Rewrite the API to use protocols

- Closes #69
- Closes #61
- Closes #22

Demo/demo/Main.storyboard

@@ -23,7 +23,7 @@
                                 <color key="textColor" red="0.99144423007965088" green="0.56549066305160522" blue="0.033751130104064941" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                                 <nil key="highlightedColor"/>
                             </label>
-                            <imageView clipsSubviews="YES" contentMode="scaleAspectFit" horizontalHuggingPriority="251" verticalHuggingPriority="251" placeholderIntrinsicWidth="600" placeholderIntrinsicHeight="300" translatesAutoresizingMaskIntoConstraints="NO" id="FSz-xF-Xds" customClass="AnimatableImageView" customModule="Gifu">
+                            <imageView clipsSubviews="YES" contentMode="scaleAspectFit" horizontalHuggingPriority="251" verticalHuggingPriority="251" placeholderIntrinsicWidth="600" placeholderIntrinsicHeight="300" translatesAutoresizingMaskIntoConstraints="NO" id="FSz-xF-Xds" customClass="GIFImageView" customModule="Gifu">
                                 <gestureRecognizers/>
                                 <constraints>
                                     <constraint firstAttribute="width" secondItem="FSz-xF-Xds" secondAttribute="height" multiplier="5:4" id="EOH-hn-KxM"/>

Demo/demo/classes/ViewController.swift

@@ -2,7 +2,7 @@ import UIKit
 import Gifu
 
 class ViewController: UIViewController {
-  @IBOutlet weak var imageView: AnimatableImageView!
+  @IBOutlet weak var imageView: GIFImageView!
 
   override func viewDidLoad() {
     super.viewDidLoad()
@@ -17,4 +17,3 @@ class ViewController: UIViewController {
     }
   }
 }
-

