- What are Fragments? 2:15
- My First Fragment 6:05
- Fragments? 5 questions
- Adding Fragments to Activities 4:13
- Adding a Fragment 2 objectives
- Making a List 8:56
- Checking It Twice 3:42
- Handling Clicks 5:20
- Handling Clicks 2 objectives
- Fragment Lifecycle 7:00
- Fragment Lifecycle 5 questions
- Keeping Track of Instance State 6:09
- Saving State 2 objectives
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Adding Fragments to Activities
4:13In this video we'll learn how to display our Fragment inside the placeholder ViewGroup!
We've just finished updating
our activities layout
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to have a placeholder view group for
our fragments.
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Now let's head over to MainActivity and
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use this placeholder to
display our new list fragment.
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Before we can display our list fragment,
it needs to exist.
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Let's create a new list fragment variable
at the bottom of the onCreate method.
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List fragment.
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Let's call it fragment = new ListFragment.
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Now that we've got our ListFragment,
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all we need to do is add this ListFragment
to our place holder view group.
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Let's start by creating a new fragment
manager variable named, fragment manager.
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Fragment manager.
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And make sure you're getting the one
from the Android.app package and
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not the one from the support package.
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Name it FragmentManager, and
then let's set it = getFragmentManager.
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[NOISE] The fragment
manager is an interface for
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interacting with our fragments.
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It helps us keep track of our fragments,
let's us manage the back stack of our
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fragments, and gives us access to
the fragment transactions A.P.I.
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which allows us to do things like add or
remove fragments.
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On the next line, let's create a new
fragment transaction variable and
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let's call it FragmentTransaction.
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Then let's set it =
fragmentManager.begintransaction.
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Then we see a warning
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that this transaction should be
completed with the commit call.
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So let's add two lines below here.
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And add that commit call
fragmentTransaction.commit.
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Fragment transactions are a lot
like shared preferences.
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Any changes won't be made permanent
until there's a call to commit.
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Back up on the line we skipped,
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let's finally add our list fragment
to our placeholder view group.
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Let's type fragmentTransaction.add,
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and for
the first parameter let's pass in our
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placeholder as the ID, R.id.placeholder.
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And for the second parameter,
let's pass in our fragment.
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Awesome.
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Now let's test the app and
see our fragment in action.
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Bummer.
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An error.
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Over in the log.
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It looks like we've got
an illegal state exception.
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The specified child already has a parent.
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You must call removeView on
the child's parent first.
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Okay, so where did this error occur?
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Nowhere, great.
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This might be a good time to talk about
why fragments can sometimes get a bad rap.
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There's just a lot of stuff to handle.
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On top of fragment managers and
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fragment transactions, fragments
themselves also have a life cycle.
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And the interplay between
the fragment life cycle and
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the activity life cycle can sometimes
leave you scratching your head, like here.
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To fix this error.
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we need to head over to
our list fragment class.
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Let's add a third parameter to
the inflate method and pass in false.
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The third parameter determines whether or
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not we attach this view to the view
group provided as the second parameter.
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It might seem weird that
we would set this to false
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when we actually do want to
attach to that view group.
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But when on Create view returns,
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our view will be automatically added to
the container view group by the system.
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So if we don't set this to false,
it'll be added twice and
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will get the error we saw earlier.
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Now that that's fixed,
let's run the app again.
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And there's our fragment.
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Nice.
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In the next video, we'll start making our
list fragment look a bit more list like.
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