# Key Concepts

In the following use case sections, we will guide you through the most common usage scenarios and reveal tips and easy-to-understand guidelines to help you get the most out of the HERE SDK for Android.

## How to use this Guide?

You can read this guide in any order. All sections are independent from each other, making it easy to skip any section and to dive straight into the topics which you are most interested in.

• In the example section, you can find the example apps accompanying this user guide.
• If you are interested in building your first app showing a HERE map, take a look at the Get Started section to guide you through the first simple steps.
• See an overview of the available use cases covered in this Developer's Guide.

## Conventions

For this guide, we preferably avoid the use of lambda notations to show the full type of information and other details, such as callback or listener name. Since Android Studio supports one-click conversion between anonymous classes and lambdas, adapting the examples to suit your personal preference should be simple.

### Dispose Objects

All HERE SDK classes will be garbage collected by Android if the instance is no longer referenced or set to null.

For the SDKNativeEngine, which can be initialized automatically or programmatically, you can free resources by calling SDKNativeEngine.getSharedInstance().dispose(), for example, when the hosting activity's lifetime has ended. Calling dispose() will stop pending requests and close open files and databases that are still running on the main thread. After calling dispose() any related HERE SDK feature should no longer be used.

### Callbacks and Listeners

• The HERE SDK exposes callbacks for single event notification such as for search results.
• For reoccurring event notifications such as for gesture events, listeners are used. When multiple listeners can be set, then the method pattern add_x() and remove_x() is used as naming convention. If only one listener can be set at a time, the property pattern is used. Set a listener property to null to stop listening.

### Debug Logs

You can use the LogAppender interface to insert your own log class into the SDKNativeEngine. This way you can log HERE SDK messages for various predefined log levels even for release builds of your app.

### Code Snippets

The shown code snippets cover best practice example code ready to be used for your own applications. However, for the sake of simplicity and to not shadow the educational approach of this guide, not all edge scenarios may be handled, especially when it comes to error handling or robust threading. In some cases, the obvious code is left out, but it can be found in the accompanying example apps that can be built and deployed instantly on any supported device with a set of valid HERE credentials.

### Design Principles

The accompanying example apps follow the same structure. As much as possible the HERE SDK example code is decoupled from the surrounding platform code. We hope this makes it easier to see the relevant parts of the shown APIs. Each example app follows the same entry point from which the HERE SDK is initialized. Since each app is focusing on a different aspect of the HERE SDK, that code can be found in a single class postfixed with "...Example.java" in its class name. Most often this class gets a reference to a MapView to start its work.

Following the popular POJO (PLain-Old-Java-Object) principle, the example code is kept free of most Android dependencies - instead it's mostly pure Java code that shows how the HERE SDK can be used.

### Dependency Management

Currently, dependency management, for example, via Gradle, is not yet supported. This means that the HERE SDK AAR binary must be copied locally to an application project as described in the Get Started section.

## Is the HERE SDK Thread Safe?

The HERE SDK is not guaranteed to be thread safe and it is recommended to make calls to the SDK from the main thread. Internally, the HERE SDK will offload most of its work to a background thread, but callbacks to your code will always occur on the main thread. In general, thread safety is the responsibility of the caller. For example, it is unsafe to reuse an engine on different threads unless your code is synchronized.

### Use TaskHandles to Cancel Asynchronous Operations

Most asynchronous methods provide a TaskHandle as immediate return value, while the final result of the operation will be returned in a completion handler with a delay. The TaskHandle provides status information and it allows to abort an ongoing operation.

## Unit Tests

It's easy to write unit tests for your app logic that uses the HERE SDK as all classes are fully mockable. Inside the release package you can find a heresdk-mock JAR file that enables mocking of all HERE SDK classes. Below you can see an example using Mockito. This will also work with most other frameworks that allow to create mocked objects:

@RunWith(MockitoJUnitRunner.class)
public class TestExample {

@Test
public void testNonStaticMethod() {
Angle angleMock = mock(Angle.class);

when(angleMock.getDegrees()).thenReturn(10.0);

assertEquals(10.0, angleMock.getDegrees());
verify(angleMock, times(1)).getDegrees();
verifyNoMoreInteractions(angleMock);
}

...
}


Use the following dependency in your app's build.gradle setup:

def getHereSdkArtefactName() {
def aarFile = fileTree(dir: 'libs', include: ['heresdk-*.aar']).first()
// Filename without extension is necessary.
return org.apache.commons.io.FilenameUtils.getBaseName(aarFile.name)
}

// Exclude HERE SDK's aar from unit test's dependencies.
configurations.testImplementation {
exclude module: getHereSdkArtefactName()
}

dependencies {
implementation(name: getHereSdkArtefactName(), ext:'aar')

implementation 'com.android.support:appcompat-v7:28.0.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'

// Keep in mind that the original HERE SDK aar must be excluded from
// the test dependency, see above.
testImplementation fileTree(dir: 'libs', include: ['*mock*.jar'])
testImplementation 'junit:junit:4.12'
testImplementation 'org.mockito:mockito-core:3.1.0'
}


With this setup your app will use the mock JAR when executing unit tests and the real HERE SDK AAR when building the app. Place the heresdk-edition-mock-version.jar into the same app/libs folder as the heresdk-edition-version.aar.

