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(vibrant music)

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(typing)

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Alright so we've got the app navigation working.

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Let's have a look at what we're gonna do

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when the back button's tapped.

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Reacting to the back button's really easy.

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Activities have an onBackPressed function that gets called.

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What we have to do to start with is decide how

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our app's going to respond to it.

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So let's get back to the app

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and start by seeing what happens at the moment,

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when we just rely on the default behaviour.

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So we're gonna bring up the emulator again.

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And you can see the emulator's in landscape.

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So we're gonna start there.

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So we'll just start the app again.

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It's been backed up.

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So if I tap the back button now, from the main screen,

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you can see it's just closed the app,

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which is exactly what the user would expect to happen.

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And the same will happen in portrait.

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And that's fine.

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So we'll run the app again now.

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This time I'm gonna click on the plus icon.

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Now we've got a different situation.

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What will the user expect back to do here?

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If they'd added some data,

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the very least we should do is ask

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for confirmation that they wanna quit editing.

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And we'll be looking at dialogues later

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and we'll see how to do that.

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If they choose to quit, should we exit the app

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or just remove the fragment?

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I personally probably want the app to exit if I was

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in this position as a user, so that's what we'll do.

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The situation's different in portrait though.

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We still got the fragment showing.

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So I rotate the device back into portrait now.

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So this is a bit different.

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As a user, I'd expect the back button

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to do the same as up from here.

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In other words, take me back to the main screen.

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That seems more expected, so that's what we'll do.

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Notice, if I press back at the moment,

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it just exits the app.

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Right, so let's get back to main activity.

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And what we need to do is add the onBackPressed function

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to main activity.

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And I'll do that towards the end of the file.

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Just before these life cycle functions,

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so I'll just do it down here.

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So let's get to override a method.

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And the method we wanna override was onBackPressed.

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So I've grabbed that one.

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We entered the default code for it.

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Alright, and it's that code

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to the super dock onBackPressed function,

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that's causing that default behaviour.

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So basically calls another function,

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the activity's finished function to close down the activity.

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We're gonna check to see if the added at fragment exists

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and changed the behaviour if it does.

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So let's start with some code.

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So I'll start by val fragment

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equals supportFragmentManager

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period findFragmentById parenthesis R dot ID dot

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task_details_container, which is our edited fragment.

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And then we'll do a test.

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If fragment is equal to null

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or bring nTwoPane, nTwoPane mode, then and only then

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will we call the super to onBackPressed.

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Otherwise, we put an else here.

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What we'll do instead is we'll removeEditPane

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and pass our fragment to that.

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So if we're not showing the fragment or

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if we're in twoPane mode then we're calling the super dock

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onBackPressed function to exit normally.

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Otherwise, we're just removing the fragment

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using our removeEditPane function.

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So as I said we'll be adding a dialogue later

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to get confirmation that the user's happy to lose any

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changes there that you may have made when editing.

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For now though, see how this works.

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We'll run the app again.

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And so my emulator's in portrait,

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so I'll start there.

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So I'm gonna click on the plus icon to display the fragment,

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then we'll click on the back button.

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So that now looks like what users will expect.

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The app just returns to the main screen.

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And if I press back again, the app exits normally.

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Alright, so let's run the app again.

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We're gonna tap the plus icon

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and we're gonna rotate it to landscape.

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Because the main screen is showing the user,

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we'll probably expect to close the app.

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Of course you might disagree with this, and that's fine.

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If you want the screen to behave the same as portrait

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and just remove the fragment,

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then you can just remove the task for nTwoPane

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in our onBackPressed function.

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It's up to you how your app behaves.

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I'm sure you had achieved whatever you decide.

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Alright so let's tap back now to see what happens.

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And in our case, because of the way we've coded it,

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the app exits.

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And we should also make sure that

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we haven't broken the app button.

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So let's just run the app again.

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And tap on plus again.

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So the up button here in landscape doesn't quit,

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it just removes the fragment.

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Well it does what it should do, so let's confirm that.

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That's correct, it has done that.

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And let's go back to portrait.

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Plus, click on up, and it successfully removes the fragment

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and it doesn't try and exit.

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So up will remove the fragment as you saw

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and there's no further testing needed and

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that's because the up button's been removed from the toolbar

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in both landscape and portrait testing there.

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Alright so that's our up and back navigation

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finished for now.

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And we'll be looking at dialogues later,

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as I mentioned and giving the user a chance to confirm

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that they wanna quit but I'll stop this video here for now.

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The next step in our app is to save the data

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that the user's entered or changed.

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So it's time to start hitting the database.

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As I mentioned in the view model section,

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Google have now deprecated the loader classes.

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We'd originally used the loader to provide data

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for our main activity.

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Now we're going to use it to view model instead.

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When writing your apps, you'll often get to a point

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where something you wanna do relies

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on something you haven't written yet

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and that's the case here.

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Our view model class will take care of presenting the data

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to main activity as well as saving the changes.

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But we haven't written that yet.

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Obviously we can't present data to display

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if there isn't any saved in the database.

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So they get around that.

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I'm going to get the edited fragment to save the data.

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This is only temporary.

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And we'll be moving the code into the view model

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but it's quite common to do things like this.

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If we put the code that saves the task into its own function

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moving it shouldn't result in not too many changes

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when we get to that stage of moving it.

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So that's what we'll do

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and we'll start work on that in the next video.