iOS Animations

Question 1

Repeating animation

Answer 1

.repeat: Include this option to makes your animation loop forever.
.autoreverse: Include this option only in conjunction with .repeat; this option repeatedly plays your animation forward, then in reverse.”

Question 2

Animation easing

Answer 2

curveLinear: This option applies no acceleration or deceleration to the animation. The only time in this book you’ll use this option is in the final challenge of Chapter 3: “Transitions”.
.curveEaseIn: This option applies acceleration to the start of your animation.
.curveEaseOut: This option applies deceleration to the end of your animation.
.curveEaseInOut: This option applies acceleration to the start of your animation and applies deceleration to the end of your animation

Question 3

What is spring in animation?

Answer 3

Question 4

Spring attributes

Answer 4

usingSpringWithDamping: This controls the amount of damping, or reduction, applied to the animation as it approaches its final state. This parameter accepts values between 0.0 and 1.0. Values closer to 0.0 create a bouncier animation, while values closer to 1.0 create a stiff-looking effect. You can think of this value as the “stiffness” of the spring.

initialSpringVelocity: This controls the initial velocity of the animation. A value of 1.0 sets the initial velocity of the animation to cover the total distance in the span of one second. Bigger and smaller values will cause the animation to have more or less velocity, and will affect how the spring settles. Note however that the initial velocity is soon amended by the spring calculation, and the animation will always finish by the end of duration

Question 5

Create transition?

Answer 5

AddSubview, RemoveSubview

In contrast hidding, you don’t need to worry about setting up a container view to hide and show views. In this case, the transition uses the view itself as the animation container

Question 6

Replacing one view with another view with animation

Answer 6

Question 7

To what transitions are targeted?

Answer 7

Transitions are targeted towards adding, removing, and replacing views in the view hierarchy.

Question 8

What to “chain” animations?

Answer 8

use keyframes

Keyframe animations not only allow you to “chain” animations but also to “overlap” them, and group them in general in any way you wish.
Don’t forget all keyframe timing values are relative to the complete animation, whereas the API defining the complete sequence uses absolute time.”

Question 9

Animating constrains from IB

Answer 9

1. Create outlet
2. Change .constant property

Question 10

To animate the layout changes when you change layout programmatically

Answer 10

1. Make change
2. Call self.view.layoutIfNeeded() afterwards in animation closure

Question 11

If you hadn’t called layoutIfNeeded()

Answer 11

UIKit would have performed a layout anyway since you changed a constraint, which marked the layout as dirty.

Question 12

By calling layoutIfNeeded() from within the animation closure

Answer 12

you set the center and bounds of every view involved in the layout.

Question 13

Views vs. layers

Answer 13

Layers:

A layer is a model object - it exposes data properties and implements no logic. It has no complex Auto Layout dependencies nor does it handle user interactions.

It has pre-defined visible traits - these traits are a number of data properties that affect how the contents is rendered on screen, such as border line, border color, position and shadow.

Core Animation optimizes the caching of layer contents and fast drawing directly on the GPU.

Views:

Complex view hierarchy layouts, Auto Layout, etc.

User interactions.

Often have custom logic or custom drawing code that executes on the main thread on the CPU.

Very flexible, powerful, lots of classes to subclass

Layers:

Simpler hierarchy, faster to resolve layout, faster to draw.

No responder chain overhead.

No custom logic by default. and drawn directly on the GPU.

Not as flexible, fewer classes to subclass.

Question 14

If you need to choose between views and layers here is a tip:

Answer 14

Choose view animations any time you can to do the job; you will know when you need more performance or flexibility and have to switch to layer animations instead.

Question 15

Animating the position, size, or transform of a layer equally affects

Answer 15

any view contained within that layer, just as if you had directly animated the view itself.

Question 16

What I can animate with CGLayer?

Answer 16

Shadow
Contents
Border
Position and size

Subclasses of CALayer usually have other properties that you can animate

Question 17

Animation objects in Core Animation are

Answer 17

simply data models; you create an instance of the model and set its data properties accordingly

Since layer animations are data models that are copied by Core Animation when added to a layer, you can reuse the same model instance to create a number of similar animations and even adjust some of its properties in between adding it to different layers.

