Fix a potential crash (#30)

DarkModeKit.xcodeproj/project.pbxproj

@@ -18,6 +18,8 @@
 		8CAFD9E723716054001A63B8 /* DarkModeKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 8C1915CE2361EFDB004A606A /* DarkModeKit.framework */; };
 		8CAFD9E823716054001A63B8 /* DarkModeKit.framework in Embed Frameworks */ = {isa = PBXBuildFile; fileRef = 8C1915CE2361EFDB004A606A /* DarkModeKit.framework */; settings = {ATTRIBUTES = (CodeSignOnCopy, RemoveHeadersOnCopy, ); }; };
 		8CAFD9ED2371606D001A63B8 /* NavigationController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8CAFD9EC2371606D001A63B8 /* NavigationController.swift */; };
+		8CB63E41238551F3008ABCE2 /* UIView+DarkModeKit.h in Headers */ = {isa = PBXBuildFile; fileRef = 8CB63E3F238551F3008ABCE2 /* UIView+DarkModeKit.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		8CB63E42238551F3008ABCE2 /* UIView+DarkModeKit.m in Sources */ = {isa = PBXBuildFile; fileRef = 8CB63E40238551F3008ABCE2 /* UIView+DarkModeKit.m */; };
 		8CDA628C2366DAA9004895B5 /* DarkModeKit.h in Headers */ = {isa = PBXBuildFile; fileRef = 8CDA62702366DAA9004895B5 /* DarkModeKit.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		8CDA628D2366DAA9004895B5 /* DMTraitCollection.h in Headers */ = {isa = PBXBuildFile; fileRef = 8CDA62712366DAA9004895B5 /* DMTraitCollection.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		8CDA628E2366DAA9004895B5 /* DMTraitCollection.m in Sources */ = {isa = PBXBuildFile; fileRef = 8CDA62722366DAA9004895B5 /* DMTraitCollection.m */; };
@@ -91,6 +93,8 @@
 		8CAFD9E023715FAB001A63B8 /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.storyboard; name = Base; path = Base.lproj/LaunchScreen.storyboard; sourceTree = "<group>"; };
 		8CAFD9E223715FAB001A63B8 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		8CAFD9EC2371606D001A63B8 /* NavigationController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NavigationController.swift; sourceTree = "<group>"; };
+		8CB63E3F238551F3008ABCE2 /* UIView+DarkModeKit.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "UIView+DarkModeKit.h"; sourceTree = "<group>"; };
+		8CB63E40238551F3008ABCE2 /* UIView+DarkModeKit.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = "UIView+DarkModeKit.m"; sourceTree = "<group>"; };
 		8CDA62702366DAA9004895B5 /* DarkModeKit.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = DarkModeKit.h; sourceTree = "<group>"; };
 		8CDA62712366DAA9004895B5 /* DMTraitCollection.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = DMTraitCollection.h; sourceTree = "<group>"; };
 		8CDA62722366DAA9004895B5 /* DMTraitCollection.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = DMTraitCollection.m; sourceTree = "<group>"; };
@@ -175,6 +179,8 @@
 				8CDA62722366DAA9004895B5 /* DMTraitCollection.m */,
 				8C071AEA23683BF5001AB7B2 /* NSObject+DarkModeKit.h */,
 				8C071AEB23683BF5001AB7B2 /* NSObject+DarkModeKit.m */,
+				8CB63E3F238551F3008ABCE2 /* UIView+DarkModeKit.h */,
+				8CB63E40238551F3008ABCE2 /* UIView+DarkModeKit.m */,
 			);
 			path = DarkModeCore;
 			sourceTree = "<group>";
@@ -272,6 +278,7 @@
 				8C071AEC23683BF5001AB7B2 /* NSObject+DarkModeKit.h in Headers */,
 				8CDA628D2366DAA9004895B5 /* DMTraitCollection.h in Headers */,
 				8CDA628C2366DAA9004895B5 /* DarkModeKit.h in Headers */,
+				8CB63E41238551F3008ABCE2 /* UIView+DarkModeKit.h in Headers */,
 				8CDA62912366DAA9004895B5 /* DMDynamicImage.h in Headers */,
 				8CDA62A52366DAA9004895B5 /* DMDynamicColor.h in Headers */,
 			);
@@ -409,6 +416,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				8CDA62972366DAA9004895B5 /* UIScrollView+Theme.swift in Sources */,
+				8CB63E42238551F3008ABCE2 /* UIView+DarkModeKit.m in Sources */,
 				8CDA62A12366DAA9004895B5 /* UITextField+Theme.swift in Sources */,
 				8CDA62952366DAA9004895B5 /* UIWindow+Theme.swift in Sources */,
 				8CDA629E2366DAA9004895B5 /* UIViewController+Theme.swift in Sources */,

Sources/DarkModeCore/DarkModeKit.h

@@ -7,6 +7,7 @@
 #import <DarkModeKit/DMDynamicImage.h>
 #import <DarkModeKit/DMTraitCollection.h>
 #import <DarkModeKit/NSObject+DarkModeKit.h>
+#import <DarkModeKit/UIView+DarkModeKit.h>
 
 //! Project version number for DarkModeKit.
 FOUNDATION_EXPORT double DarkModeKitVersionNumber;

Sources/DarkModeCore/UIView+DarkModeKit.h

@@ -0,0 +1,20 @@
+//
+//  Copyright (c) Microsoft Corporation. All rights reserved.
+//  Licensed under the MIT License.
+//
+
+#import <UIKit/UIKit.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class DMDynamicColor;
+
+@interface UIView (DarkModeKit)
+
++ (void)dm_swizzleSetBackgroundColor;
+
+@property (nonatomic, copy, nullable) DMDynamicColor *dm_dynamicBackgroundColor;
+
+@end
+
+NS_ASSUME_NONNULL_END

