Add support for dynamic placeholder images (#613)

Before this change, if you attempted to use a dynamic image for a placeholder
(e.g. an image from an asset catalog that has both dark and light versions)
you would get unpredictable results. This is because PINAnimatedImageView
is drawing the image directly to the layer without consulting the view's
current trait collection. So which version of the image you get depends
entirely on what the global `UITraitCollection.currentTraitCollection` is.

According to Apple, "UIKit updates the value of this property before calling
several well-known methods of UIView, UIViewController, and UIPresentationController."
Though they do not say what those methods are, experimentation concludes
that "displayLayer:" is not one of those.

To solve this, we need to make sure that when we generate the CGImage,
we are explicit about using the view's trait collection so that we
get the correct image.

Author: bdolman

PINRemoteImage.xcodeproj/project.pbxproj

@@ -109,6 +109,8 @@
 		A7343C5B228993D100972894 /* NSHTTPURLResponse+MaxAge.m in Sources */ = {isa = PBXBuildFile; fileRef = ACD28EAE81695DDF84BB76B8 /* NSHTTPURLResponse+MaxAge.m */; };
 		A7343C60228993F400972894 /* NSHTTPURLResponse+MaxAge.m in Sources */ = {isa = PBXBuildFile; fileRef = ACD28EAE81695DDF84BB76B8 /* NSHTTPURLResponse+MaxAge.m */; };
 		ACD28AB87FABF6BA3B9BF4E4 /* NSDate+PINCacheTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ACD28D963D79EEC14EE071CE /* NSDate+PINCacheTests.m */; };
+		B5BB4023274DB69F0042AE1D /* Media.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = B5BB4022274DB69F0042AE1D /* Media.xcassets */; };
+		B5BB4024274DB69F0042AE1D /* Media.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = B5BB4022274DB69F0042AE1D /* Media.xcassets */; };
 		D93A340224182D46005EB15E /* TestAnimatedImage.m in Sources */ = {isa = PBXBuildFile; fileRef = D93A340124182D46005EB15E /* TestAnimatedImage.m */; };
 		D93A340324182D46005EB15E /* TestAnimatedImage.m in Sources */ = {isa = PBXBuildFile; fileRef = D93A340124182D46005EB15E /* TestAnimatedImage.m */; };
 		F1B918FF1BCF23C900710963 /* PINRemoteImageCategoryManager.m in Sources */ = {isa = PBXBuildFile; fileRef = F1B918DC1BCF23C800710963 /* PINRemoteImageCategoryManager.m */; };
@@ -268,6 +270,7 @@
 		ACD28A0374E664CFF0BB3297 /* NSHTTPURLResponse+MaxAge.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "NSHTTPURLResponse+MaxAge.h"; sourceTree = "<group>"; };
 		ACD28D963D79EEC14EE071CE /* NSDate+PINCacheTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "NSDate+PINCacheTests.m"; sourceTree = "<group>"; };
 		ACD28EAE81695DDF84BB76B8 /* NSHTTPURLResponse+MaxAge.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "NSHTTPURLResponse+MaxAge.m"; sourceTree = "<group>"; };
+		B5BB4022274DB69F0042AE1D /* Media.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; path = Media.xcassets; sourceTree = "<group>"; };
 		D93A340024182D46005EB15E /* TestAnimatedImage.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = TestAnimatedImage.h; sourceTree = "<group>"; };
 		D93A340124182D46005EB15E /* TestAnimatedImage.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = TestAnimatedImage.m; sourceTree = "<group>"; };
 		F1B918D11BCF239200710963 /* PINRemoteImage.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = PINRemoteImage.framework; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -381,6 +384,7 @@
 				683128F41F95045200D5B4A8 /* PINAnimatedImage+PINAnimatedImageTesting.m */,
 				ACD288C6E6B13E6DA226D252 /* NSDate+PINCacheTests.h */,
 				ACD28D963D79EEC14EE071CE /* NSDate+PINCacheTests.m */,
+				B5BB4022274DB69F0042AE1D /* Media.xcassets */,
 			);
 			path = Tests;
 			sourceTree = "<group>";
@@ -803,13 +807,15 @@
 			isa = PBXResourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				B5BB4024274DB69F0042AE1D /* Media.xcassets in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
 		68A0FC171E523434000B552D /* Resources */ = {
 			isa = PBXResourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				B5BB4023274DB69F0042AE1D /* Media.xcassets in Resources */,
 				0E71BE2A22E94C7200FC5B99 /* fireworks.gif in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;

Source/Classes/AnimatedImages/PINAnimatedImageView.m

@@ -271,6 +271,13 @@ - (CGImageRef)imageRef
     if (_animatedImage) {
         return _frameImage;
     } else if ((underlyingImage = [super image])) {
+#if PIN_TARGET_IOS
+        if (@available(iOS 13.0, tvOS 10.0, *)) {
+            if (underlyingImage.imageAsset != nil) {
+                underlyingImage = [underlyingImage.imageAsset imageWithTraitCollection:self.traitCollection];
+            }
+        }
+#endif
         return (CGImageRef)CFAutorelease(CFRetain([underlyingImage CGImage]));
     }
     return nil;

Tests/Media.xcassets/Contents.json

@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

Tests/Media.xcassets/DynamicImage.imageset/Contents.json

@@ -0,0 +1,22 @@
+{
+  "images" : [
+    {
+      "filename" : "Light.png",
+      "idiom" : "universal"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "filename" : "Dark.png",
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

Tests/Media.xcassets/DynamicImage.imageset/Dark.png

@@ -260,4 +260,30 @@ class PINAnimatedImageTests: XCTestCase, PINRemoteImageManagerAlternateRepresent
         index = gifAnimatedImageView.frameIndex(atPlayHeadPosition: 0.41)
         XCTAssert(index == 4)
     }
+    
+    @available(iOS 13.0, tvOS 10.0, *)
+    func testDynamicPlaceholderImages() {
+        let bundle = Bundle(for: type(of: self))
+        let dynamicImage = UIImage(named: "DynamicImage", in: bundle, with: nil)
+        XCTAssertNotNil(dynamicImage, "Unable to read image")
+        
+        let lightTraitCollection = UITraitCollection(traitsFrom: [.current, .init(userInterfaceStyle: .light)])
+        let darkTraitCollection = UITraitCollection(traitsFrom: [.current, .init(userInterfaceStyle: .dark)])
+        
+        let lightImage = dynamicImage?.imageAsset?.image(with: lightTraitCollection).cgImage
+        let darkImage = dynamicImage?.imageAsset?.image(with: darkTraitCollection).cgImage
+        
+        let imageView = PINAnimatedImageView()
+        imageView.image = dynamicImage
+        
+        let layer = CALayer()
+        
+        imageView.overrideUserInterfaceStyle = .light
+        imageView.display(layer)
+        XCTAssert(lightImage === (layer.contents as! CGImage), "Placeholder image should be using light mode version")
+        
+        imageView.overrideUserInterfaceStyle = .dark
+        imageView.display(layer)
+        XCTAssert(darkImage === (layer.contents as! CGImage), "Placeholder image should be using dark mode version")
+    }
 }