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G'day everyone, welcome back.

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In the last video we got our cursor adapter working.

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Well we think it's working. We know it hasn't broken anything

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and that it works fine when there is no data,

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but we can't test it further until we've created the view model class that's going to provide it with data.

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So let's get started.

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Right click on the project and choose
New Kotlin File/Class.

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I'll call it TaskTimerViewModel

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and select class from the drop-down.

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We saw how view models worked in the previous section.

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This one's going to be a slight variation.

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Instead of extending the ViewModel class
we'll extend an Android view model.

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Both classes work the same way.
AndroidViewModel is a subclass of ViewModel,

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but it also has an application property.

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That's going to be useful if we want to access the database,

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because we'll need an application to get a ContentResolver.

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So let's complete our TaskTimerViewModel declaration.

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Additionally, of course, let's put a tag
in to help with our logging.

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It's worth control clicking on the AndroidViewModel to check out the source code.

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That's command click on a Mac.

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Once again, this is Java code.

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So it's slightly more verbose than Kotlin
but it's easy enough to understand.

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AndroidViewModel is a subclass of ViewModel.

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The Java keyword, extends, is used to specify the superclass.

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As we said, it has an application property.

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The application property is set in the constructor,
which is a separate method in Java.

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You can write constructors that way in Kotlin, but it's more convenient to just use the primary constructor,

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and list the properties when defining the class.

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Being Java, it also has a getter for the
application, the getApplication function.

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This complicates our Kotlin code slightly

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because it allows the application argument to also be
a subclass of application.

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That's what the T extends Application means.

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It can return any type as long as that type is an Application,
or a subclass of it.

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You'll see the slight complication that this causes us, shortly.

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Ok, back to our ViewModel.

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We want it to make a cursor available via a LiveData object.

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We've seen that before. When the cursor changes,
observers will be notified of that change.

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In this case, the observer will be MainActivityFragment.

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When it gets notified of a change,
it'll swap the cursor in the RecyclerviewAdapter.

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We'll make our database cursor a private variable of type MutableLiveData.

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We'll define our cursor as a LiveData cursor

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and we'll return the database cursor in the get method.

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Our ViewModel will load the data from the database then update the database cursor LiveData object.

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We'll add that code in a separate function.

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We'll define our load tasks method.

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Our projection array will define the data table's columns.

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We'll put a comment in to remind us of
what we're doing,

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and we'll define our sort order.

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Then we'll define our cursor using to projection array and the sort order.

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Then we'll set the database cursor value.

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That's the standard code for fetching data from the ContentProvider.

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What might look a bit strange is the way we have to get the ContentResolver on line 25.

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As we're using Kotlin you may expect that we could refer to the application property directly,

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rather than calling the Java getter method.

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That's the slight complication I mentioned before.

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Because we have to specify the exact type of application inside the diamond operator,

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we must use the getter.

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It's a minor inconvenience, but does make the AndroidViewModel class more flexible,

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and it does it in a type-safe way.

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If you want to store the application parameter that was passed via the constructor,

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then you could create a property to store it.

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That would work, but I wanted to show you this strange syntax.

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I've also jumped the gun a bit here.

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On line 30, I've called the postValue
function to set up our database cursor's value.

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This is instead of assigning it
directly to its value property.

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You may remember, back in the previous section,

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that postValue was used when you're updating the value on a different thread

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to the one that the MutableLiveData object was created on.

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I won't say any more about that just yet

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because I'll be giving away the answer to a mini-challenge if I do.

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Ignore the warning about closing the cursor, if you get one on line 30.

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The warning's correct, it is our responsibility to close the
cursor.

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We can't do that now though. If we do, it will be invalid when the adapter tries to get the data from it.

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I mentioned that briefly when we wrote
the swap cursor function in our adapter.

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This is what I was referring to.

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The adapter doesn't own the cursor, so it shouldn't close it.

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We'll see how to deal with this when we've finished writing all the code.

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All right, we're just about done.

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All that remains is to call that loadTasks function.

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We can do that in an init block, which will be executed when the ViewModel instance gets created.

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I like to put init code at the start of the class, after the property and the variable declarations.

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We'll make sure that we log the start

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and then call our load tasks function.

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In the next video we'll subscribe to the
ViewModel and see it working.

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See you in the next one