a gps location plotting android application - codeproject

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Rate this:Raja.D.Singh, 9 Oct 2013 CPOL

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A GPS Location Plotting Android Application

Develop an Android application that plots user location on a map continuously.

IntroductionRecently, I was tasked with writing an application that heavily relied on GPS and mapping of custom hardwaredevices that were built with locationaware components. Even though I have been using Eclipse for these tasksfor quite some time, Android Studio's glittering new features and ease of use caught my attention to try it outfor the task. During the few weeks I had worked with Android Studio and with Google Maps Android API V2, Ilearned some lessons that are worth sharing, so that others need not reinvent the wheel and avoid the knownpitfalls on their quest.

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In this article, we will try to focus on developing an Android application that uses Google Maps Android APIV2, using Android Studio IDE. Very recently Google deprecated and as of March 18th, 2013, stopped issuingAPI keys for Google Maps Android V1 and started recommending V2. A lot of documentation, books andother resources on the web discuss doing things that are centered around V1 and it is daunting for a newcomer to sieve through all that and get some useful information on developing applications using API V2. Toadd to the confusion, there is not very many resources on the web that discusses using Android Studio forsuch development. Let us hope to fill that gap here.

BackgroundGoogle announced on May 16th, 2013, at their Google I/O conference, Android Studio as their IntegratedDevelopment Environment, IDE, of choice to develop Android Applications. Android Studio is essentiallyInettliJ IDEA from JetBrains, but is heavily focused on the development of Android applications. Android Studiouses Gradle for dependency resolution and most of the project management tasks in the IDE. Android Studiois available for download from here.. Android Studio has an automatic software updater that automaticallychecks for new updates and updates the IDE to the latest version. As of this writing, the newest version was0.2.11, Build AI132.855830.

Prior to Android Studio and even after, majority of developers use Eclipse as a fundamental platform forAndroid application development. Eclipse is an excellent platform that provides a great IDE for softwaredevelopment in Java, C++ and various other languages.

Create an Android applicationI am going to assume that the reader is familiar with the structure of an Android Application and the filesinvolved in making an application, in addition to the concepts of Activity, Intent, Activity life cycle and variousstates of it during its existence, Resource files and Strings etc. There are many books and text available off theweb on Android Application development concepts. We are going to focus on a specific application with aspecific tool in this article. I have used a Linux machine with Android Studio. The information in this articlecould be used effectively for a Windows or Mac machine running same version of Android Studio. Let's dive in.

Android Studio creates a skeletal application when you chose New Project from the initial screen, whenstarted. You are presented with a dialog as shown below. Fill in the Name of the application with anymeaningful name such as GPSPlotter, in this example. Fill in the package name for your code, such ascom.siriusmicrotech.gpsplotter, in this example. This will be the application name that is going to be used forAPI Key generation that we discuss later in the article. Please note that the Minimum required SDK is selectedas AP11, since Google Maps Android API V2 requires SDK greater than AP8 for it to work. Then click next toaccept all the defaults through the subsequent screen presented until the project is created by clicking onFinish.



Here is the screen shot of the skeletal project we have created.

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Even though there are many files created in this process, luckily, we are going to focus on only the followingfive files:

MainActivity.javaactivity_main.xmlstrings.xmlAndroidManifest.xmlbuild.gradle

Location ProvidersBefore we start to modify these files, let us discuss some background on why we do what we do in thefollowing sections. Android devices are equipped with GPS hardware. Android provides a very straight forwardAPI to access Location information derived from GPS hardware along with WiFi and Cellular networkconnection sources that helps provide location information. Since an application should be able to access thecurrent location information of the device, we need to get the users permission for the application to accessthis service during installation. During debugging, the application is given permission to access these services,without prompting the user to acknowledge. The following section sets up various permissions for theapplication to access such as accessing internet, since Maps are to be downloaded from Internet, accessingStorage, since Maps need to be cached and for accessing Location providers such as GPS and other forms oflocation services. Android Maps also needs OpenGL. Here are the lines added to our AndroidManifest.xml filejust above the tag.

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Using Google Maps Android API V2 in our CodeSince Google Maps Android API V2 is not included in the Android Development Kit ADK and instead it isincluded in the Google Play Services API, we need to install it separately. Fire up SDK manager and go to theExtras section and check against the Google Play Services and Google Repository and click Install Packages.