Gifu.xcodeproj/project.pbxproj

@@ -9,14 +9,17 @@
 /* Begin PBXBuildFile section */
 		0036ABB71BBD1D0B00C6CC3D /* mugen.gif in Resources */ = {isa = PBXBuildFile; fileRef = 0036ABB61BBD1D0B00C6CC3D /* mugen.gif */; };
 		0036ABB91BBD1D1400C6CC3D /* nailed.gif in Resources */ = {isa = PBXBuildFile; fileRef = 0036ABB81BBD1D1400C6CC3D /* nailed.gif */; };
-		005656ED1A6F14D6008A0ED1 /* Animator.swift in Sources */ = {isa = PBXBuildFile; fileRef = 005656EC1A6F14D6008A0ED1 /* Animator.swift */; };
+		005656ED1A6F14D6008A0ED1 /* FrameStore.swift in Sources */ = {isa = PBXBuildFile; fileRef = 005656EC1A6F14D6008A0ED1 /* FrameStore.swift */; };
-		005656EF1A6F1C26008A0ED1 /* AnimatableImageView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 005656EE1A6F1C26008A0ED1 /* AnimatableImageView.swift */; };
+		005656EF1A6F1C26008A0ED1 /* GIFImageView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 005656EE1A6F1C26008A0ED1 /* GIFImageView.swift */; };
 		007E08441BD95E6200883D0C /* ArrayExtension.swift in Sources */ = {isa = PBXBuildFile; fileRef = 007E08431BD95E6200883D0C /* ArrayExtension.swift */; };
+		00978B6C1D9C6D2A00A6575F /* Animator.swift in Sources */ = {isa = PBXBuildFile; fileRef = 00978B6B1D9C6D2A00A6575F /* Animator.swift */; };
+		00978B6E1D9FA99D00A6575F /* AnimatorDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 00978B6D1D9FA99D00A6575F /* AnimatorDelegate.swift */; };
 		009BD1391BBC7F6500FC982B /* GifuTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 009BD1381BBC7F6500FC982B /* GifuTests.swift */; };
 		009BD13B1BBC7F6500FC982B /* Gifu.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 00B8C73E1A364DA400C188E7 /* Gifu.framework */; };
 		009BD1441BBC93C800FC982B /* CGSizeExtension.swift in Sources */ = {isa = PBXBuildFile; fileRef = 009BD1431BBC93C800FC982B /* CGSizeExtension.swift */; };
 		00B8C75F1A364DCE00C188E7 /* ImageSourceHelpers.swift in Sources */ = {isa = PBXBuildFile; fileRef = 00B8C75C1A364DCE00C188E7 /* ImageSourceHelpers.swift */; };
 		00B8C7961A3650EE00C188E7 /* Gifu.h in Headers */ = {isa = PBXBuildFile; fileRef = 00B8C7951A3650EE00C188E7 /* Gifu.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		00BF42CC1D99A1DC00C6F28D /* GIFAnimatable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 00BF42CB1D99A1DC00C6F28D /* GIFAnimatable.swift */; };
 		EAF49C7F1A3A4DE000B395DF /* UIImageExtension.swift in Sources */ = {isa = PBXBuildFile; fileRef = EAF49C7E1A3A4DE000B395DF /* UIImageExtension.swift */; };
 		EAF49CB11A3B6EEB00B395DF /* AnimatedFrame.swift in Sources */ = {isa = PBXBuildFile; fileRef = EAF49CB01A3B6EEB00B395DF /* AnimatedFrame.swift */; };
 /* End PBXBuildFile section */
@@ -34,9 +37,11 @@
 /* Begin PBXFileReference section */
 		0036ABB61BBD1D0B00C6CC3D /* mugen.gif */ = {isa = PBXFileReference; lastKnownFileType = image.gif; name = mugen.gif; path = Demo/GIFs/mugen.gif; sourceTree = SOURCE_ROOT; };
 		0036ABB81BBD1D1400C6CC3D /* nailed.gif */ = {isa = PBXFileReference; lastKnownFileType = image.gif; name = nailed.gif; path = Demo/GIFs/nailed.gif; sourceTree = SOURCE_ROOT; };
-		005656EC1A6F14D6008A0ED1 /* Animator.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Animator.swift; sourceTree = "<group>"; };
+		005656EC1A6F14D6008A0ED1 /* FrameStore.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FrameStore.swift; sourceTree = "<group>"; };
-		005656EE1A6F1C26008A0ED1 /* AnimatableImageView.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AnimatableImageView.swift; sourceTree = "<group>"; };
+		005656EE1A6F1C26008A0ED1 /* GIFImageView.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = GIFImageView.swift; sourceTree = "<group>"; };
 		007E08431BD95E6200883D0C /* ArrayExtension.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ArrayExtension.swift; sourceTree = "<group>"; };
+		00978B6B1D9C6D2A00A6575F /* Animator.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Animator.swift; sourceTree = "<group>"; };
+		00978B6D1D9FA99D00A6575F /* AnimatorDelegate.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AnimatorDelegate.swift; sourceTree = "<group>"; };
 		009BD1361BBC7F6500FC982B /* GifuTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = GifuTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		009BD1381BBC7F6500FC982B /* GifuTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GifuTests.swift; sourceTree = "<group>"; };
 		009BD13A1BBC7F6500FC982B /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
@@ -45,6 +50,7 @@
 		00B8C7421A364DA400C188E7 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; name = Info.plist; path = ../Source/Info.plist; sourceTree = "<group>"; };
 		00B8C75C1A364DCE00C188E7 /* ImageSourceHelpers.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ImageSourceHelpers.swift; sourceTree = "<group>"; };
 		00B8C7951A3650EE00C188E7 /* Gifu.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = Gifu.h; sourceTree = "<group>"; };
+		00BF42CB1D99A1DC00C6F28D /* GIFAnimatable.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = GIFAnimatable.swift; sourceTree = "<group>"; };
 		EAF49C7E1A3A4DE000B395DF /* UIImageExtension.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UIImageExtension.swift; sourceTree = "<group>"; };
 		EAF49CB01A3B6EEB00B395DF /* AnimatedFrame.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AnimatedFrame.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
@@ -98,9 +104,12 @@
 		007E08421BD95C6100883D0C /* Classes */ = {
 			isa = PBXGroup;
 			children = (
-				005656EE1A6F1C26008A0ED1 /* AnimatableImageView.swift */,
 				EAF49CB01A3B6EEB00B395DF /* AnimatedFrame.swift */,
-				005656EC1A6F14D6008A0ED1 /* Animator.swift */,
+				00978B6B1D9C6D2A00A6575F /* Animator.swift */,
+				005656EC1A6F14D6008A0ED1 /* FrameStore.swift */,
+				00BF42CB1D99A1DC00C6F28D /* GIFAnimatable.swift */,
+				005656EE1A6F1C26008A0ED1 /* GIFImageView.swift */,
+				00978B6D1D9FA99D00A6575F /* AnimatorDelegate.swift */,
 			);
 			name = Classes;
 			sourceTree = "<group>";
@@ -293,11 +302,14 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
-				005656EF1A6F1C26008A0ED1 /* AnimatableImageView.swift in Sources */,
+				005656EF1A6F1C26008A0ED1 /* GIFImageView.swift in Sources */,
-				005656ED1A6F14D6008A0ED1 /* Animator.swift in Sources */,
+				00978B6E1D9FA99D00A6575F /* AnimatorDelegate.swift in Sources */,
+				00BF42CC1D99A1DC00C6F28D /* GIFAnimatable.swift in Sources */,
+				005656ED1A6F14D6008A0ED1 /* FrameStore.swift in Sources */,
 				009BD1441BBC93C800FC982B /* CGSizeExtension.swift in Sources */,
 				EAF49CB11A3B6EEB00B395DF /* AnimatedFrame.swift in Sources */,
 				00B8C75F1A364DCE00C188E7 /* ImageSourceHelpers.swift in Sources */,
+				00978B6C1D9C6D2A00A6575F /* Animator.swift in Sources */,
 				007E08441BD95E6200883D0C /* ArrayExtension.swift in Sources */,
 				EAF49C7F1A3A4DE000B395DF /* UIImageExtension.swift in Sources */,
 			);

GifuTests/GifuTests.swift

@@ -6,39 +6,50 @@ private let imageData = testImageDataNamed("mugen.gif")
 private let staticImage = UIImage(data: imageData)!
 private let preloadFrameCount = 20
 
+class DummyAnimatorDelegate: AnimatorDelegate {
+  func animatorHasNewFrame() { }
+}
+
 class GifuTests: XCTestCase {
   var animator: Animator!
   var originalFrameCount: Int!
+  let delegate = DummyAnimatorDelegate()
 
   override func setUp() {
     super.setUp()
-    animator = Animator(data: imageData, size: CGSize.zero, contentMode: .scaleToFill, framePreloadCount: preloadFrameCount)
+    animator = Animator(withDelegate: delegate)
-    originalFrameCount = Int(CGImageSourceGetCount(animator.imageSource))
+    animator.prepareForAnimation(withGIFData: imageData, size: staticImage.size, contentMode: .scaleToFill)
+    originalFrameCount = 44
   }
   
   func testIsAnimatable() {
-    XCTAssertTrue(animator.isAnimatable)
+    XCTAssertNotNil(animator.frameStore)
+    guard let store = animator.frameStore else { return }
+    XCTAssertTrue(store.isAnimatable)
   }
 
   func testCurrentFrame() {
-    XCTAssertEqual(animator.currentFrameIndex, 0)
+    XCTAssertNotNil(animator.frameStore)
-    XCTAssertEqual(animator.currentFrameDuration, TimeInterval.infinity)
+    guard let store = animator.frameStore else { return }
-    XCTAssertNil(animator.currentFrameImage)
+    XCTAssertEqual(store.currentFrameIndex, 0)
   }
 
   func testFramePreload() {
+    XCTAssertNotNil(animator.frameStore)
+    guard let store = animator.frameStore else { return }
+
     let expectation = self.expectation(description: "frameDuration")
 
