Herein, please find a modified version of the code from Demo 5.
There are a few things to take note of, which may be helpful for your projects.
The most important thing to do is to compare TimeService and OrientationService, and their
respective tests. TimeService has been refactored to use
MediatorLiveData,
a very helpful implementation of LiveData that allows adding and removing sources. You can think
of it as a way to merge multiple other LiveData, or in our case to switch data sources behind
the scenes without the observers needing to know, as shown in TimeService.
OrientationService has NOT been refactored this way. As a result, you can see in its test
as an example, we need a call to activity.reobserveOrientation() to tell the activity "hey you're
looking at an old data source, please ask the OrientationService for a new observable".
This is definitely not SRP! Plus, imagine if every activity that used orientation needed a method
like this! It would be a huge mess! By using MediatorLiveData behind the scenes (it is still
returned as an interface LiveData), our activities never have to re-observe.
Note: this use of MediatorLiveData is kind of like the Adapter pattern for LiveData!
All of the tests included here work and should provide a good starting place for your own testing
if you're struggling to do so with LiveData involved. Note the added rule:
@Rule
public InstantTaskExecutorRule instantTaskExecutorRule = new InstantTaskExecutorRule();
(It comes from the Gradle dependency 'androidx.arch.core:core-testing:2.1.0'.)
This rule is needed for LiveData to work properly in tests. It tells AndroidX Test that we want
to run everything on the UI thread immediately, waiting before proceeding. You can think of it as
making runOnUiThread always run immediately.
We've included an example in TaskExecutorRuleDemoTest. You can see that the test fails without
the rule, and passes with it. This is because the LiveData is not updated before the test continues.
This test also shows the use of CountdownLatch, which is a helpful little tool for testing things
which might help in the background. You can see that we use it to wait for something to happen
inside an observe lambda, and then check the value. But beware, you should never use this
without a timeout, or you could end up waiting forever!
This version of the app shows all three sensor values centered (regardless of rotation). You may find this trick of using a centered container useful somewhere in your project, even if the contents are different...
This version of the app formats all of the sensor data nicely. You won't need any of this in your project, but it serves to show some ways you can work with this data. In particular, how you can work with orientation with some standard library methods.
This version of the app also shows how to request location permissions "properly". The code I've included is a bit different than what you might find in other places online, but it's more concise.
It lightly uses the Java Streams API to make the code more readable.