. When the phone is connected to SDL and the router service has sent a connection intent, the app needs to create an SdlManager, which will bind to the already connected router service. As mentioned previously, the SdlManager cannot be re-used. When a disconnect between the app and SDL occurs, the current SdlManager must be disposed of and a new one created.
The SDL Android library has a custom broadcast receiver named SdlBroadcastReceiver that should be used as the base for your BroadcastReceiver. It is a child class of Android's BroadcastReceiver so all normal flow and attributes will be available. Two abstract methods will be automatically populate the class, we will fill them out soon.
Create a new SdlBroadcastReceiver and name it appropriately, for this guide we are going to call it SdlReceiver:
public class SdlReceiver extends SdlBroadcastReceiver { @Override public void onSdlEnabled(Context context, Intent intent) { //... } @Override public Class<? extends SdlRouterService> defineLocalSdlRouterClass() { //... } }
Must
SdlBroadcastReceiver must call super if onReceive is overridden
@Override public void onReceive(Context context, Intent intent) { super.onReceive(context, intent); //your code here }
If you created the BroadcastReceiver using the Android Studio template then the service should have been added to your AndroidManifest.xml otherwise the receiver needs to be defined in the manifest. Regardless, the manifest needs to be edited so that the SdlBroadcastReceiver needs to respond to the following intents:
- android.bluetooth.device.action.ACL_CONNECTED
- sdl.router.startservice
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.company.mySdlApplication"> <application> <receiver android:name=".SdlReceiver" android:exported="true" android:enabled="true"> <intent-filter> <action android:name="android.bluetooth.device.action.ACL_CONNECTED" /> <action android:name="sdl.router.startservice" /> </intent-filter> </receiver> </application> </manifest>
Note
The intent sdl.router.startservice is a custom intent that will come from the SdlRouterService to tell us that we have just connected to an SDL enabled piece of hardware.
Must
SdlBroadcastReceiver has to be exported, or it will not work correctly
Next, we want to make sure we supply our instance of the SdlBroadcastService with our local copy of the SdlRouterService. We do this by simply returning the class object in the method defineLocalSdlRouterClass:
public class SdlReceiver extends SdlBroadcastReceiver { @Override public void onSdlEnabled(Context context, Intent intent) { } @Override public Class<? extends SdlRouterService> defineLocalSdlRouterClass() { //Return a local copy of the SdlRouterService located in your project return com.company.mySdlApplication.SdlRouterService.class; } }
We want to start the SdlManager when an SDL connection is made via the SdlRouterService. We do this by taking action in the onSdlEnabled method:
Must
Apps must start their service in the foreground as of Android Oreo (API 26).
public class SdlReceiver extends SdlBroadcastReceiver { @Override public void onSdlEnabled(Context context, Intent intent) { //Use the provided intent but set the class to the SdlService intent.setClass(context, SdlService.class); if(Build.VERSION.SDK_INT < Build.VERSION_CODES.O) { context.startService(intent); }else{ context.startForegroundService(intent); } } @Override public Class<? extends SdlRouterService> defineLocalSdlRouterClass() { //Return a local copy of the SdlRouterService located in your project return com.company.mySdlApplication.SdlRouterService.class; } }
Note
The onSdlEnabled method will be the main start point for our SDL connection session. We define exactly what we want to happen when we find out we are connected to SDL enabled hardware.
Main Activity
Now that the basic connection infrastructure is in place, we should add methods to start the SdlService when our application starts. In onCreate() in your main activity, you need to call a method that will check to see if there is currently an SDL connection made. If there is one, the onSdlEnabled method will be called and we will follow the flow we already set up:
public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); //If we are connected to a module we want to start our SdlService SdlReceiver.queryForConnectedService(this); } }