Programming is the most fun a person can have on their own. This is a fact well-known to programmers, though it seems the rest of the world is yet to catch on. You already know this or you wouldn't be reading this book, but it constantly amazes me that more people aren't falling over themselves to learn to code.
Meanwhile, mobile devices have made computers fun even for non-coders. We carry in our pockets small machines with incredible processing power and a giddying array of sensors and interfaces.
Android takes these fun machines and makes them accessible to programmers through a fabulously well-crafted platform and tool chain, in a programming language that has stood the test of time yet continues to develop and evolve.
What could possibly be better than programming fun machines to do cool things, in a powerful language, on a well-crafted platform, with a world-class tool chain? For me, the answer is doing so with a good enough understanding of those things to make the difference between a good app and a great one.
There are many things that must come together to make a great app. You need a great idea—I can't help you there. You need a pretty user interface—sorry, wrong book. You need a great user experience—aha! Now we're getting somewhere. Among the many things that contribute to a great user experience, responsiveness is right up there near the top of the list.
It's easiest to define responsiveness with examples of its lack: pauses and glitches while scrolling content, user interfaces that freeze while loading data from storage, applications that don't give progress updates to let us know what's happening, failing to complete work that we initiated, staring at a spinner while data is fetched from the network, and the list goes on.
This book is about making the difference between a good app and a great one; smoothing out the glitches, keeping the UI responsive, telling the user how things are going, making sure we finish what we started, using those powerful multicore processors, and doing it all without wasting the battery. Let's have some fun!
Chapter 1, Building Responsive Android Applications, gives an overview of the Android process and thread model, and describes some of the challenges and benefits of concurrency in general, before discussing issues specific to Android.
Chapter 2, Staying Responsive with AsyncTask, covers the poster child of concurrent programming in Android. We learn how AsyncTask works, how to use it correctly, and how to avoid the common pitfalls that catch out even experienced developers.
Chapter 3, Distributing Work with Handler and HandlerThread, details the fundamental and related topics of Handler, HandlerThread, and Looper, and illustrates how they can be used to schedule tasks on the main thread, and to coordinate and communicate work between cooperating background threads.
Chapter 4, Asynchronous I/O with Loader, introduces the Loader framework and tackles the important task of loading data asynchronously to keep the user interface responsive and glitch free.
Chapter 5, Queuing Work with IntentService, gives us the means to perform background operations beyond the scope of a single Activity lifecycle and to ensure that our work is completed even if the user leaves the application.
Chapter 6, Long-running Tasks with Service, extends the capabilities we discovered with IntentService and gives us control over the level of concurrency applied to our long-running background tasks.
Chapter 7, Scheduling Work with AlarmManager, completes our toolkit by enabling us to arrange for work to be done far into the future and on repeating schedules. It also enables us to build apps that alert users to new content and start instantly with fresh data.
To follow along and experiment with the examples, you will need a development computer with a Java 6 (or 7) SE Development Kit and the Android Software Development Kit Version 7 or above (you will need at least Version 19 to try all of the examples).
You will also need an Integrated Development Environment such as Android Studio or Eclipse. The examples have been developed using Google's new Android Studio IDE and use its integrated build system, Gradle.
While you can run the examples using the emulator provided by the Android SDK, it is a poor substitute for the real thing. A physical Android device is a much faster and more pleasurable way to develop and test Android applications!
Many of the examples will work on a device running any version of Android since 2.1, Éclair. Some examples demonstrate newer APIs and as a result, require a more recent Android version—up to Android 4.4, KitKat.
You can also download a prebuilt application containing all of the examples from Google Play; search for "Asynchronous Android".
This book is for developers who have mastered the basics of Android and are ready to take the next big step to improve the quality of your apps—not just behind the scenes engineering quality, but real perceivable improvements that make a difference to end users.
A reasonable understanding of core Android development is assumed. If you have built Android apps before and are comfortable with the Activity class and its lifecycle, XML layout files, and the Android manifest, you should have no problem understanding the topics in this book.
Familiarity with Java's concurrency primitives and higher-level constructs will aid and deepen understanding, but is not a prerequisite.
Android developers with no prior experience of concurrency and asynchronous programming will learn when, why, and how to apply Android's concurrency constructs to build responsive apps.
Java experts new to Android will be equipped to properly apply their existing knowledge in the Android environment and will discover elegant solutions to familiar problems in Android's high-level concurrency constructs.
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Code words in text are shown as follows: "We can include other contexts through the use of the include directive."
A block of code is set as follows:
protected void onPause() {
super.onPause();
if (task != null)
task.cancel(false);
}When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
protected void onPause() {
super.onPause();
if (task != null)
task.cancel(false);
}Any command-line input or output is written as follows:
> telnet 192.168.0.4 4444
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "clicking on the Next button moves you to the next screen."
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