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14 Photography Portfolio Themes for WordPress

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The Portable Guitarist—Transporting and Mounting an iOS Rig

The Portable Guitarist—Transporting and Mounting an iOS Rig

So far in this series, I’ve shown you the advantages of using an iOS-based live rig, as well the tech most suited to the job. 

• The Portable Guitarist—Using iOS as a Live Rig
• The Portable Guitarist—Hardware

In this tutorial, I’ll show you how to safely transporting the gear, and how to ensure you have it to hand in a live environment when you need it.

Safety First

I'll be honest: the iPad’s amazing, but it’s still more fragile—and sometimes more expensive—than a typical piece of a guitarist’s gigging equipment. A guitar or amp might survive being knocked over, but an iPad’s less likely to. 

Furthermore it’s easier to steal, and often more in demand, than a guitar. So choose a gig wisely. There'll be a difference between performing on a raised stage or playing in a rough pub where the audience keep clattering into you. 

Here are some things to think about.

Surviving the Journey

You’ve got to get the iPad, interface, and cables to and from the gig. Chucking it all into your guitar’s gig bag’s an option, and attractive if you need to travel light, but think about the level of protection offered. 

As the screen’s the most vulnerable part, consider the Smart Cover from Apple; it clips magnetically to the device, and prices typically start from around £40.

I’m a great believer in rarely relying on a single solution. My iPad’s fitted with a Belkin Snap Case. It’s a thick covering for the back, costing less than £10. It then goes into a Belkin Pleated Sleeve, a padded, double-zipped pouch for under £15. Both items have easily survived several years of daily usage.

In terms of transporting to and from gigs, I use a shoulder bag; this carries the iPad, interface, plus a wealth of cabling. I’ve opted for this as it’s hands free (like I haven’t got enough to carry at a gig), and occupies little space in the car (an important consideration).

It’s also easier to keep it with me, alleviating concerns regarding theft. Alternatively, an aluminium flight case could be bought from a retailer, such as Maplin, for as little as £25. These usually contain foam, which could be sculpted to your devices accordingly.

Mounting Options for a Device

Unless you’ve a friendly/cheap guitar tech to hand, chances are you’re going to have to operate the iPad during the gig. This means having it within reach. There are several options available to you.

Desktop

If the gig’s small, you could place the iPad in a stand atop a speaker cabinet or table. For this, there’s the iKlip Studio from IK Multimedia, available for under £30. It takes your device either in portrait or landscape, has a place for attaching one of their iRig interfaces, and folds away almost flat—save for the lip on which the device sits.

Whilst they’re very useful—I own one—I’d only recommend it for home use, or small gigs where there’s no possibility of the audience getting anywhere near it. The potential for damage is too great. Fine for an intimate, seated singer-songwriter type of gig, but little else.

Stands

There’s the age-old route of the small folding music stand. They’re designed to be extremely portable, and are REALLY cheap—often less than £10. There’s nothing, however, to stop any sideways movement of the device. 

Furthermore, their portability means that they’re flimsy—you only need the main wing nut to fail, and the iPad will be sailing backwards very quickly.

If the music stand appeals, but robustness concerns you, the opposite end of the spectrum is the lectern-style stand. These usually comprise folding feet and telescopic tubes more typically associated with speaker cabinet stands. 

A large lipped top provides plenty of support and surface area, giving you somewhere to safely put both your device and interface. Many are also perforated, so you shouldn’t worry about the device overheating. Price-wise, you can spend little or lots, but £20 will get you the type of orchestral music stands you see in schools.

Whilst sturdier, their big disadvantage is portability, or lack thereof. The feet and the tubing are collapsable, but the actual top isn’t, so what you gain in surface area costs you in terms of having to cart it around.

Cradles

As I already use a microphone stand, I prefer a cradle that attaches to it. This means that there’s little extra to bring, it’s very portable, occupies no additional floor space, plus associated cabling can run down the mic stand. 

