Parcelable Complex Data

All right, so we can pass simple data back and forth. 0:00 We've actually seen how to pass complex data around in an earlier course too. 0:03 Do you remember the parcelable interface? 0:07 It's a specific type of serialization that allows us to pass 0:09 more complex data around in a standard way. 0:12 Let's look at an example here with complex data and a recycler view. 0:15 In the project, we have eight models package, and inside is a song class. 0:20 It contains a bit of information about a specific song like, 0:25 the artist ,the year released and more. 0:28 The goal here is to transfer an instance of a song from one activity to another. 0:30 Now we could break this down piece by piece and 0:35 attach each of these pieces of data as separate extras to one intent, but 0:37 hopefully you see that that could quickly get cumbersome and 0:41 also potentially impossible as our models get more and more complex. 0:43 Next, let's take a look at the recycler view used in main activity. 0:48 Let's start by looking at the layout. 0:51 If we expand rez, then layout, and open activity_main, 0:52 here we can see a list of items above our buttons, and 0:57 here in the text view, we can see we're using the recyclerView element. 1:00 The Recycler View uses list item song for individual items, and in here 1:05 we have an image view, which will show a heart icon when a song is favorited. 1:09 It's hidden by default, which is why we don't see it over here, and 1:14 a text view which will show the title. 1:16 By the way, I got this heart icon from the Google material design. 1:19 Icon pack which is a really useful set of artwork. 1:23 You can even download individual icons from right here 1:25 by clicking on the one that you want. 1:28 You can change the density, you can change the color and 1:29 download in different formats. 1:33 I put the link in teachers notes and I'd recommend bookmarking it for 1:37 future reference. 1:39 Now let's open up a recycler view adapter. 1:41 We have an adapters package and inside is a playlist adapter. 1:44 Recycler views get a little tricky when it comes to TAPS and 1:49 intents and results, because if you remember, the best practice for 1:52 recycler views is to define a view holder that binds the data to each item. 1:55 We have a view holder down here called SongViewHolder. 2:00 This means that taps are detected in code is triggered from each view holder, 2:03 which we see down here we have bind song which binds it to the view and 2:07 an onClick method. 2:11 Let's add the code to send a whole song to the detail view to see what I mean. 2:14 I'm going to add a few lines to bump up my code and then here in the onClick method. 2:19 Let's start by declaring an explicit intent. 2:22 Intent equals new intent and we'll pass in the context. 2:26 Now normally in an activity the context is readily available. 2:31 Here we need to make sure that it's passed in. 2:35 We're passing it in when we create the playlists adapter and 2:37 we're storing it as mContext. 2:39 So, let's use that. 2:41 We want to go to the Detailactivity-class, and next we want to put 2:43 the whole song as an extra intent that put extra, check up this list it 2:49 includes a put extra overload that takes a parcelable value as one of its parameters. 2:55 So let's use for the first parameter the existing key mainActivity.EXTRA_SONG. 3:00 Actually, the original 3:06 key from the original version of this project is slightly different key. 3:08 So let's fix that real quick so that we're consistent. 3:12 So go to main_activity, and up at the top select KEY_SONG. 3:14 Right-click and select Refactor > Rename we want our keys to be consistent. 3:18 While it doesn't really matter what we name our keys, 3:25 it helps to have a consistent format, so let's call this extra song, and 3:28 let's also change the value so that it's consistent will repeat extra _SONG. 3:31 Okay, so back in playlist adapter, we can now access this extra song, and 3:37 now we can parcel in the song at the current position. 3:42 We can access this from mSongs, 3:44 which is an array with a method called getAdapterPosition. 3:46 One tricky thing about recycler views is letting the parent activity know which 3:52 item is being acted on. 3:55 We're going to need that position, so let's just add it as another extra. 3:57 Intent.putExtra and we need another key, let's define it here. 4:00 Mainactivity.EXTRA_LIST_POSITION. 4:07 Now if we hover over this, and let's try quick fix. 4:14 If we hit alt plus enter, we can create a new constant field extra list position. 4:17 Let's see what happens. 4:21 Look at that, it's got pretty much everything we need. 4:23 Let's just come over here and type in our value EXTRA_LIST_POSITION, very nice. 4:25 Once again back in playlist adapter. 4:32 Now we can pass in the position by calling getAdapterPosition once again. 4:33 Finally we need to start the detail activity. 4:39 So let's call startActivity and 4:41 wait a minute, why is an auto complete showing anything here? 4:44 Remember the startActivity methods are in the activity class but 4:47 this is an adapter class, we need to reference the parent activity. 4:51 So, do we know what that is from here? 4:55 We do. We are passing in the context when 4:57 we create this adapter, and we're storing it in mContext, we could change that to 4:59 pass in an activity explicitly, but let's just do it with a cast here. 5:03 So add some parentheses, notice there's double parentheses. 5:07 And we're going to cast to Activity, it's mContext, and with the second 5:09 set of run the C's, we can now use the .syntax to call start activity for result. 5:15 We'll pass in our intent, and we'll use a request code the same as before 5:20 MainActivity.RequestFavorite. 5:24