Swift - Display header with animation - swift

Question

I'm kinda new to Swift coding and I wanted to train myself by finding some layouts and try to implement them using AutoLayout.
Here is a screen shot of a screen I try to implement
https://i.imgur.com/9yzvnzp.png
The behaviour is wanted here is that on scrolling the picture should fade away and the title should be set like so
https://i.imgur.com/bLhyTGs.png
Could anybody help me on how am I supposed to do that ?
Should I use a ScrollView ? UITableView ? UICollectionView ?

Answer 1

I'm actually working on an application that does something similar.
So, the first thing you want to do is create a UIView for the background, i.e. the blue part that shows Squirtle. This view can take up the entire view controller. Connect it to your UIViewController via IBOutlet and call it backgroundView.
Next, we want to lay a UIScrollView over backgroundView. This scroll view should be constrained to the top, bottom, leading, and trailing edges of the superview so that it covers the entire view controller's frame. Connect this UIScrollView to your UIViewController via IBOutlet and name it scrollView. Also, make sure that scrollView's backgroundColor is set to clear. This way, we'll be able to see backgroundView underneath our scrollView.
Within your UIViewController, you'll want to set scrollView's delegate to self inside of viewDidLoad. Your UIViewController's code should now look something like this:
class SquirtleViewController: UIViewController {
#IBOutlet var backgroundView: UIView!
#IBOutlet var scrollView: UIScrollView!
override func viewDidLoad() {
super.viewDidLoad()
scrollView.delegate = self
}
}
extension SquirtleViewController: UIScrollViewDelegate {
}
We'll set delegate methods for scrollView later. These will help us know when the scroll view has begun scrolling to the top of our SquirtleViewController.
Now, our scrollView has a clear background, and doesn't actually display anything to our user. This is how we want it for now. We want the top of our scrollView to be clear so that we can see backgroundView behind it, and the bottom of our scrollView to have another view, i.e. the "content view" that shows STATS, EVOLUTIONS, MOVES, HP, etc.
So, let's add another UIView as a subview of our scrollView. Connect it to SquirtleViewController via IBOutlet and name it contentView.
Now, we need to create a constraint between contentView's top edge and scrollView's top edge. This constraint's constant needs to be equal to the height of backgroundView's content. This way, our contentView won't cover up what we want to see from backgroundView. We should also save this height as backgroundViewContentHeight so that we can reference it later.
We also need contentView's leading, trailing, and bottom constraints to be equal to those of its superview, i.e. scrollView. These do not need to be connected via IBOutlets.
Also, give contentView a height and width constraint and connect these as contentViewHeight and contentViewWidth respectively to SquirtleViewController via IBOutlet. This will help us set the contentSize of our scrollView later.
Your code should now look something like this:
class SquirtleViewController: UIViewController {
#IBOutlet var backgroundView: UIView!
#IBOutlet var scrollView: UIScrollView!
#IBOutlet var contentView: UIView!
//New lines of code
//Our constraints
#IBOutlet var contentViewTop: NSLayoutConstraint!
#IBOutlet var contentViewHeight: NSLayoutConstraint!
#IBOutlet var contentViewWidth: NSLayoutConstraint!
var backgroundViewContentHeight = 400
override func viewDidLoad() {
super.viewDidLoad()
scrollView.delegate = self
}
}
extension SquirtleViewController: UIScrollViewDelegate {
}
Now, when SquirtleViewController lays out its subviews, we are going to want to set the constant properties of contentViewHeight and contentViewWidth. This will set a contentSize for our scrollView. We want our contentViewWidth to simply be the size of our SquirtleViewController's view's width. Our contentViewHeight's constant will be a little different though, as it depends on the height of our contentView's subviews. For this example, we'll say the contentViewHeight's constant should be 1200. The code should now look like this:
class SquirtleViewController: UIViewController {
#IBOutlet var backgroundView: UIView!
#IBOutlet var scrollView: UIScrollView!
#IBOutlet var contentView: UIView!
//Our constraints
#IBOutlet var contentViewTop: NSLayoutConstraint!
#IBOutlet var contentViewHeight: NSLayoutConstraint!
#IBOutlet var contentViewWidth: NSLayoutConstraint!
var backgroundViewContentHeight = 400
override func viewDidLoad() {
super.viewDidLoad()