There are many from which to choose, and they don’t have to be expensive; indeed, some are under £15. However, you get what you pay for, and I’d rather not trust the well-being of an expensive device by going for the cheapest one available.

My choice is the iPad stand from König & Meyer (also known as K&M). The cradle’s far thicker than many of its competitors, plus the fixings are reassuringly industrial. Choose from one that screws directly onto the thread of a mic stand—although you can’t now attach a mic—or one that mounts on an arm that clamps lower down the stand.

The cradle itself can orient either landscape or portrait, and can also be angled back, so exact positioning is achievable. I prefer waist height. The interface can fix to the arm. I use Velcro. Best of all, such choice and sturdiness only costs £20 to £30.

Conclusion

Using iOS live is a different proposition to home usage, so think about the following:

• Choose your gig appropriately
• How the device will be transported
• How the device will be protected
• Balance portability with robustness
• Consider the footprint a stand will occupy
• A desktop stand’s only appropriate for quiet, intimate gigs
• A folding stand’s cheap and portable, but flimsy
• Lectern stands are robust, but bulky
• A cradle and clamp is a compact, safe, portable solution

In the next tutorial, I’ll cover output connections and cabling, plus best choices of amplification.

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Building RESTful APIs With Flask: ORM Independent

Building RESTful APIs With Flask: ORM Independent

In the first part of this three-part tutorial series, we saw how to write RESTful APIs all by ourselves using Flask as the web framework. In the second part, we created a RESTful API using Flask-Restless which depends on SQLAlchemy as the ORM. In this part, we will use another Flask extension, Flask-Restful, which abstracts your ORM and does not make any assumptions about it. 

I will take the same sample application as in the last part of this series to maintain context and continuity. Although this example application is based on SQLAlchemy itself, this extension can be used along with any ORM in a similar fashion, as shown in this tutorial.

Installing Dependencies

While continuing with the application from the first part, we need to install only one dependency:

$ pip install Flask-Restful

The Application

Before we start, you might want to remove the code that we wrote for the second part of this tutorial series for more clarity.

As always, we will start with changes to our application's configuration, which will look something like the following lines of code: 

flask_app/my_app/__init__.py

from flask.ext.restful import Api

api = Api(app)

Just adding the above couple of lines to the existing code should suffice.

flask_app/my_app/catalog/views.py

import json
from flask import Blueprint, abort
from flask.ext.restful import Resource
from flask.ext.restful import reqparse
from my_app.catalog.models import Product
from my_app import api, db


catalog = Blueprint('catalog', __name__)

parser = reqparse.RequestParser()
parser.add_argument('name', type=str)
parser.add_argument('price', type=float)


@catalog.route('/')
@catalog.route('/home')
def home():
    return "Welcome to the Catalog Home."


class ProductApi(Resource):

    def get(self, id=None, page=1):
        if not id:
            products = Product.query.paginate(page, 10).items
        else:
            products = [Product.query.get(id)]
        if not products:
            abort(404)
        res = {}
        for product in products:
            res[product.id] = {
                'name': product.name,
                'price': product.price,
            }
        return json.dumps(res)

    def post(self):
        args = parser.parse_args()
        name = args['name']
        price = args['price']
        product = Product(name, price)
        db.session.add(product)
        db.session.commit()
        res = {}
        res[product.id] = {
            'name': product.name,
            'price': product.price,
        }
        return json.dumps(res)

api.add_resource(
   ProductApi,
   '/api/product',
   '/api/product/<int:id>',
   '/api/product/<int:id>/<int:page>'
)

Most of the code above is self-explanatory. I will highlight a few points, though. The code above seems very similar to the one that we wrote in the first part of this series, but here the extension used does a bunch of behind-the-scenes optimizations and provides a lot more features that can be leveraged. 

Here the methods declared under any class that subclasses Resource are automatically considered for routing. Also, any parameters that we expect to receive along with incoming HTTP calls need to be parsed using reqparse.