Question 18

An instance of CABasicAnimation describe

Answer 18

a potential layer animation: one that you might choose to run now, at a later time, or not at all. Since the animation isn’t bound to a specific layer, you can re-use the animation on other layers and each layer will run a copy of the animation independently. In an animation model you can specify the property to animate as the keypath argument; that’s convenient, as you’ll always be animating something in the layer.

A CABasicAnimation object is just a data model, which is not bound to any particular layer

CABasicAnimation is a basic animation model class you use to describe the desired animation, which you hand off for rendering by calling CALayer.add(_, forKey:).

Question 19

What view.layer.add(flyRight (CABasicAnimation), forKey: nil) do?

Answer 19

add(_:forKey:) makes a copy of the animation object and tells Core Animation to run it on the layer. The key argument is for your use only; it lets you identify the animation later on if you need to change or stop the animation.

add(_:forKey:) makes a copy of the animation object.

Question 20

The fillMode property

Answer 20

The fillMode property lets you control the behavior of your animation at the beginning and end of its sequence.

Question 21

Presentation layer

Animations vs. real content

Answer 21

When you animate a text field, you’re not actually seeing the field itself animated; instead, you’re seeing a cached version of it known as the presentation layer. The presentation layer is removed from the screen once the animation completes and the original layer shows itself again.

Question 22

Leaving animations on the screen

Answer 22

affects performance

Question 23

Rule for completing and setting fillMode for layers animations

Answer 23

remove your animations and consider never using fillMode, except if the effect you want to achieve is not possible otherwise. fillMode makes your UI elements lose their interactivity and also makes the screen not reflect the actual values in your layer object.

Question 24

Rule for updating layer properties

Answer 24

Consider always doing that immediately after you add the animation to your layer.

Sometimes you might get the odd flash between the initial and final animation values.
In this case, try updating your layer property to the final animation value even before adding the animation.

Question 25

CGAnimationDelegate methods

Answer 25

You can set a delegate for your layer animations and be notified whenever the animations starts or finishes.CGAnimationDelegate methods

Question 26

How to know what layer call delegate method and get this layer?

Answer 26

Set name or even reference through KVO previously
flyRight.setValue(heading.layer, forKey: "layer")

Get layer: 
`let layer = anim.value(forKey: "layer") as? CALayer`

Question 27

What value(forKey:) in animation always return?

Answer 27

Remember that value(forKey:) always returns an AnyObject?; therefore you must cast the result to your desired type. Don’t forget that the cast operation can fail, so you must use optionals in the example above to handle error conditions, such as when the name key exists but the layer key does not.

Question 28

How to control the animation after it’s been started?

Answer 28

add(_:key:) has two parameters; so far, you’ve only been using the first to pass in the animation object itself.
The key parameter is a string identifier that lets you access and control the animation after it’s been started.

Question 29

If you need to synchronize animations on a layer, then you’ll need to use

Answer 29

*animation groups*to achieve this.

Question 30

How to get exactly animation what you want from layer?

Answer 30

myViewThatIWantToAnimate.layer.add(myBasicAnimation, forKey: "animationKey") - add key

The add(_, forKey:) API allows you to optionally specify a forKey string parameter to give the particular animation a name.

Animations are key-value coding compliant so you can attach arbitrary pieces of data to give you more information about the animation’s context.

Question 31

Get all animation keys

Answer 31

` guard let runningAnimations = info.layer.animationKeys()` - get key

Question 32

Once you know which animations are running, you can do several things with them: 3 things

Answer 32

1. Call removeAllAnimations() on the layer to stop all running animations or removeAnimation(forKey:) to remove just one.
2. Enumerate over the list of animations returned by animationKeys(). The animation
   objects are immutable, so you can’t modify the animation while they’re in progress.
3. Fetch an animation by key using animationForKey(_:). As before, the returned animation object will be immutable.