Sources/DarkModeCore/UIView+DarkModeKit.m

@@ -0,0 +1,45 @@
+//
+//  Copyright (c) Microsoft Corporation. All rights reserved.
+//  Licensed under the MIT License.
+//
+
+#import "UIView+DarkModeKit.h"
+#import "DMDynamicColor.h"
+
+@import ObjectiveC;
+
+@implementation UIView (DarkModeKit)
+
+static void (*dm_original_setBackgroundColor)(UIView *, SEL, UIColor *);
+
+static void dm_setBackgroundColor(UIView *self, SEL _cmd, UIColor *color) {
+  if ([color isKindOfClass:[DMDynamicColor class]]) {
+    self.dm_dynamicBackgroundColor = (DMDynamicColor *)color;
+  } else {
+    self.dm_dynamicBackgroundColor = nil;
+  }
+  dm_original_setBackgroundColor(self, _cmd, color);
+}
+
+// https://stackoverflow.com/questions/42677534/swizzling-on-properties-that-conform-to-ui-appearance-selector
++ (void)dm_swizzleSetBackgroundColor {
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    Method method = class_getInstanceMethod(self, @selector(setBackgroundColor:));
+    dm_original_setBackgroundColor = (void *)method_getImplementation(method);
+    method_setImplementation(method, (IMP)dm_setBackgroundColor);
+  });
+}
+
+- (DMDynamicColor *)dm_dynamicBackgroundColor {
+  return objc_getAssociatedObject(self, _cmd);
+}
+
+- (void)setDm_dynamicBackgroundColor:(DMDynamicColor *)dm_dynamicBackgroundColor {
+  objc_setAssociatedObject(self,
+                           @selector(dm_dynamicBackgroundColor),
+                           dm_dynamicBackgroundColor,
+                           OBJC_ASSOCIATION_COPY_NONATOMIC);
+}
+
+@end

Sources/DarkModeKit/DarkModeManager.swift

@@ -38,7 +38,7 @@ public final class DarkModeManager: NSObject {
 
     // Colors
     UIView.swizzleWillMoveToWindowOnce
-    UIView.swizzleSetBackgroundColorOnce
+    UIView.dm_swizzleSetBackgroundColor()
     UIView.swizzleSetTintColorOnce
     UITextField.swizzleTextFieldWillMoveToWindowOnce
     UILabel.swizzleDidMoveToWindowOnce

Sources/DarkModeKit/ThemeableExtensions/UIView+Theme.swift

@@ -17,7 +17,7 @@ extension UIView: Themeable {
   }
 
   @objc func _updateDynamicColors() {
-    if let dynamicBackgroundColor = _dynamicBackgroundColor {
+    if let dynamicBackgroundColor = dm_dynamicBackgroundColor {
       backgroundColor = dynamicBackgroundColor
     }
     if let dynamicTintColor = _dynamicTintColor {
@@ -48,37 +48,20 @@ extension UIView {
 
 extension UIView {
   private struct Constants {
-    static var dynamicBackgroundColorKey = "dynamicBackgroundColorKey"
     static var dynamicTintColorKey = "dynamicTintColorKey"
   }
 
-  static let swizzleSetBackgroundColorOnce: Void = {
-    if !dm_swizzleInstanceMethod(#selector(setter: backgroundColor), to: #selector(outlookSetBackgroundColor)) {
-      assertionFailure(DarkModeManager.messageForSwizzlingFailed(class: UIView.self, selector: #selector(setter: backgroundColor)))
-    }
-  }()
-
   static let swizzleSetTintColorOnce: Void = {
     if !dm_swizzleInstanceMethod(#selector(setter: tintColor), to: #selector(outlookSetTintColor)) {
       assertionFailure(DarkModeManager.messageForSwizzlingFailed(class: UIView.self, selector: #selector(setter: tintColor)))
     }
   }()
 
-  private var _dynamicBackgroundColor: DynamicColor? {
-    get { return objc_getAssociatedObject(self, &Constants.dynamicBackgroundColorKey) as? DynamicColor }
-    set { objc_setAssociatedObject(self, &Constants.dynamicBackgroundColorKey, newValue, .OBJC_ASSOCIATION_COPY_NONATOMIC) }
-  }
-
   private var _dynamicTintColor: DynamicColor? {
     get { return objc_getAssociatedObject(self, &Constants.dynamicTintColorKey) as? DynamicColor }
     set { objc_setAssociatedObject(self, &Constants.dynamicTintColorKey, newValue, .OBJC_ASSOCIATION_COPY_NONATOMIC) }
   }
 
-  @objc private dynamic func outlookSetBackgroundColor(_ color: UIColor) {
-    _dynamicBackgroundColor = color as? DynamicColor
-    outlookSetBackgroundColor(color)
-  }
-
   @objc private dynamic func outlookSetTintColor(_ color: UIColor) {
     _dynamicTintColor = color as? DynamicColor
     outlookSetTintColor(color)

Tests/DarkModeKitTests/DarkModeKitTests.swift

@@ -6,4 +6,10 @@
 import XCTest
 @testable import DarkModeKit
 
-final class DarkModeKitTests: XCTestCase {}
+final class DarkModeKitTests: XCTestCase {
+  func testSetBackgroundColorSwizzling() {
+    UIWindow.appearance().backgroundColor = .white
+    DarkModeManager.setup(updateAppearance: { _ in })
+    _ = UIWindow()
+  }
+}