Testing the Application

This application can be tested in exactly the same way as we did in the second part of this tutorial series. I have kept the routing URL the same for the same purpose.

Conclusion

In this last part of this three-part tutorial series on developing RESTful APIs with Flask, we saw how to write ORM-independent RESTful APIs. This wraps up the basics of writing RESTful APIs with Flask in various ways. 

There is more that can be learned about each of the methods covered, and you can explore this on your own, using the basics you've learned in this series.

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Let's Go: Testing Golang Programs

Let's Go: Testing Golang Programs

In this tutorial I will teach you all the basics of idiomatic testing in Go using the best practices developed by the language designers and the community. The main weapon will be the standard testing package. The target will be a sample program that solves a simple problem from Project Euler.

Square Sum Difference

The sum square difference problem is pretty simple: "Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum." 

This particular problem can be solved rather concisely especially if you know your Gauss. For example, the sum of the first N natural numbers is (1 + N) * N / 2, and the sum of squares of the first N integers is: (1 + N) * (N * 2 + 1) * N / 6. So the whole problem can be solved by the following formula and assigning 100 to N:

(1 + N) * (N * 2 + 1) * N / 6 - ((1 + N) * N / 2) * ((1 + N) * N / 2)

Well, that's very specific, and there isn't much to test. Instead, I created some functions that are a little more general than what's needed for this problem, but can serve for other programs in the future (project Euler has 559 problems right now).

The code is available on GitHub.

Here are the signatures of the four functions:

// The MakeIntList() function returns an array of consecutive integers

// starting from 1 all the way to the `number` (including the number)

func MakeIntList(number int) []int



// The squareList() function takes a slice of integers and returns an

// array of the quares of these integers

func SquareList(numbers []int) []int



// The sumList() function takes a slice of integers and returns their sum

func SumList(numbers []int) int



// Solve Project Euler #6 - Sum square difference

func Process(number int) int

Now, with our target program in place (please forgive me, TDD zealots), let's see how to write tests for this program.

The Testing Package

The testing package goes hand in hand with the go test command. Your package tests should go in files with the "_test.go" suffix. You can split your tests across several files that follow this convention. For example: "whatever1_test.go" and "whatever2_test.go". You should put your test functions in these test files.

Every test function is a publicly exported function whose name starts with "Test", accepts a pointer to a testing.T object, and returns nothing. It looks like:

func TestWhatever(t *testing.T) {
    // Your test code goes here
} 

The T object provides various methods you can use to indicate failure or record errors.

Remember: only test functions defined in test files will be executed by the go test command.

Writing Tests

Every test follows the same flow: set up the test environment (optional), feed the code under test input, capture the result, and compare it to the expected output. Note that inputs and results don't have to be arguments to a function. 

If the code under test is fetching data from a database then the input will be making sure the database contains appropriate test data (which may involve mocking at various levels). But, for our application, the common scenario of passing input arguments to a function and comparing the result to the function output is sufficient.

Let's start with the SumList() function. This function takes a slice of integers and returns their sum. Here is a test function that verifies SumList() behaves as it should.

It tests two test cases, and if an expected output doesn't match the result, it calls the Error() method of the testing.T object. 

func TestSumList_NotIdiomatic(t *testing.T) {
    // Test []{} -> 0
    result := SumList([]int{})
    if result != 0 {
            t.Error(
                "For input: ", []int{},
                "expected:", 0,
                "got:", result)
    }

    // Test []{4, 8, 9} -> 21
    result = SumList([]int{4, 8, 9})
    if result != 21 {
            t.Error(
                "For input: ", []int{},
                "expected:", 0,
                "got:", result)
    }
}

This is all straightforward, but it looks a little verbose. Idiomatic Go testing uses table-driven tests where you define a struct for pairs of inputs and expected outputs and then have a list of these pairs that you feed in a loop to the same logic. Here is how it is done for testing the SumList() function.