-    animator.prepareFrames {
+    store.prepareFrames {
-      let animatedFrameCount = self.animator.animatedFrames.count
+      let animatedFrameCount = store.animatedFrames.count
       XCTAssertEqual(animatedFrameCount, self.originalFrameCount)
-      XCTAssertNotNil(self.animator.frame(at: preloadFrameCount - 1))
+      XCTAssertNotNil(store.frame(at: preloadFrameCount - 1))
-      XCTAssertNil(self.animator.frame(at: preloadFrameCount + 1)?.images)
+      XCTAssertNil(store.frame(at: preloadFrameCount + 1)?.images)
-      XCTAssertEqual(self.animator.currentFrameIndex, 0)
+      XCTAssertEqual(store.currentFrameIndex, 0)
 
-      self.animator.shouldChangeFrame(with: 1.0) { hasNewFrame in
+      store.shouldChangeFrame(with: 1.0) { hasNewFrame in
         XCTAssertTrue(hasNewFrame)
-        XCTAssertEqual(self.animator.currentFrameIndex, 1)
+        XCTAssertEqual(store.currentFrameIndex, 1)
         expectation.fulfill()
       }
     }
@@ -51,13 +62,16 @@ class GifuTests: XCTestCase {
   }
 
   func testFrameInfo() {
+    XCTAssertNotNil(animator.frameStore)
+    guard let store = animator.frameStore else { return }
+
     let expectation = self.expectation(description: "testFrameInfoIsAccurate")
 
-    animator.prepareFrames {
+    store.prepareFrames {
-      let frameDuration = self.animator.frame(at: 5)?.duration ?? 0
+      let frameDuration = store.frame(at: 5)?.duration ?? 0
       XCTAssertTrue((frameDuration - 0.05) < 0.00001)
 
-      let imageSize = self.animator.frame(at: 5)?.size ?? CGSize.zero
+      let imageSize = store.frame(at: 5)?.size ?? CGSize.zero
       XCTAssertEqual(imageSize, staticImage.size)
 
       expectation.fulfill()

Source/AnimatableImageView.swift

@@ -1,134 +0,0 @@
-import UIKit
-
-/// A subclass of `UIImageView` that can be animated using an image name string or raw data.
-public class AnimatableImageView: UIImageView {
-  /// Proxy object for preventing a reference cycle between the CADisplayLink and AnimatableImageView.
-  /// Source: http://merowing.info/2015/11/the-beauty-of-imperfection/
-  fileprivate class TargetProxy {
-    private weak var target: AnimatableImageView?
-
-    init(target: AnimatableImageView) {
-      self.target = target
-    }
-
-    @objc func onScreenUpdate() {
-      target?.updateFrameIfNeeded()
-    }
-  }
-
-  /// An `Animator` instance that holds the frames of a specific image in memory.
-  var animator: Animator?
-
-  /// A flag to avoid invalidating the displayLink on deinit if it was never created
-  private var displayLinkInitialized: Bool = false
-
-  /// A display link that keeps calling the `updateFrame` method on every screen refresh.
-  lazy var displayLink: CADisplayLink = { [unowned self] in
-    self.displayLinkInitialized = true
-    let display = CADisplayLink(target: TargetProxy(target: self), selector: #selector(TargetProxy.onScreenUpdate))
-    display.isPaused = true
-    return display
-  }()
-
-  /// The size of the frame cache.
-  public var framePreloadCount = 50
-
-  /// Specifies whether the GIF frames should be pre-scaled to save memory. Default is **false**.
-  public var needsPrescaling = false
-
-  /// A computed property that returns whether the image view is animating.
-  public var isAnimatingGIF: Bool {
-    return !displayLink.isPaused
-  }
-
-  /// A computed property that returns the total number of frames in the GIF.
-  public var frameCount: Int {
-    return animator?.frameCount ?? 0
-  }
-
-  /// Prepares the frames using a GIF image file name, without starting the animation.
-  /// The file name should include the `.gif` extension.
-  ///
-  /// - parameter imageName: The name of the GIF file. The method looks for the file in the app bundle.
-  public func prepareForAnimation(withGIFNamed imageName: String) {
-    guard let extensionRemoved = imageName.components(separatedBy: ".")[safe: 0],
-    let imagePath = Bundle.main.url(forResource: extensionRemoved, withExtension: "gif"),
-      let data = try? Data(contentsOf: imagePath) else { return }
-
-    prepareForAnimation(withGIFData: data)
-  }
-
-  /// Prepares the frames using raw GIF image data, without starting the animation.
-  ///
-  /// - parameter data: GIF image data.
-  public func prepareForAnimation(withGIFData imageData: Data) {
-    image = UIImage(data: imageData)
-    animator = Animator(data: imageData, size: frame.size, contentMode: contentMode, framePreloadCount: framePreloadCount)
-    animator?.needsPrescaling = needsPrescaling
-    animator?.prepareFrames()
-    attachDisplayLink()
-  }
-
-  /// Prepares the frames using a GIF image file name and starts animating the image view.
-  ///
-  /// - parameter imageName: The name of the GIF file. The method looks for the file in the app bundle.
-  public func animate(withGIFNamed imageName: String) {
-    prepareForAnimation(withGIFNamed: imageName)
-    startAnimatingGIF()
-  }
-
-  /// Prepares the frames using raw GIF image data and starts animating the image view.
-  ///
-  /// - parameter data: GIF image data.
-  public func animate(withGIFData data: Data) {
-    prepareForAnimation(withGIFData: data)
-    startAnimatingGIF()
-  }
-
-  /// Updates the `image` property of the image view if necessary. This method should not be called manually.
-  override public func display(_ layer: CALayer) {
-    image = animator?.currentFrameImage ?? image
-  }
-
-  /// Starts the image view animation.
-  public func startAnimatingGIF() {
-    if animator?.isAnimatable ?? false {
-      displayLink.isPaused = false
-    }
-  }
-
-  /// Stops the image view animation.
-  public func stopAnimatingGIF() {
-    displayLink.isPaused = true
-  }
-
-  /// Reset the image view values.
-  public func prepareForReuse() {
-    stopAnimatingGIF()
-    animator = nil
-  }
-
-  /// Update the current frame if needed.
-  func updateFrameIfNeeded() {
-    guard let animator = animator else { return }
-    animator.shouldChangeFrame(with: displayLink.duration) { hasNewFrame in
-      if hasNewFrame { self.layer.setNeedsDisplay() }
-    }
-  }
-
-  /// Invalidate the displayLink so it releases its target.
-  deinit {
-    if displayLinkInitialized {
-      displayLink.invalidate()
-    }
-  }
-
-  /// Attaches the display link.
-  func attachDisplayLink() {
-    displayLink.add(to: .main, forMode: RunLoopMode.commonModes)
-  }
-
-  public override var intrinsicContentSize: CGSize {
-    return image?.size ?? CGSize.zero
-  }
-}

