Fix borked frame preloading

Demo/demo/Images.xcassets/earth.dataset/Contents.json

@@ -0,0 +1,12 @@
+{
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  },
+  "data" : [
+    {
+      "idiom" : "universal",
+      "filename" : "earth.gif"
+    }
+  ]
+}

Demo/demo/Main.storyboard

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="8191" systemVersion="14F27" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" initialViewController="vXZ-lx-hvc">
+<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="10116" systemVersion="15E65" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" initialViewController="vXZ-lx-hvc">
     <dependencies>
         <deployment identifier="iOS"/>
-        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="8154"/>
+        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="10085"/>
     </dependencies>
     <scenes>
         <!--Gifu-->

GifuTests/GifuTests.swift

@@ -3,58 +3,70 @@ import ImageIO
 @testable import Gifu
 
 private let imageData = testImageDataNamed("mugen.gif")
-private let staticImage = UIImage(data: imageData!)
+private let staticImage = UIImage(data: imageData)!
+private let preloadFrameCount = 20
 
 class GifuTests: XCTestCase {
-  var animator: Animator?
-  var originalFrameCount: Int?
-  var preloadedFrameCount: Int?
+  var animator: Animator!
+  var originalFrameCount: Int!
 
   override func setUp() {
     super.setUp()
-    animator = Animator(data: imageData!, size: CGSizeZero, contentMode: .ScaleToFill, framePreloadCount: 20)
-    animator!.prepareFrames()
-    originalFrameCount = Int(CGImageSourceGetCount(animator!.imageSource))
-    preloadedFrameCount = animator!.animatedFrames.count
-  }
-
-  override func tearDown() {
-    super.tearDown()
+    animator = Animator(data: imageData, size: CGSizeZero, contentMode: .ScaleToFill, framePreloadCount: preloadFrameCount)
+    originalFrameCount = Int(CGImageSourceGetCount(animator.imageSource))
   }
 
   func testIsAnimatable() {
-    XCTAssertTrue(animator!.isAnimatable)
+    XCTAssertTrue(animator.isAnimatable)
   }
 
   func testFramePreload() {
-    XCTAssertLessThanOrEqual(preloadedFrameCount!, originalFrameCount!)
-  }
+    let expectation = expectationWithDescription("frameDuration")
 
-  func testFrameAtIndex() {
-    XCTAssertNotNil(animator!.frameAtIndex(preloadedFrameCount! - 1))
-  }
+    animator.prepareFrames {
+      let animatedFrameCount = self.animator.animatedFrames.count
+      XCTAssertEqual(animatedFrameCount, self.originalFrameCount)
+      XCTAssertNotNil(self.animator.frameAtIndex(preloadFrameCount - 1))
+      XCTAssertNil(self.animator.frameAtIndex(preloadFrameCount + 1)?.images)
+      XCTAssertEqual(self.animator.currentFrameIndex, 0)
 
-  func testFrameDurationPrecision() {
-    let image = animator!.frameAtIndex(5)
-    XCTAssertTrue((image!.duration - 0.05) < 0.00001)
-  }
+      self.animator.shouldChangeFrame(1.0) { hasNewFrame in
+        XCTAssertTrue(hasNewFrame)
+        XCTAssertEqual(self.animator.currentFrameIndex, 1)
+        expectation.fulfill()
+      }
+    }
 
-  func testFrameSize() {
-    let image = animator!.frameAtIndex(5)
-    XCTAssertEqual(image!.size, staticImage!.size)
+    waitForExpectationsWithTimeout(1.0) { error in
+      if let error = error {
+        print("Error: \(error.localizedDescription)")
+      }
+    }
   }
 
-  func testPrepareFramesPerformance() {
-    let tempAnimator = Animator(data: imageData!, size: CGSizeZero, contentMode: .ScaleToFill, framePreloadCount: 50)
+  func testFrameInfo() {
+    let expectation = expectationWithDescription("testFrameInfoIsAccurate")
+
+    animator.prepareFrames {
+      let frameDuration = self.animator.frameAtIndex(5)?.duration ?? 0
+      XCTAssertTrue((frameDuration - 0.05) < 0.00001)
+
+      let imageSize = self.animator.frameAtIndex(5)?.size ?? CGSizeZero
+      XCTAssertEqual(imageSize, staticImage.size)
+
+      expectation.fulfill()
+    }
 
-    self.measureBlock() {
-      tempAnimator.prepareFrames()
+    waitForExpectationsWithTimeout(1.0) { error in
+      if let error = error {
+        print("Error: \(error.localizedDescription)")
+      }
     }
   }
 }
 
-private func testImageDataNamed(name: String) -> NSData? {
+private func testImageDataNamed(name: String) -> NSData {
   let testBundle = NSBundle(forClass: GifuTests.self)
   let imagePath = testBundle.bundleURL.URLByAppendingPathComponent(name)
-  return NSData(contentsOfURL: imagePath)
+  return NSData(contentsOfURL: imagePath)!
 }

Source/AnimatableImageView.swift

@@ -12,7 +12,7 @@ public class AnimatableImageView: UIImageView {
     }
 
     @objc func onScreenUpdate() {
-      target?.updateFrame()
+      target?.updateFrameIfNeeded()
     }
   }
 
@@ -85,7 +85,7 @@ public class AnimatableImageView: UIImageView {
 
   /// Updates the `image` property of the image view if necessary. This method should not be called manually.
   override public func displayLayer(layer: CALayer) {
-    image = animator?.currentFrame
+    image = animator?.currentFrameImage ?? image
   }
 
   /// Starts the image view animation.
@@ -100,16 +100,17 @@ public class AnimatableImageView: UIImageView {
     displayLink.paused = true
   }
 
-  /// Reset the image view values
+  /// Reset the image view values.
   public func prepareForReuse() {
     stopAnimatingGIF()
     animator = nil
   }
 
-  /// Update the current frame with the displayLink duration
-  func updateFrame() {
-    if animator?.updateCurrentFrame(displayLink.duration) ?? false {
-      layer.setNeedsDisplay()
+  /// Update the current frame if needed.
+  func updateFrameIfNeeded() {
+    guard let animator = animator else { return }
+    animator.shouldChangeFrame(displayLink.duration) { hasNewFrame in
+      if hasNewFrame { self.layer.setNeedsDisplay() }
     }
   }
 

Source/AnimatedFrame.swift

@@ -1,10 +1,27 @@
 /// Keeps a reference to an `UIImage` instance and its duration as a GIF frame.
 struct AnimatedFrame {
+  /// The image that should be used for this frame.
   let image: UIImage?
+  /// The duration that the frame image should be displayed.
   let duration: NSTimeInterval
 
-  static func null() -> AnimatedFrame {
-    return AnimatedFrame(image: .None, duration: 0)
+  /// A placeholder frame with no image assigned.
+  /// Used to replace frames that are no longer needed in the animation.
+  var placeholderFrame: AnimatedFrame {
+    return AnimatedFrame(image: nil, duration: duration)
+  }
+
+  /// Whether the AnimatedFrame instance contains an image or not.
+  var isPlaceholder: Bool {
+    return image == .None
+  }
+
+  /// Takes an optional image and returns an non-placeholder `AnimatedFrame`.
+  ///
+  /// - parameter image: An optional `UIImage` instance to be assigned to the new frame.
+  /// - returns: A non-placeholder `AnimatedFrame` instance.
+  func frameWithImage(image: UIImage?) -> AnimatedFrame {
+    return AnimatedFrame(image: image, duration: duration)
   }
 }