type List2IntTestPair struct {
    input  []int
    output int
}


func TestSumList(t *testing.T) {
    var tests = []List2IntTestPair{
        {[]int{}, 0},
        {[]int{1}, 1},
        {[]int{1, 2}, 3},
        {[]int{12, 13, 25, 7}, 57},
    }

    for _, pair := range tests {
        result := SumList(pair.input)
        if result != pair.output {
            t.Error(
                "For input: ", pair.input,
                "expected:", pair.output,
                "got:", result)
        }
    }
}

This is much better. It is easy to add more test cases. It's easy to have the full spectrum of test cases in one place, and if you decide to change the test logic you don't need to change multiple instances.

Here is another example for testing the SquareList() function. In this case, both the input and the output are slices of integers, so the test pair struct is different, but the flow is identical. One interesting thing here is that Go doesn't provide a built-in way to compare slices, so I use reflect.DeepEqual() to compare the output slice to the expected slice.

type List2ListTestPair struct {
    input  []int
    output []int
}

func TestSquareList(t *testing.T) {
    var tests = []List2ListTestPair{
        {[]int{}, []int{}},
        {[]int{1}, []int{1}},
        {[]int{2}, []int{4}},
        {[]int{3, 5, 7}, []int{9, 25, 49}},
    }

    for _, pair := range tests {
        result := SquareList(pair.input)
        if !reflect.DeepEqual(result, pair.output) {
            t.Error(
                "For input: ", pair.input,
                "expected:", pair.output,
                "got:", result)
        }
    }
}

Running Tests

Running tests is as simple as typing go test in your package directory. Go will find all the files with the "_test.go" suffix and all the functions with the "Test" prefix and run them as tests. Here is what it looks like when everything is OK:

(G)/project-euler/6/go > go test

PASS

ok      _/Users/gigi/Documents/dev/github/project-euler/6/go    0.006s

Not very dramatic. Let me break a test on purpose. I'll change the test case for SumList() such that the expected output for summing 1 and 2 will be 7.

func TestSumList(t *testing.T) {
    var tests = []List2IntTestPair{
        {[]int{}, 0},
        {[]int{1}, 1},
        {[]int{1, 2}, 7},
        {[]int{12, 13, 25, 7}, 57},
    }

    for _, pair := range tests {
        result := SumList(pair.input)
        if result != pair.output {
            t.Error(
                "For input: ", pair.input,
                "expected:", pair.output,
                "got:", result)
        }
    }
}

Now, when you type go test, you get:

(G)/project-euler/6/go > go test

--- FAIL: TestSumList (0.00s)

006_sum_square_difference_test.go:80: For input:  [1 2] expected: 7 got: 3

FAIL

exit status 1

FAIL    _/Users/gigi/Documents/dev/github/project-euler/6/go    0.006s

That states pretty well what happened and should give you all the information you need to fix the problem. In this case, the problem is that the test itself is wrong and the expected value should be 3. That's an important lesson. Don't automatically assume that if a test fails the code under test is broken. Consider the entire system, which includes the code under test, the test itself, and the test environment.

Test Coverage

To ensure your code works, it's not enough to have passing tests. Another important aspect is test coverage. Do your tests cover every statement in the code? Sometimes even that is not enough. For example, if you have a loop in your code that runs until a condition is met, you may test it successfully with a condition that works, but fail to notice that in some cases the condition may always be false, resulting in an infinite loop. 

Unit Tests

Unit tests are like brushing your teeth and flossing. You shouldn't neglect them. They are the first barrier against problems and will let you have confidence in refactoring. They are also a boon when trying to reproduce issues and being able to write a failing test that demonstrates the issue that passes after you fix the issue.

Integration Tests

Integration tests are necessary as well. Think of them as visiting the dentist. You may be OK without them for a while, but if you neglect them for too long it won't be pretty. 

