Add support for using a spring generator as a timing curve.

examples/apps/Catalog/MotionAnimatorCatalog.xcodeproj/project.pbxproj

@@ -25,6 +25,7 @@
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+		668819F81FE2E5C6003A9420 /* SpringTimingCurveTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 668819F71FE2E5C6003A9420 /* SpringTimingCurveTests.swift */; };
 		669B6CA91FD0547100B80B76 /* MotionAnimatorBehavioralTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 669B6CA81FD0547100B80B76 /* MotionAnimatorBehavioralTests.swift */; };
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@@ -80,6 +81,7 @@
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+		668819F71FE2E5C6003A9420 /* SpringTimingCurveTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = SpringTimingCurveTests.swift; sourceTree = "<group>"; };
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@@ -241,6 +243,7 @@
 				669B6CA81FD0547100B80B76 /* MotionAnimatorBehavioralTests.swift */,
 				66FD99F91EE9FBBE00C53A82 /* MotionAnimatorTests.m */,
 				668726491EF04B4C00113675 /* MotionAnimatorTests.swift */,
+				668819F71FE2E5C6003A9420 /* SpringTimingCurveTests.swift */,
 				664F59991FCE6661002EC56D /* NonAdditiveAnimatorTests.swift */,
 				664F59951FCDB2E5002EC56D /* QuartzCoreBehavioralTests.swift */,
 				660636011FACC24300C3DFB8 /* TimeScaleFactorTests.swift */,
@@ -522,6 +525,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				668819F81FE2E5C6003A9420 /* SpringTimingCurveTests.swift in Sources */,
 				6625876C1FB4DB9C00BC7DF1 /* InitialVelocityTests.swift in Sources */,
 				66EF6F281FC33C4800C83A63 /* HeadlessLayerImplicitAnimationTests.swift in Sources */,
 				664F599A1FCE6661002EC56D /* NonAdditiveAnimatorTests.swift in Sources */,

src/private/CABasicAnimation+MotionAnimator.m

@@ -81,20 +81,29 @@ static BOOL IsAnimationKeyPathAlwaysNonAdditive(NSString *keyPath) {
     return animation;
   }
 
-  if ([traits.timingCurve isKindOfClass:[MDMSpringTimingCurve class]]) {
-    MDMSpringTimingCurve *springTiming = (MDMSpringTimingCurve *)traits.timingCurve;
-
+  CABasicAnimation *(^animationFromSpring)(MDMSpringTimingCurve *) =
+      ^(MDMSpringTimingCurve *springTiming) {
 #pragma clang diagnostic push
-    // CASpringAnimation is a private API on iOS 8 - we're able to make use of it because we're
-    // linking against the public API on iOS 9+.
+        // CASpringAnimation is a private API on iOS 8 - we're able to make use of it because we're
+        // linking against the public API on iOS 9+.
 #pragma clang diagnostic ignored "-Wpartial-availability"
-    CASpringAnimation *animation = [CASpringAnimation animation];
+        CASpringAnimation *animation = [CASpringAnimation animation];
 #pragma clang diagnostic pop
-    animation.mass = springTiming.mass;
-    animation.stiffness = springTiming.tension;
-    animation.damping = springTiming.friction;
-    animation.duration = traits.duration;
-    return animation;
+        animation.mass = springTiming.mass;
+        animation.stiffness = springTiming.tension;
+        animation.damping = springTiming.friction;
+        animation.duration = traits.duration;
+        return animation;
+      };
+
+  if ([traits.timingCurve isKindOfClass:[MDMSpringTimingCurveGenerator class]]) {
+    MDMSpringTimingCurveGenerator *springTimingGenerator =
+        (MDMSpringTimingCurveGenerator *)traits.timingCurve;
+    return animationFromSpring(springTimingGenerator.springTimingCurve);
+  }
+
+  if ([traits.timingCurve isKindOfClass:[MDMSpringTimingCurve class]]) {
+    return animationFromSpring((MDMSpringTimingCurve *)traits.timingCurve);
   }
 
   return nil;

tests/unit/SpringTimingCurveTests.swift

@@ -0,0 +1,76 @@
+/*
+ Copyright 2017-present The Material Motion Authors. All Rights Reserved.
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+
+import XCTest
+#if IS_BAZEL_BUILD
+import _MotionAnimator
+#else
+import MotionAnimator
+#endif
+
+class SpringTimingCurveTests: XCTestCase {
+  var animator: MotionAnimator!
+  var traits: MDMAnimationTraits!
+  var view: UIView!
+
+  var originalImplementation: IMP?
+  override func setUp() {
+    super.setUp()
+
+    animator = MotionAnimator()
+    traits = MDMAnimationTraits(duration: 1)
+
+    let window = UIWindow()
+    window.makeKeyAndVisible()
+    view = UIView() // Need to animate a view's layer to get implicit animations.
+    window.addSubview(view)
+
+    // Connect our layers to the render server.
+    CATransaction.flush()
+  }
+
+  override func tearDown() {
+    animator = nil
+    traits = nil
+    view = nil
+
+    super.tearDown()
+  }
+
+  @available(iOS 9.0, *)
+  func testGeneratorCanBeUsedAsATimingCurve() {
+    traits.timingCurve = MDMSpringTimingCurveGenerator(duration: traits.duration, dampingRatio: 0.5)
+
+    animator.animate(with: traits, between: [1, 0], layer: view.layer, keyPath: .cornerRadius)
+
+    XCTAssertNotNil(view.layer.animationKeys(),
+                    "Expected an animation to be added, but none were found.")
+    guard let animationKeys = view.layer.animationKeys() else {
+      return
+    }
+    XCTAssertEqual(animationKeys.count, 1,
+                   "Expected only one animation to be added, but the following were found: "
+                    + "\(animationKeys).")
+    guard let key = animationKeys.first else {
+      return
+    }
+    XCTAssertTrue(view.layer.animation(forKey: key) is CASpringAnimation,
+                  "Expected the animation to be a spring, but it was not: "
+                  + " \(view.layer.animation(forKey: key).debugDescription)")
+
+  }
+
+}