Source/AnimatedFrame.swift

@@ -1,8 +1,10 @@
-/// Keeps a reference to an `UIImage` instance and its duration as a GIF frame.
+/// Represents a single frame in a GIF.
 struct AnimatedFrame {
-  /// The image that should be used for this frame.
+
+  /// The image to display for this frame. Its value is nil when the frame is removed from the buffer.
   let image: UIImage?
-  /// The duration that the frame image should be displayed.
+  
+  /// The duration that this frame should remain active.
   let duration: TimeInterval
 
   /// A placeholder frame with no image assigned.
@@ -11,15 +13,15 @@ struct AnimatedFrame {
     return AnimatedFrame(image: nil, duration: duration)
   }
 
-  /// Whether the AnimatedFrame instance contains an image or not.
+  /// Whether this frame instance contains an image or not.
   var isPlaceholder: Bool {
     return image == .none
   }
 
-  /// Takes an optional image and returns an non-placeholder `AnimatedFrame`.
+  /// Returns a new instance from an ptional image.
   ///
   /// - parameter image: An optional `UIImage` instance to be assigned to the new frame.
-  /// - returns: A non-placeholder `AnimatedFrame` instance.
+  /// - returns: An `AnimatedFrame` instance.
   func animatedFrame(with newImage: UIImage?) -> AnimatedFrame {
     return AnimatedFrame(image: newImage, duration: duration)
   }

Source/Animator.swift

@@ -1,214 +1,154 @@
-import UIKit
-import ImageIO
 
-/// Responsible for storing and updating the frames of a `AnimatableImageView` instance via delegation.
+/// Handles the GIF animation logic.
-class Animator {
+public class Animator {
-  /// Maximum duration to increment the frame timer with.
-  let maxTimeStep = 1.0
-  /// An array of animated frames from a single GIF image.
-  var animatedFrames = [AnimatedFrame]()
-  /// The size to resize all frames to
-  let size: CGSize
-  /// The content mode to use when resizing
-  let contentMode: UIViewContentMode
-  /// Maximum number of frames to load at once
-  let preloadFrameCount: Int
-  /// The total number of frames in the GIF.
-  var frameCount = 0
-  /// A reference to the original image source.
-  var imageSource: CGImageSource
 
-  /// The index of the current GIF frame.
+  /// Number of frame to buffer.
-  var currentFrameIndex = 0 {
+  public var frameBufferCount = 50
-    didSet {
-      previousFrameIndex = oldValue
-    }
-  }
 
-  /// The index of the previous GIF frame.
+  /// Specifies whether GIF frames should be resized.
-  var previousFrameIndex = 0 {
+  public var shouldResizeFrames = false
-    didSet {
+
-      preloadFrameQueue.async {
+  /// Responsible for loading individual frames and resizing them if necessary.
-        self.updatePreloadedFrames()
+  var frameStore: FrameStore?
-      }
+
-    }
+  /// Tracks whether the display link is initialized.
-  }
+  private var displayLinkInitialized: Bool = false
-  /// Time elapsed since the last frame change. Used to determine when the frame should be updated.
+
-  var timeSinceLastFrameChange: TimeInterval = 0.0
+  /// A delegate responsible for displaying the GIF frames.
-  /// Specifies whether GIF frames should be pre-scaled.
+  private weak var delegate: AnimatorDelegate!
-  /// - seealso: `needsPrescaling` in AnimatableImageView.
+
-  var needsPrescaling = true
+  /// Responsible for starting and stopping the animation.
-  /// Dispatch queue used for preloading images.
+  private lazy var displayLink: CADisplayLink = { [unowned self] in
-  private lazy var preloadFrameQueue: DispatchQueue = {
+    self.displayLinkInitialized = true
-    return DispatchQueue(label: "co.kaishin.Gifu.preloadQueue")
+    let display = CADisplayLink(target: DisplayLinkProxy(target: self), selector: #selector(DisplayLinkProxy.onScreenUpdate))
+    display.isPaused = true
+    return display
   }()
-  /// The current image frame to show.
+
-  var currentFrameImage: UIImage? {
+  /// Introspect whether the `displayLink` is paused.
-    return frame(at: currentFrameIndex)
+  var isAnimating: Bool {
+    return !displayLink.isPaused
   }
 
-  /// The current frame duration
+  /// Total frame count of the GIF.
-  var currentFrameDuration: TimeInterval {
+  var frameCount: Int {
-    return duration(at: currentFrameIndex)
+    return frameStore?.frameCount ?? 0
   }
 