Most non-trivial programs are made of multiple inter-related modules or components. Problems can often occur when wiring those components together. Integration tests give you confidence that your entire system is operating as intended. There are many other types of tests like acceptance tests, performance tests, stress/load tests and full-fledged whole system tests, but unit tests and integration tests are two of the foundational ways to test software.

Conclusion

Go has built-in support for testing, a well-defined way to write tests, and recommended guidelines in the form of table-driven tests. 

The need to write special structs for every combination of inputs and outputs is a little annoying, but that's the price you pay for Go's simple by design approach.

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Concurrency on Android with Service

Concurrency on Android with Service

In this tutorial we’ll explore the Service component and its superclass, the IntentService. You'll learn when and how to use this component to create great concurrency solutions for long-running background operations. We’ll also take quick look at IPC (Inter Process Communication), to learn how to communicate with services running on different processes.

To follow this tutorial you'll need some understanding of concurrency on Android. If you don’t know much about it, you might want to read some of our other articles about the topic first.

• 
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  Android From Scratch: Background Operations
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• 
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1. The Service Component

The Service component is a very important part of Android's concurrency framework. It fulfills the need to perform a long-running operation within an application, or it supplies some functionality for other applications. In this tutorial we’ll concentrate exclusively on Service’s long-running task capability, and how to use this power to improve concurrency.

What is a Service?

A Service is a simple component that's instantiated by the system to do some long-running work that doesn't necessarily depend on user interaction. It can be independent from the activity life cycle and can also run on a complete different process.

Before diving into a discussion of what a Service represents, it's important to stress that even though services are commonly used for long-running background operations and to execute tasks on different processes, a Service doesn't represent a Thread or a process. It will only run in a background thread or on a different process if it's explicitly asked to do so.

A Service has two main features:

• A facility for the application to tell the system about something it wants to be doing in the background.
• A facility for an application to expose some of its functionality to other applications.
  

Services and Threads

There is a lot of confusion about services and threads. When a Service is declared, it doesn't contain a Thread. As a matter of fact, by default it runs directly on the main thread and any work done on it may potentially freeze an application. (Unless it's a IntentService, a Service subclass that already comes with a worker thread configured.)

So, how do services offer a concurrency solution? Well, a Service doesn't contain a thread by default, but it can be easily configured to work with its own thread or with a pool of threads. We'll see more about that below.

Disregarding the lack of a built-in thread, a Service is an excellent solution for concurrency problems in certain situations. The main reasons to choose a Service over other concurrency solutions like AsyncTask or the HaMeR framework are:

• A Service can be independent of activity life cycles.
• A Service is appropriate for running long operations.
• Services don't depend on user interaction.
• When running on different processes, Android can try to keep services alive even when the system is short on resources.
• A Service can be restarted to resume its work.

Service Types

There are two types of Service, started and bound.

A started service is launched via Context.startService(). Generally it performs only one operation and it will run indefinitely until the operation ends, then it shuts itself down. Typically, it doesn't return any result to the user interface.

The bound service is launched via Context.bindService(), and it allows a two-way communication between client and Service. It can also connect with multiple clients. It destroys itself when there isn't any client connected to it.

To choose between those two types, the  Service must implement some callbacks: onStartCommand() to run as a started service, and onBind() to run as a bound service. A Service may choose to implement only one of those types, but it can also adopt both at the same time without any problems. 

2. Service Implementation

To use a service, extend the Service class and override its callback methods, according to the type of Service . As mentioned before, for started services the onStartCommand() method must be implemented and for bound services, the onBind() method. Actually, the onBind() method must be declared for either service type, but it can return null for started services.

public class CustomService extends Service {
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // Execute your operations
        // Service wont be terminated automatically
        return Service.START_NOT_STICKY;
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        // Creates a connection with a client
        // using a interface implemented on IBinder
        return null;
    }
}

• onStartCommand(): launched by Context.startService(). This is usually called from an activity. Once called, the service may run indefinitely and it's up to you to stop it, either calling stopSelf() or stopService().
• onBind(): called when a component wants to connect to the service. Called on the system by Context.bindService(). It returns an IBinder that provides an interface to communicate with the client.

