Layer behavior (implicit animation), layer behavior

Layer behavior (implicit animation), layer behavior
Layer behavior

Now let's make an experiment and try to directly animation the layers associated with UIView instead of a separate layer. Listing 7.4 is a slight modification to listing 7.2 code, removedcolorLayerAnd directly setlayerViewThe background color of the associated layer.

Listing 7.4 directly sets the properties of a Layer

 1 @interface ViewController () 2  3 @property (nonatomic, weak) IBOutlet UIView *layerView; 4  5 @end 6  7 @implementation ViewController 8  9 - (void)viewDidLoad10 {11     [super viewDidLoad];12     //set the color of our layerView backing layer directly13     self.layerView.layer.backgroundColor = [UIColor blueColor].CGColor;14 }15 16 - (IBAction)changeColor17 {18     //begin a new transaction19     [CATransaction begin];20     //set the animation duration to 1 second21     [CATransaction setAnimationDuration:1.0];22     //randomize the layer background color23     CGFloat red = arc4random() / (CGFloat)INT_MAX;24     CGFloat green = arc4random() / (CGFloat)INT_MAX;25     CGFloat blue = arc4random() / (CGFloat)INT_MAX;26     self.layerView.layer.backgroundColor = [UIColor colorWithRed:red green:green blue:blue alpha:1.0].CGColor;27     //commit the transaction28     [CATransaction commit];29 }

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Run the program and you will find that when you press the button, the layer color instantly switches to the new value, instead of the previous smooth transition animation. What happened? Implicit animation seems to beUIViewThe associated layer is disabled.

Imagine ifUIViewIf all attributes have animation properties, we should be able to notice when we modify them. Therefore, if UIKit is built on Core Animation (Animation for everything by default), how can implicit Animation be disabled by UIKit?

We know that Core Animation usually correspondsCALayerAll attributes (animation attributes)UIViewDisable the feature of the layer associated with it. To better illustrate this, we need to know how implicit animation is implemented.

When we change the attributeCALayerThe animation automatically applied is calledAction, WhenCALayerWhen the attribute of is modified, it will call-actionForKey:Method to pass the attribute name. The remaining operations areCALayerThe header file is described in detail as follows:

• The layer first checks whether it has delegation and whether it is implemented.CALayerDelegateProtocol-specified-actionForLayer:forKeyMethod. If yes, call and return the result.
• If there is no delegate, or the delegate is not implemented-actionForLayer:forKeyMethod, the layer then checksactionsDictionary.
• IfActions dictionaryThe layer does not contain the corresponding attributes.styleThe dictionary then searches for the attribute name.
• Finally, ifstyleThe corresponding behavior cannot be found, so the layer will directly call-defaultActionForKey:Method.

So after a complete search,-actionForKey:Either return NULL (in this case, no animation will occur) orCAActionThe object corresponding to the Protocol.CALayerUse this result to animation previous and current values.

This explains how UIKit disables implicit Animation: eachUIViewEach layer associated with it plays a delegate and provides-actionForLayer:forKey. When not implementing an animation block,UIViewReturns the behavior of all layers.nilBut within the animation block range, it returns a non-null value. We can use a demo to do a simple experiment (listing 7.5)

Listing 7.5actionForLayer:forKey:Implementation

 1 @interface ViewController () 2  3 @property (nonatomic, weak) IBOutlet UIView *layerView; 4  5 @end 6  7 @implementation ViewController 8  9 - (void)viewDidLoad10 {11     [super viewDidLoad];12     //test layer action when outside of animation block13     NSLog(@"Outside: %@", [self.layerView actionForLayer:self.layerView.layer forKey:@"backgroundColor"]);14     //begin animation block15     [UIView beginAnimations:nil context:nil];16     //test layer action when inside of animation block17     NSLog(@"Inside: %@", [self.layerView actionForLayer:self.layerView.layer forKey:@"backgroundColor"]);18     //end animation block19     [UIView commitAnimations];20 }21 22 @end

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Run the program. The console displays the following results:

1 $ LayerTest[21215:c07] Outside: <null>2 $ LayerTest[21215:c07] Inside: <CABasicAnimation: 0x757f090>

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So we can predict that when the attribute changes outside the animation block,UIViewDirectly returnnilTo disable implicit animation. However, if the corresponding attributes are returned Based on the animation type within the animation block range, in this exampleCABasicAnimation(As mentioned in chapter 8 "Explicit Animation ).

Certainly returnnilIt is not the only way to disable implicit animation,CATransacitionThere is a method called+setDisableActions:To enable or disable implicit animation for all attributes. If[CATransaction begin]Then add the following code to prevent the animation from occurring:

[CATransaction setDisableActions:YES];

To sum up, we know the following points:

• UIViewImplicit animation is disabled for the associated layers. The only way to do animation for this layer is to useUIViewInstead of relying onCATransaction), Or inheritUIViewAnd Overwrite-actionForLayer:forKey:Method, or directly create an explicit animation (for details, see Chapter 8 ).
• For an independent layer, we can implement-actionForLayer:forKey:Delegate method, or provideactionsDictionary to control implicit animation.

Let's use a different behavior for the color gradient example.colorLayerSet a customactionsDictionary. We can also use Delegation for implementation,actionsDictionary can write less code. So how can we create a suitable behavior object?

The behavior is usually caused by Core Animation.ImplicitCalledExplicitAnimation object. Here we use an implementationCATransactionInstance, calledAdvance transition.

The transition will be explained in detail in Chapter 8.CATransitionResponseCAActionProtocol, and can be used as a layer action. The results are very good. No matter when the background color is changed, the new color block slides in from the left side, rather than the default gradient effect.

Listing 7.6 custom Behaviors

1 @ interface ViewController () 2 3 @ property (nonatomic, weak) IBOutlet UIView * layerView; 4 @ property (nonatomic, weak) IBOutlet CALayer * colorLayer; /* the enthusiastic person finds that this should be changed to @ property (nonatomic, strong) CALayer * colorLayer; otherwise, the running result is incorrect. 5 */6 7 @ end 8 9 @ implementation ViewController10 11-(void) viewDidLoad12 {13 [super viewDidLoad]; 14 15 // create sublayer16 self. colorLayer = [CALayer layer]; 17 self. colorLayer. frame = CGRectMake (501_f, 501_f, 1001_f, 1001_f); 18 self. colorLayer. backgroundColor = [UIColor blueColor]. CGColor; 19 // add a custom action20 CATransition * transition = [CATransition animation]; 21 transition. type = kCATransitionPush; 22 transition. subtype = kCATransitionFromLeft; 23 self. colorLayer. actions =@{@ "backgroundColor": transition}; 24 // add it to our view25 [self. layerView. layer addSublayer: self. colorLayer]; 26} 27 28-(IBAction) changeColor29 {30 // randomize the layer background color31 CGFloat red = arc4random ()/(CGFloat) INT_MAX; 32 CGFloat green = arc4random () /(CGFloat) INT_MAX; 33 CGFloat blue = arc4random ()/(CGFloat) INT_MAX; 34 self. colorLayer. backgroundColor = [UIColor colorWithRed: red green: green blue: blue alpha: 1.0]. CGColor; 35} 36 37 @ end38

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