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Investigating the Code6:02 with Ben Deitch
In this video we'll finish learning how the app works!
We've got a pizza object and a topping object. 0:00 And when the app is created we use the toppings list 0:03 to generate our topping bitmaps. 0:06 With that out of the way let's move on to the activities. 0:09 We've got main activity, which was the list of pizzas. 0:12 And creator activity, which let's us customize the pizzas. 0:16 Let's start with main activity. 0:20 At the top of the file, we've got a pizza ID constant. 0:23 Other than that, we just find the recyclerview. 0:27 Give it a layout manager, and set it up with an adapter. 0:32 If you've not seen something like this before, don't worry. 0:37 It's just an anonymous function stored in a variable. 0:41 So launch creator activity is a function that takes in an integer 0:45 which might be null and when this function runs, it will create an intent, 0:51 add the pizza ID to the intent and then start creator activity. 0:57 So, let's jump into Main Adapter and start from the top. 1:05 You can use Cmd or CTRL+B to jump to a class from its usage. 1:09 First, we've got our LaunchCreatorActivity function as the only parameter. 1:14 And as we just saw it takes an integer that might be null and returns nothing. 1:19 From here, we have a list of pizzas which will contain the pizzas 1:25 to display on the screen. 1:29 Each row in this RecyclerView will use the pizza row layout. 1:31 If we take a look at that layout, under Resources and the Layout directory. 1:39 We can see that it contains a text view for the name of the pizza, 1:45 a create new pizza button and a divider line at the bottom. 1:49 So instead of using multiple views for the pizza rows and 1:55 the create new pizza button, we just used this one view and we'll hide the elements 1:58 we don't need depending on whether we wanna show the pizza or the button. 2:04 Getting back to the adapter, let's move onto the view holder. 2:09 Back in the code we can see that the item count is one more than the size of 2:13 the list, this is to account for the new pizza button at the bottom. 2:18 Moving on to the view holder, we show or 2:23 hide the views depending on which type of row it is. 2:26 So, if it's not the last item in the list, we'll hide the button and if it is 2:30 the last item in the list, we'll make the button visible and hide everything else. 2:35 We also set up the on click listeners to call through to our 2:41 launch creator activity function. 2:43 If it's a pizza row that was clicked, we'll pass in the ID of the pizza. 2:46 And if the new pizza button was clicked, we'll just pass in null. 2:53 So regardless of which row we click, we'll end up launching CreatorActivity. 2:57 Let's hop over to CreatorActivity and see where we go from here. 3:03 Let me give us just a little more room here as well. 3:10 Let me just hide it instead. 3:15 At the top of CreatorActivity we create a pizza ID variable and 3:19 lateinit it another variable named pizzaView. 3:24 In Cotland, when you create a variable you have to give it a value. 3:28 But with lateinit, we can get around that. 3:32 We just need to make sure it gets initialized before we use it. 3:35 Speaking of PizzaView, let's take a quick detour of the PizzaView class. 3:39 Remember, Cmd or Ctrl+B on the class name will jump us into the class. 3:45 PizzaView is a custom view, meaning it extends from View that draws a pizza. 3:51 It starts by drawing a big circle for the crust. 3:57 Then it draws a smaller circle for the body of the pizza. 4:01 And finally draws each of the toppings on top. 4:05 To tell it which toppings to draw, we pass in a map of toppings to Booleans. 4:10 If a topping is paired with the value of true, we draw it. 4:16 Otherwise we don't and that's about all we need to know about the PizzaView class. 4:19 Though, feel free to pause me and 4:25 look through the rest of this code if you'd like. 4:26 Getting back to CreatorActivity and the onCreate method, 4:30 we retrieve the Pizza ID from the intent and 4:36 initialize our PizzaView to an empty pizza, by passing in an empty map. 4:39 Later on when we have some data, we'll update this map to not be empty. 4:45 From here we add our PizzaView to the frameLayout at the top of the screen and 4:50 set up our recyclerView that lives at the bottom. 4:55 To finish out CreatorActivity, 4:58 we've got a couple methods to set up the menu at the top of the screen. 5:00 On create options menu, creates the menu and 5:05 on options item selected is where we add functionality to the menu items. 5:08 The last class we need to look at is CreatorAdaptor. 5:13 This class manages the recyclerView at the bottom of CreatorActivity. 5:21 And as a parameter, it takes in a pizza view. 5:26 With this pizza view at the bottom, when a switch is checked, 5:29 we update the toppings mapping with the state of the switch and 5:35 tell the pizza view to update by calling the invalidate method. 5:38 Awesome we've now got a good understanding of the app, and 5:43 are ready to implement that resistance, I know that was a lot to cover. 5:46 But don't worry, from here on out we'll be taking things one step at at time. 5:50 And if you want to spend some more time playing around and 5:55 getting comfortable with the app, please do. 5:57 I'll be here waiting for you when you get back. 5:59
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