Android Topics

1. Android Topics UI Thread and Limited processing resources Construct an exploratory app Three Experiments to test Threads

2. What are Intents? • Most apps require us to send intents • Example: the Coffee Ordering App will require us to send off the order summary in an email. • The app must launch an email app that exists on the device. • An intent is a message that requests some type of action to be performed by another app component. This could be a camera, email, Google Maps, or even an activity in another app.

3. Limited Processing Resources • Mobile devices have a lot of resource constraints: memory and CPU (processing power). • Low-processing devices must consider background threads for heavy processing.

4. UI Thread • UI Thread is the main thread of execution. • All your code runs on the UI thread by default. • The UI Thread is important thread for interacting with your user. • Being able to design code that doesn’t blocking the UI thread is a very important concept.

5. Exploratory App • Experiment with code that runs on UI thread. • What happens when time-consuming work is done on the main thread. • How can we use a background thread for time-consuming work? TASK: Build the layout.

6. Experiment 1 • Start work Button and End work Button. • Test the app using a non intensive workload, displaying a message in the Log.i. public void workItOut(View view){ if (view.getId() == R.id.start_button)Log.i("THREAD DEMO", "Working on it"); elseLog.i("THREAD DEMO", "Not Working"); }

7. Experiment 2 • Send an unreasonable amount of output to the log window when the user clicks “Start Work”. • The logcat should fill up with the string “Working on it”. • Implement this by throw the Log.istatement in a loop and only stop when the user clicks the button labelled “Stop Work”. • What happens?

8. Experiment 2 Produces a ANRWhy?

9. Why did the ANR occur? • The loop work is completely taking over the the UI Thread. • Too much work on this thread often leads to a poor performing app or an application that doesn’t respond (ANR – Application Not Responding). • The UI Thread MUST be able to respond to the user. • Resource intensive work should never be done on the UI thread. Once it is blocked, it cannot handle anything else.

10. Android Operating System • At runtime, Android Operating System hosts app as a process. • Each app gets a dedicated process for execution.

11. Consider an Individual Process/App • There can be any number of threads in a process. • In most apps, there is a need to be smart in how you allocate work for the main thread, shown in red. • If you have a task that takes a significant amount of time, such as 5 to 3 seconds, then it will block the UI Thread and eventually seriously impact the app.

12. Background Thread • A best approach is to move time-consuming work off the main UI thread. • Create a separate thread to can handle all tasks interfering with the main UI thread. An App can have multiple threads of execution running concurrently.

13. Creating a Background Thread in Java • The class Thread implements Runnable. • Runnable is an interface specifically for executing background threads. • The Thread must define a method called run().

14. Solution to Experiment 3: public void workItOut(View view) {if (view.getId() == R.id.start_button) {if (!isDoingWork) {isDoingWork= true;new Thread(new Runnable() { @Overridepublic void run() {while (isDoingWork)Log.i("THREAD DEMO", "Working on it"); } }).start(); } } else {isDoingWork= false; }}

15. Operations which should be carried out on separate threads. • Heavy calculations • Long initialization • Networking • Database operations