The service's life cycle is also important to take into consideration. The onCreate()  and onDestroy() methods should be implemented to initialize and shut down any resources or operations of the service.

Declaring a Service on Manifest

The Service component must be declared on the manifest with the <service> element. In this declaration it's also possible, but not obligatory, to set a different process for the Service to run in.

<manifest ... >
  ...
  <application ... >
      <service 
        android:name=".ExampleService"
        android:process=":my_process"/>
      ...
  </application>
</manifest>

2.2. Working with Started Services

To initiate a started service you must call Context.startService() method. The Intent must be created with the Context and the Service class. Any relevant information or data should also be passed in this Intent.

Intent serviceIntent = new Intent(this, CustomService.class);
// Pass data to be processed on the Service
Bundle data = new Bundle();
data.putInt("OperationType", 99);
data.putString("DownloadURL", "http://ift.tt/2ebEbhI");
serviceIntent.putExtras(data);
// Starting the Service
startService(serviceIntent);

In your Service class, the method that you should be concerned about is the onStartCommand(). It's on this method that you should call any operation that you want to execute on the started service. You'll process the Intent to capture information sent by the client. The startId represents an unique ID, automatically created for this specific request and the flags can also contain extra information about it.

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        Bundle data = intent.getExtras();
        if (data != null) {
            int operation = data.getInt(KEY_OPERATION);
            // Check what operation to perform and send a msg
            if ( operation == OP_DOWNLOAD){
                // make a download
            }
        }

        return START_STICKY;
    }

The onStartCommand() returns a constant int that controls the behavior:

• Service.START_STICKY: Service is restarted if it gets terminated.
  
• Service.START_NOT_STICKY: Service is not restarted.
  
• Service.START_REDELIVER_INTENT: The service is restarted after a crash and the intents then processing will be redelivered.
  

As mentioned before, a started service needs to be stopped, otherwise it will run indefinitely. This can be done either by the Service calling stopSelf() on itself or by a client calling stopService() on it.

void someOperation() {
        // do some long-running operation
        // and stop the service when it is done
        stopSelf();
    }

Binding to Services

Components can create connections with services, establishing a two-way communication with them. The client must call Context.bindService(), passing an Intent, a ServiceConnection interface and a flag as parameters. A Service can be bound to multiple clients and it will be destroyed once it has no clients connected to it.

void bindWithService() {
        Intent intent = new Intent(this, PlayerService.class);
        // bind with Service
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

It's possible to send Message objects to services. To do it you'll need to create a Messenger on the client side in a ServiceConnection.onServiceConnected interface implementation and use it to send Message objects to the Service.

private ServiceConnection mConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName className,
                                       IBinder service) {
            // use the IBinder received to create a Messenger
            mServiceMessenger = new Messenger(service);
            mBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0) {
            mBound = false;
            mServiceMessenger = null;
        }
    };

It's also possible to pass a response Messenger to the Service for the client to receive messages. Watch out though, because the client may not no longer be around to receive the service's message. You could also use BroadcastReceiver or any other broadcast solution.

    private Handler mResponseHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // handle response from Service
        }
    };
    Message msgReply = Message.obtain();
    msgReply.replyTo = new Messenger(mResponseHandler);
    try {
        mServiceMessenger.send(msgReply);
    } catch (RemoteException e) {
        e.printStackTrace();
    }

It's important to unbind from the Service when the client is being destroyed.

@Override
    protected void onDestroy() {
        super.onDestroy();
        // disconnect from service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }

On the Service side, you must implement the Service.onBind() method, providing an IBinder provided from a Messenger. This will relay a response Handler to handle the Message objects received from client.

