Showing a user's contacts in the form of a list is a fine idea. It's functional, looks all right, and people are used to seeing data displayed in the form of a list. However, wouldn't it be nice if there was a more interesting way to display the same contact data? For instance, using bigger images for the contact photos. And instead of showing everything in a list, maybe a grid is a nice alternative.

Exciting and compelling layouts drive user engagement. Users enjoy interacting with well-designed apps, and they certainly notice when you put in a bit of extra effort. Of course, merely implementing a grid layout won't automatically make your app great but when used well, users can certainly feel more at home with your app than they would if you just stick to a table view. Every app benefits from a different kind...

When you use a standard collection view, it uses a grid layout. In this grid layout, all items are evenly spaced, and all items have the same size. You can visualize this quite easily by giving the collection view cell a background color in your Storyboard and running your app. This standard grid layout makes adding a grid to your app a breeze. However, the standard implementation of the grid layout is not quite perfect. If you look at the grid you have set up, it should look good on, for instance, an iPhone 8 but when switching to a smaller screen such as the iPhone SE, the layout looks nothing like the beautiful grid layout you saw before. Viewing the grid on a larger screen such as an iPhone 8 Plus doesn't make it any better either. The grid would be significantly improved if every cell was sized based...

You have probably already noticed that, apart from the ability to add a custom layout, a collection view is very similar to a table view. When you look at what collection view does under the hood to maintain excellent scrolling performance, you will find even more similarities. The collection view is optimized to show as many cells on screen as quickly as it possibly can while keeping its memory footprint as small as possible. These optimizations are important for table views but they are even more important for collection views because a collection view might show a lot more cells on screen at a time than a table view does. The following diagram visualizes this:

The fact that collection views show so many cells at once has made it so that Apple added an extra optimization to it compared to table views. A table view always loads one or two items that...

In the previous chapter, you saw how to implement several interactions with a table view by implementing several of its delegate methods. Any time the user interacts with a cell, the table view calls a delegate method to see what exactly should happen as a response to this interaction. Collection views have incredibly similar capabilities, except for a few details. For instance, implementing reordering on a collection view requires a little bit more work than it does for a table view, as you will see shortly. Also, collection view cells cannot be swiped on to reveal actions to, for instance, delete a cell like you can with a table view cell. Similar functionality can be added to collection views though, and this section will show you exactly how.

You will learn how to implement the following interactions:

• Cell selection
• Cell...

This chapter has taught you how to harness the powers given to you by UICollectionView and UICollectionViewLayout in your apps. You saw that collection view come with a nice grid layout out of the box and that you can easily customize this grid layout by implementing a couple of delegate methods. Next, you created your layout to make your contacts app look more interesting and engaging. You also learned about the collection view's performance characteristics and how to implement great features such as contact selection, deletion, and reordering.

You have learned some fairly complex matter in this chapter, and you have implemented some pretty advanced features, such as your custom layout, gesture recognition, and using animations to provide feedback to users. All of these techniques are important parts of your toolbox as an iOS developer because they are applicable...

1. UICollectionView is very similar to another component on iOS. Which component is this?

a) UIImageView 
b) UIScrollView
c) UITableView

2. Which class did you have to subclass to create your own collection view layout?

a) UICollectionViewFlowLayout
b) UICollectionViewLayout
c) UICollectionLayout

3. Which technique is applied by collection views to ensure great performance?

a) Fetching cells a couple of rows ahead of the user's current position
b) Fetching all cells at once
c) Fetching cells just in time

4. Where in Interface Builder can you find the collection view's layout object?

a) The Attributes Inspector
b) The Document Outline
c) The Object Library

5. Which feature that can be implemented for collection views is not available for table views?

a) Reordering cells
b) Deleting cells
c) Horizontal scrolling

6. What is a gesture recognizer?

a) An...

• Apple's documentation on UICollectionView: https://developer.apple.com/documentation/uikit/uicollectionview
• Apple's documentation UICollectionViewLayout: https://developer.apple.com/documentation/uikit/uicollectionviewlayout