Switch statements are super-charged in Swift for iOS powered by Pattern Matching. This tutorial is part of an Intro to Swift series and includes a basic Intro to Storyboards.
Swift recognizes 7 different patterns: Wildcard, Identifier, Value-Binding, Tuple Pattern, Enumeration Case, Type-Casting, & Expression Pattern.
Here are few new tricks you can use in Swift:
#####(an example of the Expression Pattern)
You can provide a range as a case and Swift will determine whether or not the provided value is found within that range. Notice the use of ... for inclusive ranges and ..< for exclusive.
switch (value) {
case 1...4:
print("Catches values from 1 to 4")
case 5:
print("Catches exactly 5")
case 6..<10:
print("Catches values from 6 to 9")
default:
print("nothing")
}
Tuples allow you to match against several values and even types.
switch (chapter, page){
case ("Chapter One", 1):
print("First chapter, first page")
case ("Chapter One", 2):
print("First chapter, second page")
case ("Chapter Two", 1):
print("Second chapter, first page")
case ("Chapter Two", 2...5): //Tuples AND Ranges
print("Second chapter, & a page from 2 to 5")
default: ()
}
When a value of a tuple is a var or constant using let, Swift assigns the appropriate value to that variable for use in the case statement. Crazy business.
switch (button.tag, page){
case (1, 1):
print("First button, first page")
case (1, 2):
print("First button, second page")
//Here, we match on the tag of the button, and
//pass whatever the `index` is to the constant `x`
case (2, let x):
print("Second button, page number \(x)")
default: ()
}
One of the most common constraints is simply anchoring the various sides of a view to the edges of your UIViewController.view. In this example we anchor the Leading, Trailing, & Bottom edges of the button to the view, then we set the Height constraint. This will keep the button at the bottom, stretching across the full width of the view, but maintaining a constant height.
Our main logo/icon view will be centered horizontally. To do this, we have to set the Width and Height constraints as well. XCode won't be completely happy until we set the vertical constraint as well. We do this with a simple Top constraint to the top of the view.
You can connect multiple buttons to one @IBAction method. In our method, we're determining which button was tapped by matching the tag value we assigned it in the storyboard. That value is matched inside a tuple so we can also check which "page" we're on.
One way to change or animate UIViews that are constrained using autolayout is the animate the constraints themselves. Control-click and drag from the bottom constraint of the bottom button to create the reference. We'll refer to this later and move the button in and out of visibility based on the scrollView's scroll position.
As the user scrolls the scrollView, we check to see where the horizontal offset falls. The various page/section icons fade in and out depending on which "page" the user has scrolled to.
func scrollViewDidScroll(scrollView: UIScrollView) {
if prevButton != nil && nextButton != nil {
//Update the view based on the scrollView position
switch scrollView.contentOffset.x {
case 0:
prevButton.hidden = true;
case 0..<viewWidth:
prevButton.hidden = false;
prevButton.alpha = scrollView.contentOffset.x / viewWidth
//Fade Out
logoImageView.alpha = 1 - (scrollView.contentOffset.x / viewWidth)
//Fade In
userLabel.alpha = scrollView.contentOffset.x / viewWidth
case viewWidth..<viewWidth*2:
userLabel.alpha = 1 - (scrollView.contentOffset.x - viewWidth) / viewWidth
messageLabel.alpha = (scrollView.contentOffset.x - viewWidth) / viewWidth
case viewWidth*2..<viewWidth*3:
nextButton.hidden = false;
nextButton.alpha = 1 - (scrollView.contentOffset.x - viewWidth*2) / viewWidth
messageLabel.alpha = 1 - (scrollView.contentOffset.x - viewWidth*2) / viewWidth
sendLabel.alpha = (scrollView.contentOffset.x - viewWidth*2) / viewWidth
bottomButtonBottomConstraint.constant = -50 * (1 - (scrollView.contentOffset.x - viewWidth*2) / viewWidth)
case viewWidth*3:
nextButton.hidden = true;
default:
() //Do nothing in this case
//leaving this empty causes an error
}
//Update current index
currentIndex = Int(scrollView.contentOffset.x / viewWidth)
}
}
Tapping the "Prev" and "Next" buttons will cause the scrollView to scroll between pages. A swtch statement with Ranges and Tuples lets us intelligently map which actions are triggered by which button and when, allowing us to properly navigate forward and backward.
//Don't use 0 as a tag ID
@IBAction func navigate(sender: AnyObject) {
if sender.isKindOfClass(UIButton) {
let button = sender as! UIButton
currentIndex = Int(scrollView.contentOffset.x / viewWidth)
var newOffsetX:CGFloat = 0.0
switch (currentIndex, button.tag) {
case (1...4, 1):
newOffsetX = viewWidth * CGFloat(currentIndex - 1)
case (0...3, 2):
newOffsetX = viewWidth * CGFloat(currentIndex + 1)
default:
()
}
//Animate to scroll position
scrollView.setContentOffset(CGPointMake(newOffsetX, 0), animated: true)
}
}
If we properly wire up the Prev/Next buttons, anchoring them to the sides as well as the bottom button, properly center our logo/icons, and connect our buttons to the navigate: @IBAction, our demo app will properly lay itself out, transition on scroll, and navigate on button taps.
Additional Code: http://pastebin.com/drrym5N9