    IncomingHandler(PlayerService playerService) {
            mPlayerService = new WeakReference<>(playerService);
        }

        @Override
        public void handleMessage(Message msg) {
            // handle messages
        }
    }
    
    public IBinder onBind(Intent intent) {
        // pass a Binder using the Messenger created
        return mMessenger.getBinder();
    }
    
    final Messenger mMessenger = new Messenger(new IncomingHandler(this));

3 Concurrency Using Services

Finally, it's time to talk about how to solve concurrency problems using services. As mentioned before, a standard Service doesn't contain any extra threads and it will run on the main Thread by default. To overcome this problem you must add an worker Thread, a pool of threads or execute the Service on a different process. You could also use a subclass of Service called IntentService that already contains a Thread.

Making a Service Run on a Worker Thread

To make the Service execute on a background Thread you could just create an extra Thread and run the job there. However Android offers us a better solution. One way to take the best advantage of the system is to implement the HaMeR framework inside the Service, for example by looping a Thread with a message queue that can process messages indefinitely.

It's important to understand that this implementation will process tasks sequentially. If you need to receive and process multiple tasks at the same time, you should use a pool of threads. Using thread pools is out of the scope of this tutorial and we won't talk about it today. 

To use HaMeR you must provide the Service with a Looper, a Handler and a HandlerThread.

    private Looper mServiceLooper;
    private ServiceHandler mServiceHandler;
    // Handler to receive messages from client
    private final class ServiceHandler extends Handler {
        ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            // handle messages

            // stopping Service using startId
            stopSelf( msg.arg1 );
        }
    }
    
    @Override
    public void onCreate() {
        HandlerThread thread = new HandlerThread("ServiceThread",
                Process.THREAD_PRIORITY_BACKGROUND);
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);

    } 

If the HaMeR framework is unfamiliar to you, read our tutorials on HaMer for Android concurrency.

• 
  Android SDK
  Understanding Concurrency on Android Using HaMeR
  Tin Megali
• 
  Android SDK
  Practical Concurrency on Android With HaMeR
  Tin Megali

The IntentService

If there is no need for the Service to be kept alive for a long time, you could use IntentService, a Service subclass that's ready to run tasks on background threads. Internally, IntentService is a Service with a very similar implementation to the one proposed above. 

To use this class, all you have to do is extend it and implement the onHandleIntent(), a hook method that will be called every time a client calls startService() on this Service. It's important to keep in mind that the IntentService will stop as soon as its job is completed.

public class MyIntentService extends IntentService {
    
    public MyIntentService() {
        super("MyIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        // handle Intents send by startService
    }
}

IPC (Inter Process Communication)

A Service can run on a completely different Process, independently from all tasks that are happening on the main process. A process has its own memory allocation, thread group, and processing priorities. This approach can be really useful when you need to work independently from the main process.

Communication between different processes is called IPC (Inter Process Communication). In a Service there are two main ways to do IPC: using a Messenger or implementing an AIDL interface. 

We've learned how to send and receive messages between services. All that you have to do is use create a Messenger using the IBinder instance received during the connection process and use it to send a reply Messenger back to the Service.

    private Handler mResponseHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // handle response from Service
        }
    };

    private ServiceConnection mConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName className,
                                       IBinder service) {
            // use the IBinder received to create a Messenger
            mServiceMessenger = new Messenger(service);

            Message msgReply = Message.obtain();
            msgReply.replyTo = new Messenger(mResponseHandler);
            try {
                mServiceMessenger.send(msgReply);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

The AIDL interface is a very powerful solution that allows direct calls on Service methods running on different processes and it's appropriate to use when your Service is really complex. However, AIDL is complicated to implement and it's rarely used, so its use won't be discussed in this tutorial.

4. Conclusion

Services can be simple or complex. It depends on the needs of your application. I tried to cover as much ground as possible on this tutorial, however I've focused just on using services for concurrency purposes and there are more possibilities for this component. I you want to study more, take a look at the documentation and Android guides. 

See you soon!

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