Check the UnitTesting example app to find more use case examples.

## Coverage

Consult the coverage page to get detailed information on supported countries and languages per feature.

## Defining a Scope

Optionally, you can define several scopes for an application - for example, to define a debugScope for testing your app. For a production version of your app, you may decide to leave the scope just empty, which is the default value. See the IAM Guide for more details on how to set up a project ID.

Each app belongs at least to one project. In the Projects Manager via your HERE platform account, select Projects: This allows you to see the available project IDs. You can also add more. Each project ID shows a HRN value.

Set the HRN value as scope in your AndroidManifest file as follows:

<!-- optionally set a project scope if needed -->
<meta-data
android:name="com.here.sdk.access_scope"
android:value="YOUR_PROJECT_SCOPE" />


Note that a project ID must be unique and cannot be changed for the lifetime of the organization's account. Project IDs must be between 4 and 16 characters in length. They affect also the HRN value. If the scope/HRN is set by an application, it will be used for authentication and the internal token creation of an application. If an unknown scope is set, any authentication attempt would fail and the application logs would indicate this.

## Engines

The HERE SDK contains several modules - or engines as we call them - to execute specific tasks such as calculating a route with the RoutingEngine or requesting search results via the SearchEngine. There are many more engines you can use with the HERE SDK and you can read more about them in the dedicated chapters below. However, most engines share common concepts that makes it easier to use them. For example:

• All engines share similar interfaces, callbacks and error handling.
• It is possible to start multiple instances of an engine in parallel.
• An online connection is required.

## Initialize the HERE SDK

By default, the HERE SDK is initialized at application start. This is done using a ContentProvider, even before a MapView is shown. To change this behavior, you can manually initialize the HERE SDK, for example, to defer initialization at a later point in time. For this you need to add an entry to the AndroidManifest file to disable the HERE SDK's InitProvider. See below for more details.

• If your app immediately wants to show a map view after app start, then for most use cases it's sufficient to follow the Get Started guide - and the HERE SDK will be automatically initialized together with the map view. However:
• If your app needs to show a map view at a later point in time or if a fast loading time is critical for you, consider to manually initialize the HERE SDK.
• Note: Depending on your contractual details, the time of initialization may have an impact on how transactions and monthly active users (MAU) are counted.

Below you can see how to manually initialize the HERE SDK. This also allows to inject credentials programmatically - together with other initialization options.

### Set HERE Credentials from Manifest or Programmatically

All HERE SDK engines, except for SDKNativeEngine, can operate independently from each other and require HERE credentials to request data. The credentials can be set in the AndroidManifest file as shown in the Get Started guide - or programmatically. This can be useful, for example, to inject credentials at runtime from a web service.

By default, when using a map view in your app, the HERE SDK is initialized automatically and it is reading the credentials from the manifest. In addition, a default cache path is used for caching map data.

### Note

The HERE SDK does not verify credentials at instantiation time. This only happens once a feature is used that requires authentification. In case of a failure, you will get with a dedicated error message. For example, the SearchEngine will reply with a SearchError.AUTHENTIFICATION_FAILED error. Other engines provide similar error codes.

Freemium credentials will work for most features, but not for features like offline maps which are exclusive for editions such as the Navigate Edition. If the credentials are invalid, the logs contain "[ERROR]" messages with a text similar to "Failed to get the authentication token: Authentication failed, error code: 1". This indicates that the credentials are not accepted when using a service. If you want to ensure that your credentials are set up correctly, use a premium feature with a specialized engine and check if the engine replies with an error value.

### Use SDKOptions to Set HERE Credentials and Cache Path

When you want to set the credentials programmatically, you need to create your own instance of the SDKNativeEngine, which can then be used to set or to change your HERE SDK credentials at runtime:

// Optionally, clear a previous instance (if any).
SDKNativeEngine.getSharedInstance().dispose();

SDKOptions sdkOptions = new SDKOptions("YOUR_ACCESS_KEY_ID", "YOUR_ACCESS_KEY_SECRET", "");

SDKNativeEngine sdkNativeEngine = null;
try {
sdkNativeEngine = new SDKNativeEngine(sdkOptions);
} catch (InstantiationErrorException e) {
// Handle exception.
}

SDKNativeEngine.setSharedInstance(sdkNativeEngine);

try {
SearchEngine searchEngine = new SearchEngine();
// ...
} catch (InstantiationErrorException e) {
// Handle exception.
}


This allows you to set a shared instance that will be used for all engines under the hood. Above, we initialize the SearchEngine as an example. Note that a shared instance is also required when you add a map view.