-  /// Is this image animatable?
+  /// Instantiates a new animator object with a delegate view.
-  var isAnimatable: Bool {
-    return imageSource.isAnimatedGIF
-  }
-
-  /// Initializes an animator instance from raw GIF image data and an `Animatable` delegate.
   ///
-  /// - parameter data: The raw GIF image data.
+  /// - parameter view: A view object that implements the `GIFAnimatable` protocol.
-  /// - parameter delegate: An `Animatable` delegate.
+  ///
-  init(data: Data, size: CGSize, contentMode: UIViewContentMode, framePreloadCount: Int) {
+  /// - returns: A new animator instance.
-    let options = [String(kCGImageSourceShouldCache): kCFBooleanFalse] as CFDictionary
+  public init(withDelegate delegate: AnimatorDelegate) {
-    self.imageSource = CGImageSourceCreateWithData(data as CFData, options) ?? CGImageSourceCreateIncremental(options)
+    self.delegate = delegate
-    self.size = size
-    self.contentMode = contentMode
-    self.preloadFrameCount = framePreloadCount
   }
 
-  // MARK: - Frames
+  /// Checks if there is a new frame to display.
-  /// Loads the frames from an image source, resizes them, then caches them in `animatedFrames`.
+  fileprivate func updateFrameIfNeeded() {
-  func prepareFrames(_ completionHandler: ((Void) -> Void)? = .none) {
+    guard let store = frameStore else { return }
-    frameCount = Int(CGImageSourceGetCount(imageSource))
+    store.shouldChangeFrame(with: displayLink.duration) {
-    animatedFrames.reserveCapacity(frameCount)
+      if $0 { delegate.animatorHasNewFrame() }
-    preloadFrameQueue.async {
-      self.setupAnimatedFrames()
-      if let handler = completionHandler { handler() }
     }
   }
 
-  /// Returns the frame at a particular index.
+
+  /// Prepares the animator instance for animation.
   ///
-  /// - parameter index: The index of the frame.
+  /// - parameter imageName:   The file name of the GIF in the main bundle.
-  /// - returns: An optional image at a given frame.
+  /// - parameter size:        The target size of the individual frames.
-  func frame(at index: Int) -> UIImage? {
+  /// - parameter contentMode: The view content mode to use for the individual frames.
-    return animatedFrames[safe: index]?.image
+  func prepareForAnimation(withGIFNamed imageName: String, size: CGSize, contentMode: UIViewContentMode) {
+    guard let extensionRemoved = imageName.components(separatedBy: ".")[safe: 0],
+      let imagePath = Bundle.main.url(forResource: extensionRemoved, withExtension: "gif"),
+      let data = try? Data(contentsOf: imagePath) else { return }
+
+    prepareForAnimation(withGIFData: data, size: size, contentMode: contentMode)
   }
 
-  /// Returns the duration at a particular index.
+  /// Prepares the animator instance for animation.
   ///
-  /// - parameter index: The index of the duration.
+  /// - parameter imageData:   GIF image data.
-  /// - returns: The duration of the given frame.
+  /// - parameter size:        The target size of the individual frames.
-  func duration(at index: Int) -> TimeInterval {
+  /// - parameter contentMode: The view content mode to use for the individual frames.
-	return animatedFrames[safe: index]?.duration ?? TimeInterval.infinity
+  func prepareForAnimation(withGIFData imageData: Data, size: CGSize, contentMode: UIViewContentMode) {
+    frameStore = FrameStore(data: imageData, size: size, contentMode: contentMode, framePreloadCount: frameBufferCount)
+    frameStore?.shouldResizeFrames = shouldResizeFrames
+    frameStore?.prepareFrames()
+    attachDisplayLink()
   }
 
-  /// Checks whether the frame should be changed and calls a handler with the results.
-  ///
-  /// - parameter duration: A `CFTimeInterval` value that will be used to determine whether frame should be changed.
-  /// - parameter handler: A function that takes a `Bool` and returns nothing. It will be called with the frame change result.
-  func shouldChangeFrame(with duration: CFTimeInterval, handler: (Bool) -> Void) {
-    incrementTimeSinceLastFrameChange(with: duration)
 
-    if currentFrameDuration > timeSinceLastFrameChange {
+  /// Add the display link to the main run loop.
-      handler(false)
+  private func attachDisplayLink() {
-    } else {
+    displayLink.add(to: .main, forMode: RunLoopMode.commonModes)
-      resetTimeSinceLastFrameChange()
+  }
-      incrementCurrentFrameIndex()
+
-      handler(true)
+  deinit {
+    if displayLinkInitialized {
+      displayLink.invalidate()
     }
   }
+
+  /// Start animating.
+  func startAnimating() {
+    if frameStore?.isAnimatable ?? false {
+      displayLink.isPaused = false
+    }
+  }
+
+  /// Stop animating.
+  func stopAnimating() {
+    displayLink.isPaused = true
+  }
+
+  /// Prepare for animation and start animating immediately.
+  ///
+  /// - parameter imageName:   The file name of the GIF in the main bundle.
+  /// - parameter size:        The target size of the individual frames.
+  /// - parameter contentMode: The view content mode to use for the individual frames.
+  func animate(withGIFNamed imageName: String, size: CGSize, contentMode: UIViewContentMode) {
+    prepareForAnimation(withGIFNamed: imageName, size: size, contentMode: contentMode)
+    startAnimating()
+  }
+
+  /// Prepare for animation and start animating immediately.
+  ///
+  /// - parameter imageData:   GIF image data.
+  /// - parameter size:        The target size of the individual frames.
+  /// - parameter contentMode: The view content mode to use for the individual frames.
+  func animate(withGIFData data: Data, size: CGSize, contentMode: UIViewContentMode) {
+    prepareForAnimation(withGIFData: data, size: size, contentMode: contentMode)
+    startAnimating()
+  }
+
+  /// Stop animating and nullify the frame store.
+  func prepareForReuse() {
+    stopAnimating()
+    frameStore = nil
+  }
+
+  /// Gets the current image from the frame store.
+  ///
+  /// - returns: An optional frame image to display.
+  public func imageToDisplay() -> UIImage? {
+    return frameStore?.currentFrameImage
+  }
 }
 
