From dabc94ceb3279b336ea1acb77f0301d51a681380 Mon Sep 17 00:00:00 2001
From: Maciej Swic <maciej@swic.name>
Date: Fri, 13 Aug 2021 21:00:52 +0200
Subject: [PATCH] Use PreferenceKeys to pass images up the view hieararchy.

---
 Sources/ImageViewer/ImageViewerSupport.swift | 71 ++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 Sources/ImageViewer/ImageViewerSupport.swift

diff --git a/Sources/ImageViewer/ImageViewerSupport.swift b/Sources/ImageViewer/ImageViewerSupport.swift
new file mode 100644
index 0000000..f9d5864
--- /dev/null
+++ b/Sources/ImageViewer/ImageViewerSupport.swift
@@ -0,0 +1,71 @@
+//
+//  ImageViewerSupport.swift
+//  ImageViewerSupport
+//
+//  Created by Maciej Świć on 2021-08-13.
+//
+
+import SwiftUI
+import ImageViewer
+
+extension View {
+    /// Attaches an image viewer to this view using a PreferenceKey.
+    ///
+    /// Allows this view to display images as requested by child views further down in the view hierarchy, without having to manually pass the image throught the view hierarchy.
+    ///
+    /// For example, you can attach this modifier to a `NavigationView` and use the `viewImage(image: UIImage?)`modifier on any view further down in the hierarchy.
+    public func imageViewier() -> some View {
+        self.modifier(ImageViewerViewModifier())
+    }
+    
+    /// Sets the image to be viewed with the `imageViewer()` modifer.
+    ///
+    /// Use this on the child view to specify which image should be viewed higher up in the hierarchy.
+    ///
+    /// For example, you can use this modifier on a `Button` in a `List` several hierarchies down where you don't have access to a `NavigationView`.
+    ///
+    /// Then, you can use the `imageViewer()` modifier anywhere higher up in that hierarchy, for example on a `NavigationView` to display the image properly.
+    public func viewImage(image: UIImage?) -> some View {
+        self.modifier(ImageViewerSetModifier(image: image))
+    }
+}
+
+struct ImageViewerViewModifier: ViewModifier {
+    @State var isShowingImage = false
+    @State var imagePreference: Image? {
+        didSet {
+            isShowingImage = imagePreference != nil
+        }
+    }
+    
+    func body(content: Content) -> some View {
+        content
+            .onPreferenceChange(ImageViewPreferenceKey.self) { image in
+                guard let image = image else { return }
+                
+                imagePreference = Image(uiImage: image)
+            }
+            .overlay {
+                ImageViewer(image: $imagePreference, viewerShown: $isShowingImage)
+            }
+    }
+}
+
+struct ImageViewerSetModifier: ViewModifier {
+    var image: UIImage?
+    
+    func body(content: Content) -> some View {
+        content
+            .preference(key: ImageViewPreferenceKey.self, value: image)
+    }
+}
+
+struct ImageViewPreferenceKey: PreferenceKey {
+    static var defaultValue: UIImage?
+    
+    static func reduce(value: inout UIImage?, nextValue: () -> UIImage?) {
+        guard let nextValue = nextValue() else { return }
+        
+        value = nextValue
+    }
+}