scrollView.delegate = self
}
//New lines of code
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
contentViewWidth.constant = view.frame.width
contentViewHeight.constant = 1200
}
}
extension SquirtleViewController: UIScrollViewDelegate {
}
From here, you can add subviews to backgroundView and contentView as you see fit in order to show the pokemon (backgroundView) as well as the pokemon's stats (contentView). But, you still need to know how to change the content of your backgroundView depending upon how much we have scrolled the scrollView. This is where the UIScrollViewDelegate helps us out.
There is a method in UIScrollViewDelegate that is called every time our scrollView's contentOffset.y changes. This basically means every time we change the amount that our scrollView has scrolled, this method will be called.
Inside of this method, we can cross reference the amount we've scrolled with the height of the background view. As our scrollView's contentOffset.y approaches the height of our backgroundView's content, we can fade out the image of Squirtle and fade in a UILabel that simply says "Squirtle" (like in your example).
So, in your case, I would suggest adding a UIImage of Squirtle as a subview of contentView and connect it via IBOutlet as pokemonImageView. pokemonImageView should have its frame partially outside of the contentView (like in your example). If you do this, ensure that contentView's clipsToBounds property is set to false.
I would also add a UILabel as a subview of backgroundView and connect it to SquirtleViewController via IBOutlet as pokemonNameLabel. When our SquirtleViewController's view loads, we should set pokemonNameLabel.alpha equal to zero so that it is initially hidden.
Your code should now look like this:
class SquirtleViewController: UIViewController {
#IBOutlet var backgroundView: UIView!
//New line of code
#IBOutlet var pokemonNameLabel: UILabel!
#IBOutlet var scrollView: UIScrollView!
#IBOutlet var contentView: UIView!
//New line of code
#IBOutlet var pokemonImageView: UIImageView!
//Our constraints
#IBOutlet var contentViewTop: NSLayoutConstraint!
#IBOutlet var contentViewHeight: NSLayoutConstraint!
#IBOutlet var contentViewWidth: NSLayoutConstraint!
var backgroundViewContentHeight = 400
override func viewDidLoad() {
super.viewDidLoad()
scrollView.delegate = self
//New line of code
pokemonNameLabel.alpha = 0
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
contentViewWidth.constant = view.frame.width
contentViewHeight.constant = 1200
}
}
extension SquirtleViewController: UIScrollViewDelegate {
}
Now we simply need to add the scrollViewDidScroll method inside of our class extension. This is the method that will tell us our scrollView's contentOffset.y property so that we know how much we've scrolled. As this number increases, our pokemonImageView's alpha should decrease to zero and our pokemonNameLabel's alpha should increase towards one.
Inside of this method, I would divide our scrollView.contentOffset.y by the height of our backgroundView minus the height of the pokemonNameLabel. We can then use this decimal to set our respective alphas of pokemonImageView and pokemonNameLabel.
Your code should now look something like this:
class SquirtleViewController: UIViewController {
#IBOutlet var backgroundView: UIView!
//New line of code
#IBOutlet var pokemonNameLabel: UILabel!
#IBOutlet var scrollView: UIScrollView!
#IBOutlet var contentView: UIView!
//New line of code
#IBOutlet var pokemonImageView: UIImageView!
//Our constraints
#IBOutlet var contentViewTop: NSLayoutConstraint!
#IBOutlet var contentViewHeight: NSLayoutConstraint!
#IBOutlet var contentViewWidth: NSLayoutConstraint!
var backgroundViewContentHeight = 400
override func viewDidLoad() {
super.viewDidLoad()
scrollView.delegate = self
//New line of code
pokemonNameLabel.alpha = 0
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
contentViewWidth.constant = view.frame.width
contentViewHeight.constant = 1200
}
}
extension SquirtleViewController: UIScrollViewDelegate {
func scrollViewDidScroll(_ scrollView: UIScrollView) {
//Subtracting contentView.frame.height from scrollView.frame.height
let alphaDecimal = scrollView.contentOffset.y / (backgroundViewContentHeight - pokemonNameLabel.frame.height)
pokemonNameLabel.alpha = alphaDecimal
pokemonImageView.alpha = 1 - alphaDecimal
}
}
Now, as we scroll up and what can be seen of the backgroundView shrinks, our pokemonImageView will fade out and our pokemonNameLabel will fade in. There will be a point in-between where both will have an alpha of 0.5. You can mess with this scrollViewDidScroll method as you see fit to make this work best for you.