-private extension Animator {
+/// A proxy class to avoid a retain cycyle with the display link.
-  /// Whether preloading is needed or not.
+fileprivate class DisplayLinkProxy {
-  var preloadingIsNeeded: Bool {
-    return preloadFrameCount < frameCount - 1
-  }
 
-  /// Optionally loads a single frame from an image source, resizes it if requierd, then returns an `UIImage`.
+  /// The target animator.
+  private weak var target: Animator?
+
+  /// Init with target animator.
   ///
-  /// - parameter index: The index of the frame to load.
+  /// - parameter target: An animator instance.
-  /// - returns: An optional `UIImage` instance.
-  func loadFrame(at index: Int) -> UIImage? {
-    guard let imageRef = CGImageSourceCreateImageAtIndex(imageSource, index, nil) else { return .none }
-    let image = UIImage(cgImage: imageRef)
-    let scaledImage: UIImage?
-
-    if needsPrescaling {
-      switch self.contentMode {
-      case .scaleAspectFit: scaledImage = image.constrained(by: size)
-      case .scaleAspectFill: scaledImage = image.filling(size: size)
-      default: scaledImage = image.resized(to: size)
-      }
-    } else {
-      scaledImage = image
-    }
-
-    return scaledImage
-  }
-
-  /// Updates the frames by preloading new ones and replacing the previous frame with a placeholder.
-  func updatePreloadedFrames() {
-    if !preloadingIsNeeded { return }
-    animatedFrames[previousFrameIndex] = animatedFrames[previousFrameIndex].placeholderFrame
-
-    preloadIndexes(withStartingIndex: currentFrameIndex).forEach { index in
-      let currentAnimatedFrame = animatedFrames[index]
-      if !currentAnimatedFrame.isPlaceholder { return }
-      animatedFrames[index] = currentAnimatedFrame.animatedFrame(with: loadFrame(at: index))
-    }
-  }
-
-  /// Increments the `timeSinceLastFrameChange` property with a given duration.
   ///
-  /// - parameter duration: An `NSTimeInterval` value to increment the `timeSinceLastFrameChange` property with.
+  /// - returns: A new proxy instance.
-  func incrementTimeSinceLastFrameChange(with duration: TimeInterval) {
+  init(target: Animator) { self.target = target }
-    timeSinceLastFrameChange += min(maxTimeStep, duration)
-  }
 
-  /// Ensures that `timeSinceLastFrameChange` remains accurate after each frame change by substracting the `currentFrameDuration`.
+  /// Lets the target update the frame if needed.
-  func resetTimeSinceLastFrameChange() {
+  @objc func onScreenUpdate() { target?.updateFrameIfNeeded() }
-    timeSinceLastFrameChange -= currentFrameDuration
-  }
-
-  /// Increments the `currentFrameIndex` property.
-  func incrementCurrentFrameIndex() {
-    currentFrameIndex = increment(index: currentFrameIndex)
-  }
-
-  /// Increments a given frame index, taking into account the `frameCount` and looping when necessary.
-  ///
-  /// - parameter index: The `Int` value to increment.
-  /// - parameter byValue: The `Int` value to increment with.
-  /// - returns: A new `Int` value.
-  func increment(index: Int, by value: Int = 1) -> Int {
-    return (index + value) % frameCount
-  }
-
-  /// Returns the indexes of the frames to preload based on a starting frame index.
-  ///
-  /// - parameter index: Starting index.
-  /// - returns: An array of indexes to preload.
-  func preloadIndexes(withStartingIndex index: Int) -> [Int] {
-    let nextIndex = increment(index: index)
-    let lastIndex = increment(index: index, by: preloadFrameCount)
-
-    if lastIndex >= nextIndex {
-      return [Int](nextIndex...lastIndex)
-    } else {
-      return [Int](nextIndex..<frameCount) + [Int](0...lastIndex)
-    }
-  }
-
-  /// Set up animated frames after resetting them if necessary.
-  func setupAnimatedFrames() {
-    resetAnimatedFrames()
-
-    (0..<frameCount).forEach { index in
-      let frameDuration = CGImageFrameDuration(with: imageSource, atIndex: index)
-      animatedFrames += [AnimatedFrame(image: .none, duration: frameDuration)]
-
-      if index > preloadFrameCount { return }
-      animatedFrames[index] = animatedFrames[index].animatedFrame(with: loadFrame(at: index))
-    }
-  }
-
-  /// Reset animated frames.
-  func resetAnimatedFrames() {
-    animatedFrames = []
-  }
 }

Source/AnimatorDelegate.swift

@@ -0,0 +1,4 @@
+/// The protocol that an animator delegate needs to conform to.
+public protocol AnimatorDelegate: class {
+  func animatorHasNewFrame()
+}

