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All right, so
we can pass simple data back and forth.

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We've actually seen how to pass complex
data around in an earlier course too.

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Do you remember the parcelable interface?

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It's a specific type of
serialization that allows us to pass

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more complex data around
in a standard way.

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Let's look at an example here with
complex data and a recycler view.

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In the project, we have eight models
package, and inside is a song class.

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It contains a bit of information
about a specific song like,

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the artist ,the year released and more.

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The goal here is to transfer an instance
of a song from one activity to another.

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Now we could break this
down piece by piece and

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attach each of these pieces of data
as separate extras to one intent, but

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hopefully you see that that
could quickly get cumbersome and

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also potentially impossible as our
models get more and more complex.

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Next, let's take a look at the recycler
view used in main activity.

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Let's start by looking at the layout.

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If we expand rez, then layout,
and open activity_main,

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here we can see a list of
items above our buttons, and

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here in the text view, we can see
we're using the recyclerView element.

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The Recycler View uses list item song for
individual items, and in here

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we have an image view, which will show
a heart icon when a song is favorited.

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It's hidden by default, which is
why we don't see it over here, and

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a text view which will show the title.

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By the way, I got this heart icon
from the Google material design.

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Icon pack which is a really
useful set of artwork.

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You can even download individual
icons from right here

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by clicking on the one that you want.

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You can change the density,
you can change the color and

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download in different formats.

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I put the link in teachers notes and
I'd recommend bookmarking it for

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future reference.

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Now let's open up a recycler view adapter.

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We have an adapters package and
inside is a playlist adapter.

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Recycler views get a little
tricky when it comes to TAPS and

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intents and results, because if you
remember, the best practice for

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recycler views is to define a view
holder that binds the data to each item.

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We have a view holder down
here called SongViewHolder.

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This means that taps are detected in
code is triggered from each view holder,

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which we see down here we have bind
song which binds it to the view and

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an onClick method.

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Let's add the code to send a whole song
to the detail view to see what I mean.

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I'm going to add a few lines to bump up my
code and then here in the onClick method.

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Let's start by declaring
an explicit intent.

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Intent equals new intent and
we'll pass in the context.

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Now normally in an activity
the context is readily available.

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Here we need to make
sure that it's passed in.

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We're passing it in when we
create the playlists adapter and

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we're storing it as mContext.

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So, let's use that.

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We want to go to the Detailactivity-class,
and next we want to put

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the whole song as an extra intent
that put extra, check up this list it

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includes a put extra overload that takes a
parcelable value as one of its parameters.

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So let's use for the first parameter
the existing key mainActivity.EXTRA_SONG.

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Actually, the original

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key from the original version of this
project is slightly different key.

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So let's fix that real quick so
that we're consistent.

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So go to main_activity, and
up at the top select KEY_SONG.

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Right-click and select Refactor > Rename
we want our keys to be consistent.

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While it doesn't really
matter what we name our keys,

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it helps to have a consistent format,
so let's call this extra song, and

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let's also change the value so that
it's consistent will repeat extra _SONG.

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Okay, so back in playlist adapter,
we can now access this extra song, and

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now we can parcel in the song
at the current position.

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We can access this from mSongs,

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which is an array with a method
called getAdapterPosition.

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One tricky thing about recycler views is
letting the parent activity know which

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item is being acted on.

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We're going to need that position, so
let's just add it as another extra.

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Intent.putExtra and we need another key,
let's define it here.

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Mainactivity.EXTRA_LIST_POSITION.

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Now if we hover over this,
and let's try quick fix.

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If we hit alt plus enter, we can create
a new constant field extra list position.

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Let's see what happens.

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Look at that,
it's got pretty much everything we need.

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Let's just come over here and type in our
value EXTRA_LIST_POSITION, very nice.

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Once again back in playlist adapter.

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Now we can pass in the position by
calling getAdapterPosition once again.

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Finally we need to start
the detail activity.

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So let's call startActivity and

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wait a minute, why is an auto
complete showing anything here?

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Remember the startActivity methods
are in the activity class but

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this is an adapter class,
we need to reference the parent activity.

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So, do we know what that is from here?

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We do.
We are passing in the context when

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we create this adapter, and we're storing
it in mContext, we could change that to

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pass in an activity explicitly, but
let's just do it with a cast here.

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So add some parentheses,
notice there's double parentheses.

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And we're going to cast to Activity,
it's mContext, and with the second

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set of run the C's, we can now use the
.syntax to call start activity for result.

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We'll pass in our intent, and we'll
use a request code the same as before

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MainActivity.RequestFavorite.