ios - Core animation progress callback

Question

Is there an easy way to be called back when a Core Animation reaches certain points as it's running (for example, at 50% and 66% of completion ?

I'm currently thinking about setting up an NSTimer, but that's not really as accurate as I'd like.

Answer 1

我终于为这个问题开发了一个解决方案。

本质上，我希望每一帧都被召回并做我需要做的事情。

没有明显的方法可以观察动画的进度，但实际上是可能的：

• 首先，我们需要创建一个新的 CALayer 子类，它有一个名为“progress”的动画属性。

• 我们将图层添加到我们的树中，然后创建一个动画，该动画将在动画持续时间内将进度值从 0 驱动到 1。

• 由于我们的进度属性可以设置动画，因此动画的每一帧都会在我们的子类上调用 drawInContext。这个函数不需要重绘任何东西，但是它可以用来调用一个委托函数:)

这是类接口：

@protocol TAProgressLayerProtocol <NSObject>

- (void)progressUpdatedTo:(CGFloat)progress;

@end

@interface TAProgressLayer : CALayer

@property CGFloat progress;
@property (weak) id<TAProgressLayerProtocol> delegate;

@end

和实施：

@implementation TAProgressLayer

// We must copy across our custom properties since Core Animation makes a copy
// of the layer that it's animating.

- (id)initWithLayer:(id)layer
{
    self = [super initWithLayer:layer];
    if (self) {
        TAProgressLayer *otherLayer = (TAProgressLayer *)layer;
        self.progress = otherLayer.progress;
        self.delegate = otherLayer.delegate;
    }
    return self;
}

// Override needsDisplayForKey so that we can define progress as being animatable.

+ (BOOL)needsDisplayForKey:(NSString*)key {
    if ([key isEqualToString:@"progress"]) {
        return YES;
    } else {
        return [super needsDisplayForKey:key];
    }
}

// Call our callback

- (void)drawInContext:(CGContextRef)ctx
{
    if (self.delegate)
    {
        [self.delegate progressUpdatedTo:self.progress];
    }
}

@end

然后我们可以将该层添加到我们的主层：

TAProgressLayer *progressLayer = [TAProgressLayer layer];
progressLayer.frame = CGRectMake(0, -1, 1, 1);
progressLayer.delegate = self;
[_sceneView.layer addSublayer:progressLayer];

并将其与其他动画一起制作动画：

CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:@"progress"];
anim.duration = 4.0;
anim.beginTime = 0;
anim.fromValue = @0;
anim.toValue = @1;
anim.fillMode = kCAFillModeForwards;
anim.removedOnCompletion = NO;

[progressLayer addAnimation:anim forKey:@"progress"];

最后，随着动画的进行，代理会被回调：

- (void)progressUpdatedTo:(CGFloat)progress
{
    // Do whatever you need to do...
}

Answer 2

如果您不想破解 CALayer 向您报告进度，还有另一种方法。从概念上讲，您可以使用 CADisplayLink 来保证每帧的回调，然后简单地测量自动画开始以来经过的时间除以持续时间来计算完成百分比。

开源库INTUAnimationEngine将此功能非常干净地打包到一个 API 中，该 API 看起来几乎与基于块的 UIView 动画一模一样：

// INTUAnimationEngine.h

// ...

+ (NSInteger)animateWithDuration:(NSTimeInterval)duration
                           delay:(NSTimeInterval)delay
                      animations:(void (^)(CGFloat percentage))animations
                      completion:(void (^)(BOOL finished))completion;

// ...

