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G'day everyone, welcome back.

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At the end of the last video,
we were able to add new tasks the database,

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but the RecyclerView wasn't updating to display them.

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We had to close the app and run it again to see the new tasks.

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That's not exactly the ideal user experience.

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Fortunately, all the support to make the RecyclerView
update is built into the Android framework.

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So the changes we need to make to our
ContentProvider are really simple.

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Where it gets a bit more complex is getting the ViewModel to react
to the notifications that the ContentProvider will issue.

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With the CursorLoader all this was handled for us.

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Now we have to do it ourselves.

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One thing you may be asking is, why does he keep talking about loaders when they've been deprecated.

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The answer is simple.

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If loaders are deprecated, they're going to be removed from Android at some point over the next couple of years.

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But before that happens,

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companies that have apps that used loaders

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are going to be looking for programmers that
can make them work without the loaders.

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After completing this section, you'll be one of those programmers.

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Okay there are two parts to this.
The first step is something that I've hinted at a few times.

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We need to modify our ContentProvider, so that it notifies any observers about changes to the data.

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Our ContentProvider has three functions
that can result in changes to the data;

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the insert, update and delete functions.

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The code we need to add is very similar for all three, so let's start with the insert function in the AppProvider.

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Open our AppProvider, scroll down a bit, and the change is simple.

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If something was inserted then
the record ID will be non-zero.

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Let's log that we're starting,

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and then we'll call the notifyChange function

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with the URI of the value that has changed.

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Notice that we're passing the original URI that was provided to the insert function.

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The URI that the function returns
will have the new ID appended to it

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and that refers to a specific row in the table.

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It is the URI for the entire table that we want to notify changes on.

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I used the safe call operator when getting the
ContentResolver from the context.

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We know the context won't be null,
but using the safe call operator removes warnings.

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We do something very similar for the update function.

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Scroll down a little way further, and once again
check that the count is greater than zero.

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That makes sure something happened.

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Log that we've started, and then call the
ContextResolver to notify the change,

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again, passing the URI.

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The final change is to the delete function.

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Once again, it's pretty much the same.

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That's the first part done.

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When we call a function of the ContentProvider
that results in a change to the database,

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the ContentResolver will notify any observers about the change.

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The second part is to observe these notifications.

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We do that in the TaskTimerViewModel class.

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We need to create a ContentObserver and register it.
Let's start by creating a ContentObserver.

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If you're prompted for the correct import in the handler, we want android.os.handler.

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When a change is notified, the onChange function will be called.

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We log the fact, then we call loadTasks to reload the data, and update the current cursor LiveData.

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The next step is to register the observer,
and the init code is a good place to do that.

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We tell it the URI that we want to observe changes on

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and provide our ContentObserver.

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In an app with many tables that get updated,
we can create an observer for each URI,

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or we could register the same observer for several URIs.

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Notice that the URI is passed into the
onChange function on line 22,

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so we could respond differently to different URIs.

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When you register an observer like this,
it's important to unregister it again.

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If you don't, you can end up with memory leaks.

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Remember from our discussion on ViewModels,
that they have an onCleared function.

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That function gets called when the ViewModel's no longer used and can be destroyed.

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It's a good place to clear up any resources,
and that's where we'll unregister our observer.

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Android studio will generate the stub for us.

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ctrl o, select onCleared

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remove what's already there, and add our code.

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Unregistering the observer is similar to registering it.

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We call the ContentResolver's
unregisterContentObserver function.

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Let's see that running

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We should be up to task 7

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but we'll set the sort order to 2.

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That way it should appear on the list before task 6.

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I'll click Save, and when I return to the main screen
there's our new task 7 showing in the list.

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Let's have a look in the logcat,

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and also see how to fix a quirk that it's got at the moment.

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If you find your log cat running wild and logging all sorts of things,

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even when you've got the show only selected application
filter on the right,

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don't panic.

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Use the second drop down from the left
and select your application again.

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That causes it to respect the filter.
It seems to be a quirk in Android Studio at the moment.

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Ok, type the filter, query|insert, with the regex box checked.

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That will make it easier to find what we want.

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There's our insert happening, and just below that
we can see the query being called.

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So our ViewModel has re-queried the database
to refresh its cursor.

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It then updates the database cursor MutableLiveData object,
which is being observed by the MainActivityFragment.

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When the MainActivityFragment observes that the cursor has changed,

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it swaps the adapter's cursor and the RecyclerView can immediately access the new data.

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There are two important changes we had to make,
to make all that happen.

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Firstly, we made sure that all our functions that can change the database; insert, delete and update,

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in the AppProvider,

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call the ContentResolver's notifyChange function.

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And so they notify the listeners that
there's been a change.

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Then, we set up a ContentObserver in the ViewModel class,

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and registered it to be notified of the changes.

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Okay, we'll stop the video there.

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In the next video, we'll work on the onClick listeners for the buttons,

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so that we can then edit and delete tasks.

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By the time we've done that, you should be able to tell me what we're doing wrong.

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Our code works, but we're doing something that we really shouldn't be doing.

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It's something we've seen mentioned in the documentation,

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and we've hinted at it a couple of times.

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We'll be putting it right in a future video, but until then,
see if you can work out what it is.

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See you in the next video