insidegui · May 13, 2022 21:27 · May 13, 2022
diff --git a/FixSwiftUIMaterialInPreviews.m b/FixSwiftUIMaterialInPreviews.m
@@ -0,0 +1,44 @@
+#if DEBUG
+
+/*
+This fixes SwiftUI previews not rendering translucent materials correctly by
+swizzling a couple of properties on NSWindow.
+
+Just drop into your project and add to the target being previewed (or something it links against).
+
+Notice the #if DEBUG, so this code won't end up in release builds. It also checks for the 
+XCODE_RUNNING_FOR_PREVIEWS environment variable so that it won't affect regular debug builds of the app.
+*/
+
+@import ObjectiveC.runtime;
+
+@interface FixSwiftUIMaterialInPreviews : NSObject
+
+@end
+
+@implementation FixSwiftUIMaterialInPreviews
+
++ (void)load
+{
+    NSDictionary *env = [NSProcessInfo processInfo].environment;
+    BOOL isSwiftUIPreview = [env[@"XCODE_RUNNING_FOR_PREVIEWS"] boolValue];
+    if (!isSwiftUIPreview) return;
+
+    NSLog(@"😇 Installing fix for translucency in SwiftUI previews");
+
+    Method hasKeyAppearance = class_getInstanceMethod([NSWindow class], NSSelectorFromString(@"hasKeyAppearance"));
+    Method hasMainAppearance = class_getInstanceMethod([NSWindow class], NSSelectorFromString(@"hasMainAppearance"));
+    Method override = class_getClassMethod([self class], @selector(__hasKeyAppearanceOverride));
+
+    if (hasKeyAppearance) method_exchangeImplementations(hasKeyAppearance, override);
+    if (hasMainAppearance) method_exchangeImplementations(hasMainAppearance, override);
+}
+
++ (BOOL)__hasKeyAppearanceOverride
+{
+    return YES;
+}
+
+@end
+
+#endif