Source/FrameStore.swift

@@ -0,0 +1,224 @@
+import UIKit
+import ImageIO
+
+/// Responsible for storing and updating the frames of a single GIF.
+class FrameStore {
+
+  /// Maximum duration to increment the frame timer with.
+  let maxTimeStep = 1.0
+
+  /// An array of animated frames from a single GIF image.
+  var animatedFrames = [AnimatedFrame]()
+
+  /// The target size for all frames.
+  let size: CGSize
+
+  /// The content mode to use when resizing.
+  let contentMode: UIViewContentMode
+
+  /// Maximum number of frames to load at once
+  let bufferFrameCount: Int
+
+  /// The total number of frames in the GIF.
+  var frameCount = 0
+
+  /// A reference to the original image source.
+  var imageSource: CGImageSource
+
+  /// The index of the current GIF frame.
+  var currentFrameIndex = 0 {
+    didSet {
+      previousFrameIndex = oldValue
+    }
+  }
+
+  /// The index of the previous GIF frame.
+  var previousFrameIndex = 0 {
+    didSet {
+      preloadFrameQueue.async {
+        self.updatePreloadedFrames()
+      }
+    }
+  }
+
+  /// Time elapsed since the last frame change. Used to determine when the frame should be updated.
+  var timeSinceLastFrameChange: TimeInterval = 0.0
+
+  /// Specifies whether GIF frames should be resized.
+  var shouldResizeFrames = true
+  
+  /// Dispatch queue used for preloading images.
+  private lazy var preloadFrameQueue: DispatchQueue = {
+    return DispatchQueue(label: "co.kaishin.Gifu.preloadQueue")
+  }()
+
+  /// The current image frame to show.
+  var currentFrameImage: UIImage? {
+    return frame(at: currentFrameIndex)
+  }
+
+  /// The current frame duration
+  var currentFrameDuration: TimeInterval {
+    return duration(at: currentFrameIndex)
+  }
+
+  /// Is this image animatable?
+  var isAnimatable: Bool {
+    return imageSource.isAnimatedGIF
+  }
+
+  /// Initializes an animator instance from raw GIF image data and an `Animatable` delegate.
+  ///
+  /// - parameter data: The raw GIF image data.
+  /// - parameter delegate: An `Animatable` delegate.
+  init(data: Data, size: CGSize, contentMode: UIViewContentMode, framePreloadCount: Int) {
+    let options = [String(kCGImageSourceShouldCache): kCFBooleanFalse] as CFDictionary
+    self.imageSource = CGImageSourceCreateWithData(data as CFData, options) ?? CGImageSourceCreateIncremental(options)
+    self.size = size
+    self.contentMode = contentMode
+    self.bufferFrameCount = framePreloadCount
+  }
+
+  // MARK: - Frames
+  /// Loads the frames from an image source, resizes them, then caches them in `animatedFrames`.
+  func prepareFrames(_ completionHandler: ((Void) -> Void)? = .none) {
+    frameCount = Int(CGImageSourceGetCount(imageSource))
+    animatedFrames.reserveCapacity(frameCount)
+    preloadFrameQueue.async {
+      self.setupAnimatedFrames()
+      if let handler = completionHandler { handler() }
+    }
+  }
+
+  /// Returns the frame at a particular index.
+  ///
+  /// - parameter index: The index of the frame.
+  /// - returns: An optional image at a given frame.
+  func frame(at index: Int) -> UIImage? {
+    return animatedFrames[safe: index]?.image
+  }
+
+  /// Returns the duration at a particular index.
+  ///
+  /// - parameter index: The index of the duration.
+  /// - returns: The duration of the given frame.
+  func duration(at index: Int) -> TimeInterval {
+	return animatedFrames[safe: index]?.duration ?? TimeInterval.infinity
+  }
+
+  /// Checks whether the frame should be changed and calls a handler with the results.
+  ///
+  /// - parameter duration: A `CFTimeInterval` value that will be used to determine whether frame should be changed.
+  /// - parameter handler: A function that takes a `Bool` and returns nothing. It will be called with the frame change result.
+  func shouldChangeFrame(with duration: CFTimeInterval, handler: (Bool) -> Void) {
+    incrementTimeSinceLastFrameChange(with: duration)
+
+    if currentFrameDuration > timeSinceLastFrameChange {
+      handler(false)
+    } else {
+      resetTimeSinceLastFrameChange()
+      incrementCurrentFrameIndex()
+      handler(true)
+    }
+  }
+}
+
+private extension FrameStore {
+  /// Whether preloading is needed or not.
+  var preloadingIsNeeded: Bool {
+    return bufferFrameCount < frameCount - 1
+  }
+
+  /// Optionally loads a single frame from an image source, resizes it if required, then returns an `UIImage`.
+  ///
+  /// - parameter index: The index of the frame to load.
+  /// - returns: An optional `UIImage` instance.
+  func loadFrame(at index: Int) -> UIImage? {
+    guard let imageRef = CGImageSourceCreateImageAtIndex(imageSource, index, nil) else { return .none }
+    let image = UIImage(cgImage: imageRef)
+    let scaledImage: UIImage?
+
+    if shouldResizeFrames {
+      switch self.contentMode {
+      case .scaleAspectFit: scaledImage = image.constrained(by: size)
+      case .scaleAspectFill: scaledImage = image.filling(size: size)
+      default: scaledImage = image.resized(to: size)
+      }
+    } else {
+      scaledImage = image
+    }
+
+    return scaledImage
+  }
+
+  /// Updates the frames by preloading new ones and replacing the previous frame with a placeholder.
+  func updatePreloadedFrames() {
+    if !preloadingIsNeeded { return }
+    animatedFrames[previousFrameIndex] = animatedFrames[previousFrameIndex].placeholderFrame
+
+    preloadIndexes(withStartingIndex: currentFrameIndex).forEach { index in
+      let currentAnimatedFrame = animatedFrames[index]
+      if !currentAnimatedFrame.isPlaceholder { return }
+      animatedFrames[index] = currentAnimatedFrame.animatedFrame(with: loadFrame(at: index))
+    }
+  }
+
+  /// Increments the `timeSinceLastFrameChange` property with a given duration.
+  ///
+  /// - parameter duration: An `NSTimeInterval` value to increment the `timeSinceLastFrameChange` property with.
+  func incrementTimeSinceLastFrameChange(with duration: TimeInterval) {
+    timeSinceLastFrameChange += min(maxTimeStep, duration)
+  }
+
+  /// Ensures that `timeSinceLastFrameChange` remains accurate after each frame change by substracting the `currentFrameDuration`.
+  func resetTimeSinceLastFrameChange() {
+    timeSinceLastFrameChange -= currentFrameDuration
+  }
+
+  /// Increments the `currentFrameIndex` property.
+  func incrementCurrentFrameIndex() {
+    currentFrameIndex = increment(index: currentFrameIndex)
+  }
+
+  /// Increments a given frame index, taking into account the `frameCount` and looping when necessary.
+  ///
+  /// - parameter index: The `Int` value to increment.
+  /// - parameter byValue: The `Int` value to increment with.
+  /// - returns: A new `Int` value.
+  func increment(index: Int, by value: Int = 1) -> Int {
+    return (index + value) % frameCount
+  }
+
+  /// Returns the indexes of the frames to preload based on a starting frame index.
+  ///
+  /// - parameter index: Starting index.
+  /// - returns: An array of indexes to preload.
+  func preloadIndexes(withStartingIndex index: Int) -> [Int] {
+    let nextIndex = increment(index: index)
+    let lastIndex = increment(index: index, by: bufferFrameCount)
+
+    if lastIndex >= nextIndex {
+      return [Int](nextIndex...lastIndex)
+    } else {
+      return [Int](nextIndex..<frameCount) + [Int](0...lastIndex)
+    }
+  }
+
+  /// Set up animated frames after resetting them if necessary.
+  func setupAnimatedFrames() {
+    resetAnimatedFrames()
+
+    (0..<frameCount).forEach { index in
+      let frameDuration = CGImageFrameDuration(with: imageSource, atIndex: index)
+      animatedFrames += [AnimatedFrame(image: .none, duration: frameDuration)]
+
+      if index > bufferFrameCount { return }
+      animatedFrames[index] = animatedFrames[index].animatedFrame(with: loadFrame(at: index))
+    }
+  }
+
+  /// Reset animated frames.
+  func resetAnimatedFrames() {
+    animatedFrames = []
+  }
+}