By setting an empty string as cache path, you keep the default cache path - which is also accessible via context.getCacheDir().getPath() or SDKNativeEngine.getSharedInstance().getOptions().cachePath.

### Note

Note: It is also possible to specify the cache path from the AndroidManifest file. Consult the API Reference for the SDKNativeEngine to see an example.

Multiple SDKNativeEngine instances can’t have the same access key id and the cache path is ensured to be unique per access key id. After creating a new SDKNativeEngine, the access key id cannot be changed. Only the secret key can be changed afterwards.

In general, it should not be necessary to initialize the HERE SDK multiple times and only one sharedInstance can be set.

Alternatively, in rare use cases it may be useful to set an individual SDKNativeEngine instance for each of the feature engines:

SearchEngine searchEngine = new SearchEngine(sdkNativeEngine);


By default, the InitProvider of the HERE SDK will look for the credentials in your AndroidManifest file. Therefore, when setting credentials programmatically, keep the tags holding dummy values for id and secret, like shown in the snippet below. Empty values will lead to an exception:

<meta-data android:name="com.here.sdk.access_key_id" android:value="cdefgabc" />
<meta-data android:name="com.here.sdk.access_key_secret" android:value="cdefgabc" />


Alternatively, call InitProvider.initialize(appContext) to avoid that the SDKInitializer will look into the AndroidManifest file - this procedure is described in the next section.

### Manually Initialize the HERE SDK

When you want to set credentials programmatically and you want to avoid keeping meta-data tags in the manifest (see above), you can disable the HERE SDK's InitProvider and manually initialize the HERE SDK.

The InitProvider is responsible for the initialization of the HERE SDK and it reads the credentials from the manifest file. If it cannot find the <meta-data>-tag that is supposed to hold the credentials, it will throw a MetaDataNotFoundException.

To disable the InitProvider, add a new <provider> tag to the app's manifest nested under the <application>-tag. As name/authorities, specify the InitProvider. Disable it by setting tools:node="remove":

<provider
android:name="com.here.sdk.engine.InitProvider"
android:authorities="com.here.sdk.engine.InitProvider"
android:exported="false"
tools:node="remove" />


For this, you also need to bind the tools namespace declaration to the manifest tag as follows:

<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="com.your_domain.your_app">


Finally, after the InitProvider has been disabled, you need to call InitProvider.initialize(appContext) to initialize the required platform modules. Make sure to call this before creating the SDKNativeEngine - and before setting the content view holding your map view (if your app contains a map view):

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

// Optionally, clear a previous instance (if any).
SDKNativeEngine.getSharedInstance().dispose();

// Manually initialize the HERE SDK.
InitProvider.initialize(appContext);

// Specify credentials programmatically and keep default cache path by setting an empty string.
SDKOptions sdkOptions = new SDKOptions("YOUR_ACCESS_KEY_ID", "YOUR_ACCESS_KEY_SECRET", "");

SDKNativeEngine sdkNativeEngine = null;
try {
sdkNativeEngine = new SDKNativeEngine(sdkOptions);
} catch (InstantiationErrorException e) {
// Handle exception.
}

SDKNativeEngine.setSharedInstance(sdkNativeEngine);

setContentView(R.layout.activity_main);

// Get a MapView instance from the layout.
mapView = findViewById(R.id.map_view);
mapView.onCreate(savedInstanceState);

// Handle required Android permissions ...
}


This way, you can manually initialize the HERE SDK and avoid setting dummy credentials in your manifest file.

If you don't set your credentials programmatically, the HERE SDK will be initialized automatically using the values found in the manifest. Either way, invalid credentials will not block execution until these credentials are used to authenticate your app when you start to use an engine to request data - or when you want to show a map view.

Tip: One option to keep credentials secure is to store them on a secure server and retrieve them by requests using SSL connections. Credentials stored in AndroidManifest are easy to unveil, a better option can be to use data protection mechanisms.

For best practice, consider:

• To avoid keeping sensitive data in plain text.
• To transfer credentials using a secure communication channel.
• To store credentials using device security mechanisms and strong encryption ciphers.
• To add anti-tampering and anti-debugging code, so that a potential attacker cannot intercept data during dynamic runtime execution.
• Track the application usage to detect anomalies.

### Use Engines with or without a Map View

Engines do not need a map view to operate. Therefore it is possible to run an engine as a stand-alone, without any map view added to your application. This way, you can build an app solely around a specific engine. With or without a map view - the procedure to create a new engine is exactly the same:

try {
searchEngine = new SearchEngine();
} catch (InstantiationErrorException e) {
// Handle exception.
}


When you use the default constructor to initialize an engine for a stand-alone usage, the HERE SDK will use a shared SDKNativeEngine under the hood to take the credentials as found in the AndroidManifest file. Alternatively, you can provide the credentials programmatically as shown in the previous section.

### Note

It is not possible to initialize an engine during the Application's onCreate() lifecycle. Any other point in time is fine. For example, a good place to initialize an engine may be in an Activity's onCreate()-method.