Once Google Play Services API is installed, we need to include it in our project. The very nice tutorial atGoogle's android developer site is written targeting Eclipse as the platform, it suggests including a referenceto the Google Services Library by Importing it into the workspace. This will not work with Android Studio sinceGradle is used for dependency resolution here. So, we need to edit build.gradle file as follows, by adding asingle line in the dependency section of it. Please note, as of this writing, the UI can not be used to add thisdependency for Gradle. The only way is to edit the build.gradle file manually. However, one must realize thatthis is much simpler than the solution discussed at the developer's site.

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dependencies{//GooglePlayServicescompile'com.google.android.gms:playservices:3.2.65'//SupportLibrarycompile'com.android.support:appcompatv7:18.0.0'}

Now, to show a map in our application, we need a Fragment in our layout. This is done by replacing theTextView section in the activity_main.xml file with a Fragment section as follows:

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android:layout_width="match_parent"android:layout_height="match_parent"/>

And modifying MainActivity.java by deriving the MainActivity class from FragmentActivity instead ofActivity, as follows:

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publicclassMainActivityextendsFragmentActivity

Now, technically we have everything on the device side of the application. However, the Map has to comefrom the Cloud. To access the Maps from the cloud, we need a special authentication key called API Key, givento our application by the Google Cloud services, where the Maps are served from. Even though it sounds verycomplicated, it is very straight forward to obtain this key by following the instructions given here

Please note that for our purposes, we can use our debug certificate to obtain our API Key. A release certificateshould be used for generating this key, only if we are going to publish the application. Once this key isobtained, copy this key into the AndroidManifest.xml file as follows, just above tag.

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Please note, it is much simpler to connect an Android device to the PC and install this application on it andtest it than to use the Emulator. However, please remember to enable USB debugging on the device. If yourdevice is running Jelly Bean, by default, Developer Options section of the Settings menu is hidden to protectthe user from doing any harm with this feature. Go to System Settings Menu and scroll all the way down to seeif you see Developer Options listed. If it is not listed, to bring the Developer Options to view, select AboutPhone menu and scroll all the way down where you see Build Number. Keep tapping on Build Number severaltimes rapidly until you see that Developer Options are enabled. Go into Developer Options menu and enableUSB debugging by clicking on the check mark against it.

Connect your device to the PC with the USB cable and hit run on the Android Studio Menu. If everything wentwell, you would see a Google map displayed centered somewhere around the continent of Africa! That's notmuch work, is it.

Displaying and following our location on the MapDisplaying a map of the world is not very exciting unless we are able to trace our location on it somehow.Now, let us start using our location services that our application has already applied for permission in theAndroidManifest.xml file earlier on. The GoogleMap class provides a neat integration many features, includinglocation tracking. So, the sequence of tasks here are to

get the object reference for the map we just displayedtie up a location listener to this map that responds to location changed events from the locationservicesfocus our location on the map



We can obtain the map object reference by getting the reference to the Fragment that we inserted in thelayout file as follows:

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myMap=((SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.map)).getMap();

Now, to mark our location on the map, with a blue arrow icon, we enable the feature in our map object asfollows. Note, we check for null since the map may not be available before it is rendered completely.

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if(myMap!=null){myMap.setMyLocationEnabled(true);}

Since we now have the object reference for the map, we can now start to listen to the location updates fromlocation services. The recommended method for doing this is to setup a location client for the locationservices within our Main Activity with the following code

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myLocationClient=newLocationClient(getApplicationContext(),this,this);//oncewehavethereferencetotheclient,connectitif(myLocationClient!=null)myLocationClient.connect();

The LocationClient object constructor takes three parameters, the first is the application context and thesecond is the object that implements Connection callbacks, such as establishment of connection andDisconnection, and the third is the object that implements Connection failure listener. Since we pass thereference to the MainActivity object as the two call back inputs, we have to implement those methods inour MainActivity class. Once we modify our MainActivity class definition line as follows to implementthose two interfaces and the LocationListener interface. Android Studio will prompt us to implement therequired methods and will automatically populate our class with the methods.

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publicclassShowMeOnMapextendsFragmentActivityimplementsGooglePlayServicesClient.ConnectionCallbacks,GooglePlayServicesClient.OnConnectionFailedListener,com.google.android.gms.location.LocationListener{

The following are the methods that are populated by Android Studio to implement those three interfaces:

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@OverridepublicvoidonConnected(Bundlebundle){}

@OverridepublicvoidonDisconnected(){

}

@OverridepublicvoidonLocationChanged(Locationlocation){

}



@OverridepublicvoidonConnectionFailed(ConnectionResultconnectionResult){

}

As the names suggests, OnConnected is fired when the the service is connected to our LocationClientobject. Here is where we have to register our LocationListener to listen for location updates. So, we editthis method body as follows

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@OverridepublicvoidonConnected(Bundlebundle){myLocationClient.requestLocationUpdates(REQUEST,this);}

As you already know, the this in the requestLocationUpdates call is the reference to our MainActivitysince we are implementing the LocationListener Interface here. The first parameter is theLocationRequest object that sets options for the location updates such as update frequency, accuracy etc.This is defined as follows:

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privatestaticfinalLocationRequestREQUEST=LocationRequest.create().setInterval(5000)//5seconds.setFastestInterval(16)//16ms=60fps.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);

In this application, we do not do anything for onDisconnected() and onConnectionFailed() methodsand we leave them alone.