您需要做的就是在启动其他动画的同时调用此方法，为duration和传递相同的值delay，然后对于动画的每一帧，animations块将以当前完成百分比执行。如果您希望您的时间完全同步，您可以放心，您可以完全从 INTUAnimationEngine 驱动您的动画。

Answer 3

我在接受的答案中对 tarmes 建议的 CALayer 子类进行了 Swift (2.0) 实现：

protocol TAProgressLayerProtocol {

    func progressUpdated(progress: CGFloat)

}

class TAProgressLayer : CALayer {

    // MARK: - Progress-related properties

    var progress: CGFloat = 0.0
    var progressDelegate: TAProgressLayerProtocol? = nil

    // MARK: - Initialization & Encoding

    // We must copy across our custom properties since Core Animation makes a copy
    // of the layer that it's animating.

    override init(layer: AnyObject) {
        super.init(layer: layer)
        if let other = layer as? TAProgressLayerProtocol {
            self.progress = other.progress
            self.progressDelegate = other.progressDelegate
        }
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        progressDelegate = aDecoder.decodeObjectForKey("progressDelegate") as? CALayerProgressProtocol
        progress = CGFloat(aDecoder.decodeFloatForKey("progress"))
    }

    override func encodeWithCoder(aCoder: NSCoder) {
        super.encodeWithCoder(aCoder)
        aCoder.encodeFloat(Float(progress), forKey: "progress")
        aCoder.encodeObject(progressDelegate as! AnyObject?, forKey: "progressDelegate")
    }

    init(progressDelegate: TAProgressLayerProtocol?) {
        super.init()
        self.progressDelegate = progressDelegate
    }

    // MARK: - Progress Reporting

    // Override needsDisplayForKey so that we can define progress as being animatable.
    class override func needsDisplayForKey(key: String) -> Bool {
        if (key == "progress") {
            return true
        } else {
            return super.needsDisplayForKey(key)
        }
    }

    // Call our callback

    override func drawInContext(ctx: CGContext) {
        if let del = self.progressDelegate {
            del.progressUpdated(progress)
        }
    }

}

Answer 4

移植到 Swift 4.2：

protocol CAProgressLayerDelegate: CALayerDelegate {
    func progressDidChange(to progress: CGFloat)
}

extension CAProgressLayerDelegate {
    func progressDidChange(to progress: CGFloat) {}
}

class CAProgressLayer: CALayer {
    private struct Const {
        static let animationKey: String = "progress"
    }

    @NSManaged private(set) var progress: CGFloat
    private var previousProgress: CGFloat?
    private var progressDelegate: CAProgressLayerDelegate? { return self.delegate as? CAProgressLayerDelegate }

    override init() {
        super.init()
    }

    init(frame: CGRect) {
        super.init()
        self.frame = frame
    }

    override init(layer: Any) {
        super.init(layer: layer)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.progress = CGFloat(aDecoder.decodeFloat(forKey: Const.animationKey))
    }

    override func encode(with aCoder: NSCoder) {
        super.encode(with: aCoder)
        aCoder.encode(Float(self.progress), forKey: Const.animationKey)
    }

    override class func needsDisplay(forKey key: String) -> Bool {
        if key == Const.animationKey { return true }
        return super.needsDisplay(forKey: key)
    }

    override func display() {
        super.display()
        guard let layer: CAProgressLayer = self.presentation() else { return }
        self.progress = layer.progress
        if self.progress != self.previousProgress {
            self.progressDelegate?.progressDidChange(to: self.progress)
        }
        self.previousProgress = self.progress
    }
}

用法：

class ProgressView: UIView {
    override class var layerClass: AnyClass {
        return CAProgressLayer.self
    }
}

class ExampleViewController: UIViewController, CAProgressLayerDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()

        let progressView = ProgressView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        progressView.layer.delegate = self
        view.addSubview(progressView)

        var animations = [CAAnimation]()

        let opacityAnimation = CABasicAnimation(keyPath: "opacity")
        opacityAnimation.fromValue = 0
        opacityAnimation.toValue = 1
        opacityAnimation.duration = 1
        animations.append(opacityAnimation)

        let progressAnimation = CABasicAnimation(keyPath: "progress")
        progressAnimation.fromValue = 0
        progressAnimation.toValue = 1
        progressAnimation.duration = 1
        animations.append(progressAnimation)

        let group = CAAnimationGroup()
        group.duration = 1
        group.beginTime = CACurrentMediaTime()
        group.animations = animations

        progressView.layer.add(group, forKey: nil)
    }

    func progressDidChange(to progress: CGFloat) {
        print(progress)
    }
}