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Welcome back.

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In this video, we've got some slides to explain how different instances of the same ViewModel work.

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Before making the change, we can confirm that behaviour.

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I'll run the app again.

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and filter the logcat

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on tasktimerviewmodel

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to make it easier to find things, use control f and search tasktimerviewmodel

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That highlights the entries to distinguish
them from the app provider entries.

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Tap the plus button to add a new task task

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Task 9

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9th task.

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Save the task and we can see a
new TaskTimerViewModel instance

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created in the logcat.

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We can see the
entries TaskTimerViewModel created

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appearing twice

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and each one is accompanied by AppProviderQuery called with

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and the URI.

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We've already seen the
change we need to make in AddEditFragment.

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We just need to change this to activity

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We've had to use the bangbang operator
there, to provide a non nullable activity

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As we know from the fragment life cycle
the activity can be null at times.

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As a result, it is essential that we don't
attempt to use the view model any

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earlier than onActivityCreated.

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A lazy
delegate will initialize view model the

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first time it is referred to, and the
activity is non null by the time

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onActivityCreated runs.
I'll run the app again

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and keep an eye on logcat.

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I've still got the filter, to make it easier
to see just the bits that we're interested in.

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When MainActivityFragment starts,

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we get a TaskTimerViewModel instance created,

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and the database
is queried

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I'll edit task 10

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and change the word first back to the digit 1st

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when I tap save, we no longer get a new
ViewModel instance,

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and the database is only requeried after the update.

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Okay,
that's the end of this video.

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We've gone into a lot more detail about ViewModels,

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but I think it's important to understand

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the things we've covered here, if you're
going to use them without getting

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strange bugs.

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The scope that you use for
the view model is important,

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especially when using them for multiple fragments.

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In this example, and the slides,

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I've explained what's going on and why you may want to use the Activity as the

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scope, when you have more than one
Fragment at the same time.

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Our app can now

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add, edit and delete the task records.

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I'm going to stop this section here but that's not the end of our app.

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In the next section we'll use it to have a look

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at dialogues. See you in the next section