Once all these are setup, we are now ready to update our location on the map whenever we receive a newlocation update from the Location service through the onLocationChanged(Locationlocation) methodthat we registered with the LocationClient. OnLocationChanged is called back with Location parameterthat gives as our current location. To move our map to show our current location or any other location in theview. The map view is modeled as a camera looking down on a flat plane. The position of the camera andhence the rendering of the map is specified by latitude, longitude, zoom, tilt, and bearing of the location tobe shown. So, to show a given location on map, we update the camera to that location. The safest way tomove camera to our location is to use moveCamera() method in the GoogleMap class with callbacks asfollows. The callbacks prevent the situation where the map is not rendered completely and we are attemptingto update the camera.

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myMap.moveCamera(CameraUpdateFactory.newCameraPosition(newCameraPosition.Builder().target(newLatLng(lat,lng)).zoom(15.5f).bearing(0).tilt(25).build()),newGoogleMap.CancelableCallback(){@OverridepublicvoidonFinish(){//YourcodeheretodosomethingaftertheMapisrendered}

@OverridepublicvoidonCancel(){



//YourcodeheretodosomethingaftertheMaprenderingiscancelled}});

In essence, what we have done so far should result in an application that loads a map and shows our positionon it with a blue arrow. This icon will track our location on the map as we move around. However, we haveneglected some of the details, for the sake of simplicity here. For instance, we have neglected the life cycleevents of the MainActivity where is could be Paused and Resumed etc. In the event of another activitydisplayed over our MainActivity,preventing it from displaying, our MainActivity will be Paused andsent to the background and an onPause()event is generated. When the user gets back to our activity, it willbe Resumed and an onResume() event is generated. Location updates are expensive in terms of battery life.So, as a responsible citizen of the Android application habitat, our application should disable location updateswhen sent to background and not displayed and enable back again when resumed. This is done by overridingonPause() and onResume() methods of the MainActivity. Please refer to the complete application in thesource code bundle.

To use the source code and create an application for your own, please follow these steps:

1. Unzip the source in a folder2. Since Creating API key needs an application name, follow what we said in this article, starting with

creating new project in Android Studio, with your preferred application name.3. Then copy the contents of MainActivity.java from the source you unzipped and paste it in your new

MainActivity.java completely replacing the contents. Then go over to the very first line in the file andchange the line "package com.siriusmicrotech.gpsplotter with your package name that you used duringyour new project creation.

4. Copy the contents of activity_main.xml file from the source you unzipped and paste it in your newactivity_main.xml file replacing the contents entirely.

5. Copy and paste contents of build.gradle file from unzipped source on to your new buld.gradle filereplacing contents entirely.

6. Do the same for AndroidManifest.xml file. However, here, you have to change the third line from top toreplace com.siriusmicrotech.gpsplotter with your package name and under the tag, change android:name="com.siriusmicrotech.gpsplotter.MainActivity" with youractivity name.

7. Get your API key from Google Could Services8. Copy and paste your API key in the AndroidManifest.xml file to replace string that reads "Your API Key

Here!"9. That's it.

Points of InterestThings to pay attention to Get the latest version of Android Studio build. If you decided to use AndroidStudio, do not research on the internet for solutions, since almost all the text is written for Eclipse. There is asignificant change in the way things are done in Google Maps Android API V2 than it was done in V1. Most ofthe text in elsewhere in internet are written with reference to V1 and that would cripple your progress real bad.The solution is to head over to Google Developer site for API V2 and you will be much better off.

License



Raja.D.SinghFounder Sirius Microtech LLC United States

Raja.D.Singh is one of the Founders of Sirius Microtech LLC, a Los Angeles based technology companydedicated to provide Innovative Engineering services and excellent, standards compliant solutions forproblems faced by Small to Medium sized engineering organizations. Sirius specializes in New Productdevelopment for Industrial Automation, Robotics, Alternative Energy and Real Time Embedded Systems.

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This article, along with any associated source code and files, is licensed under The Code Project Open LicenseCPOL

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