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

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

Do you remember the parcelable interface?

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

more complex data around in a standard way.

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

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

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

the artist ,the year released and more.

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

Now we could break this down piece by piece and

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

hopefully you see that that could quickly get cumbersome and

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

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

Let's start by looking at the layout.

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

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

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

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

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

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

a text view which will show the title.

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

Icon pack which is a really useful set of artwork.

You can even download individual icons from right here

by clicking on the one that you want.

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

download in different formats.

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

future reference.

Now let's open up a recycler view adapter.

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

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

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

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

We have a view holder down here called SongViewHolder.

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

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

an onClick method.

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

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

Let's start by declaring an explicit intent.

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

Now normally in an activity the context is readily available.

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

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

we're storing it as mContext.

So, let's use that.

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

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

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

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

Actually, the original

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

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

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

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

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

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

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

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

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

We can access this from mSongs,

which is an array with a method called getAdapterPosition.

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

item is being acted on.

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

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

Mainactivity.EXTRA_LIST_POSITION.

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

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

Let's see what happens.

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

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

Once again back in playlist adapter.

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

Finally we need to start the detail activity.

So let's call startActivity and

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

Remember the startActivity methods are in the activity class but

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

So, do we know what that is from here?

We do. We are passing in the context when

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

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

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

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

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

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

MainActivity.RequestFavorite.