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G'day everyone, welcome back.

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In the last video, we saw how to use our AppDialog class

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to get the user to confirm that they
really do want to delete a record.

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I'll add the function to AddEditFragment,
just before saveTask, and call it isDirty.

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After creating a new task, using the taskFromUi
function that we used earlier,

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the function returns true, if the new task
doesn't equal a task that we're editing.

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In the case of adding a task, task will
be null and won't equal newTask.

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That can cause a problem,

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and the function deals with that by also checking
that the name and description aren't empty,

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and if the sort order has changed from the default of zero.

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Without those checks, we'd get the dialogue if we tried
to leave a new task, even if nothing had been typed.

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Try removing that second compound condition,
if you're not sure why it's necessary.

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If newTask and task are equal, the user hasn't
made any changes and the function returns false.

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Alright. Back in MainActivity, we can use that function
to decide whether to prompt the user or not.

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There are two places we need to do that,

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and it makes sense to create a function
to show the dialogue.

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I'm going to create it as a Kotlin extension function,
and I'll talk about them in the video after next.

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Create a new Kotlin file called ExtensionFunctions.

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Kotlin extension functions can be great if
you avoid the temptation to overuse them.

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I'll discuss what we're doing here,
once we've seen it working.

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The function's code is simple enough. It just puts the
required values into the bundle and creates a dialog.

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Something we haven't done before, is used
default values for the function arguments.

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That's something that Kotlin lets us do,
that you can't do in Java.

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If we just want the default, OK and cancel buttons, we don't
have to specify values for the positive and negative captions.

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The default values will be used automatically.

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You can find out more about them,
in the Kotlin language reference

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at https://kotlinlang.org/docs/reference/functions.html

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Alright, I'll add the code to call this function in MainActivity.

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As we've done before, create a constant to hold the dialog id.

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We'll be using the confirmation dialogue in two places.

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I'll deal with onOptionsItemSelected first.

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We need to comment out this line,
because we're going to replace it.

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We're being quite defensive here, checking to
make sure that the fragment is an AddEditFragment.

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At the moment, there's only one fragment that
could result in the Up button being displayed,

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but if we add another fragment in the future, and try to
cast it to be an AddEditFragment, we'll get an exception.

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If you're going to cast something to another type, then
it's a good idea to make sure it can be cast to that type.

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Note that Kotlin's performed a smart cast for us, once
we've checked that the fragment is the correct type.

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We've got a couple of errors because we
haven't created the string resources yet.

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I'll get the light bulb to create all three.

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The message resource will be called
cancelEditDiag_message.

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The positive caption will be called
cancelEditDiag_positive_caption,

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and the negative one will be
cancelEditDiag_negative_caption.

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It can take a couple of goes, sometimes, to get the
lightbulb to appear for the last two, because of the error.

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Click in the strings a couple of times if you need to,

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until you can select the extract string
resource option from the light bulb.

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We also have to remove the getString calls, because
we're passing the resource ID to the DialogFunction.

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We can use exactly the same code in the onBackPressed
function, so let's copy the entire if/else block,

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and paste it in place.

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Okay, I'll finish the video with a challenge.

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Have a go at that, and I'll see in the next video.