iOS Animations by Tutorials by 2019

Author:2019
Language: eng
Format: epub
Publisher: Ray Wenderlich

Intermediate keyframe animations

First you need to add the balloon image on screen. Open ViewController.swift, then add the following code to the bottom of login():

let balloon = CALayer() balloon.contents = UIImage(named: "balloon")!.cgImage balloon.frame = CGRect(x: -50.0, y: 0.0, width: 50.0, height: 65.0) view.layer.insertSublayer(balloon, below: username.layer)

In the code above, you create a new layer with the balloon image as its contents.

If you need to show an image on screen but don’t need all the benefits of using a UIView (such as Auto Layout constraints, attaching gesture recognizers and so forth), you can simply use a CALayer like in the code example above.

You position the layer near the top left corner, just outside of the visible area of the screen. Finally, you insert the layer below the username field so the balloon appears behind all the other elements in your form.

Now you can create the animation in few familiar steps. Add the following code underneath the previous code:

let flight = CAKeyframeAnimation(keyPath: "position") flight.duration = 12.0

Here you create a keyframe animation and set its duration to 12.0, the approximate duration of the faux authentication process.

Next, add the following key value points and times:

flight.values = [ CGPoint(x: -50.0, y: 0.0), CGPoint(x: view.frame.width + 50.0, y: 160.0), CGPoint(x: -50.0, y: loginButton.center.y) ].map { NSValue(cgPoint: $0) } flight.keyTimes = [0.0, 0.5, 1.0]

Note how you use map to neatly convert an array of points into an array of points boxed as NSValues. Ain’t Swift great?

This animates the balloon along the path that connects the three points you assigned to values, like so:

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