Source/GIFAnimatable.swift

@@ -0,0 +1,91 @@
+/// The protocol that view classes need to conform to to enable animated GIF support.
+public protocol GIFAnimatable: class, AnimatorDelegate, CALayerDelegate {
+
+  /// Responsible for managing the animation frames.
+  var animator: Animator? { get set }
+
+  /// Used for displaying the animation frames.
+  var image: UIImage? { get set }
+
+  /// Notifies the instance that it needs display.
+  var layer: CALayer { get }
+
+  /// View frame used for resizing the frames.
+  var frame: CGRect { get set }
+
+  /// Content mode used for resizing the frames.
+  var contentMode: UIViewContentMode { get set }
+
+  /// Implement this method and call `updateImageIfNeeded` from within it in your conforming class.
+  ///
+  /// - parameter layer:
+  func display(_ layer: CALayer)
+
+  /// Needs to be called whenever the conforming class needs to check if it needs to update the current frame being displayed.
+  func updateImageIfNeeded()
+}
+extension GIFAnimatable {
+  /// Returns the intrinsic content size based on the size of the image.
+  public var intrinsicContentSize: CGSize {
+    return image?.size ?? CGSize.zero
+  }
+
+  /// Prepare for animation and start animating immediately.
+  ///
+  /// - parameter imageName:   The file name of the GIF in the main bundle.
+  public func animate(withGIFNamed imageName: String) {
+    animator?.animate(withGIFNamed: imageName, size: frame.size, contentMode: contentMode)
+  }
+
+  /// Introspect whether the instance is animating.
+  public var isAnimatingGIF: Bool {
+    return animator?.isAnimating ?? false
+  }
+
+  /// Prepares the animator instance for animation.
+  ///
+  /// - parameter imageName:   The file name of the GIF in the main bundle.
+  public func prepareForAnimation(withGIFNamed imageName: String) {
+    animator?.prepareForAnimation(withGIFNamed: imageName, size: frame.size, contentMode: contentMode)
+  }
+
+  /// Prepare for animation and start animating immediately.
+  ///
+  /// - parameter imageData:   GIF image data.
+  public func prepareForAnimation(withGIFData imageData: Data) {
+    image = UIImage(data: imageData)
+    animator?.prepareForAnimation(withGIFData: imageData, size: frame.size, contentMode: contentMode)
+  }
+
+  /// Total frame count of the GIF.
+  public var frameCount: Int {
+    return animator?.frameCount ?? 0
+  }
+
+  /// Stop animating and free up GIF data from memory.
+  public func prepareForReuse() {
+    animator?.prepareForReuse()
+  }
+
+  /// Start animating GIF.
+  public func startAnimatingGIF() {
+    animator?.startAnimating()
+  }
+
+  /// Stop animating GIF.
+  public func stopAnimatingGIF() {
+    animator?.stopAnimating()
+  }
+
+  /// Updates the image with a new frame if necessary.
+  public func updateImageIfNeeded() {
+    image = animator?.imageToDisplay() ?? image
+  }
+}
+
+extension GIFAnimatable {
+  /// Calls setNeedsDisplay on the layer whenever the animator has a new frame. Should *not* be called directly.
+  public func animatorHasNewFrame() {
+    layer.setNeedsDisplay()
+  }
+}

Source/GIFImageView.swift

@@ -0,0 +1,16 @@
+import UIKit
+
+
+/// Example class that conforms to `GIFAnimatable`. Uses default values for the animator frame buffer count and resize behavior.
+public class GIFImageView: UIImageView, GIFAnimatable {
+  public var animator: Animator?
+
+  required public init?(coder aDecoder: NSCoder) {
+    super.init(coder: aDecoder)
+    animator = Animator(withDelegate: self)
+  }
+
+  override public func display(_ layer: CALayer) {
+    updateImageIfNeeded()
+  }
+}

Source/Info.plist

@@ -19,7 +19,7 @@
 	<key>CFBundleSignature</key>
 	<string>????</string>
 	<key>CFBundleVersion</key>
-	<string>102</string>
+	<string>118</string>
 	<key>NSPrincipalClass</key>
 	<string></string>
 </dict>