From d9fd4726eaf1a8816c765986de8b9d5d111e65f9 Mon Sep 17 00:00:00 2001
From: DreamPiggy <lizhuoli1126@126.com>
Date: Tue, 31 Mar 2020 17:24:47 +0800
Subject: [PATCH] Using a more trick but smart solution for cases when WebImage
 is used during transition state, like scaleEffect. In this time, we does not
 trigger a actualy image loading, only query the memory cache for quickly
 placeholder

---
 Example/SDWebImageSwiftUIDemo/DetailView.swift |  8 ++++----
 SDWebImageSwiftUI/Classes/ImageManager.swift   | 17 +++++++++++++++++
 SDWebImageSwiftUI/Classes/WebImage.swift       | 16 +++++++++-------
 3 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/Example/SDWebImageSwiftUIDemo/DetailView.swift b/Example/SDWebImageSwiftUIDemo/DetailView.swift
index eacbbd2..f3cf15c 100644
--- a/Example/SDWebImageSwiftUIDemo/DetailView.swift
+++ b/Example/SDWebImageSwiftUIDemo/DetailView.swift
@@ -38,7 +38,7 @@ struct DetailView: View {
     let url: String
     let animated: Bool
     @State var isAnimating: Bool = true
-    @State var lastScaleValue: CGFloat = 1.0
+    @State var lastScale: CGFloat = 1.0
     @State var scale: CGFloat = 1.0
     @Environment(\.presentationMode) var presentationMode
     @EnvironmentObject var settings: UserSettings
@@ -75,12 +75,12 @@ struct DetailView: View {
         return contentView()
             .scaleEffect(self.scale)
             .gesture(MagnificationGesture(minimumScaleDelta: 0.1).onChanged { value in
-                let delta = value / self.lastScaleValue
-                self.lastScaleValue = value
+                let delta = value / self.lastScale
+                self.lastScale = value
                 let newScale = self.scale * delta
                 self.scale = min(max(newScale, 0.5), 2)
             }.onEnded { value in
-                self.lastScaleValue = 1.0
+                self.lastScale = 1.0
             })
         #endif
         #if os(tvOS)
diff --git a/SDWebImageSwiftUI/Classes/ImageManager.swift b/SDWebImageSwiftUI/Classes/ImageManager.swift
index 7726769..a148a2e 100644
--- a/SDWebImageSwiftUI/Classes/ImageManager.swift
+++ b/SDWebImageSwiftUI/Classes/ImageManager.swift
@@ -106,6 +106,23 @@ public final class ImageManager : ObservableObject {
         }
     }
     
+    /// Prefetch the initial state of image
+    internal func prefetch() {
+        let key = manager.cacheKey(for: url)
+        if let imageCache = manager.imageCache as? SDImageCache {
+            self.image = imageCache.imageFromMemoryCache(forKey: key)
+        } else {
+            // generic API
+            manager.imageCache.containsImage(forKey: key, cacheType: .memory) { [unowned self] (cacheType) in
+                if cacheType == .memory {
+                    self.manager.imageCache.queryImage(forKey: key, options: self.options, context: self.context) { [unowned self] (image, data, cacheType) in
+                        self.image = image
+                    }
+                }
+            }
+        }
+    }
+    
 }
 
 // Completion Handler
diff --git a/SDWebImageSwiftUI/Classes/WebImage.swift b/SDWebImageSwiftUI/Classes/WebImage.swift
index 424552d..bbb04ae 100644
--- a/SDWebImageSwiftUI/Classes/WebImage.swift
+++ b/SDWebImageSwiftUI/Classes/WebImage.swift
@@ -57,16 +57,13 @@ public struct WebImage : View {
             }
         }
         self.imageManager = ImageManager(url: url, options: options, context: context)
+        // this prefetch the memory cache of image, to immediately render it on screen
+        // this solve the cause when `onAppear` not been called, for example, some transaction indetermite state :)
+        self.imageManager.prefetch()
     }
     
     public var body: some View {
-        // load remote image when first called `body`, SwiftUI sometimes will create a new View struct without calling `onAppear` (like enter EditMode) :)
-        // this can ensure we load the image, and display image synchronously when memory cache hit to avoid flashing
-        // called once per struct, SDWebImage take care of the duplicated query
-        if imageManager.isFirstLoad {
-            imageManager.load()
-        }
-        return Group {
+        Group {
             if imageManager.image != nil {
                 if isAnimating && !self.imageManager.isIncremental {
                     if currentFrame != nil {
@@ -109,6 +106,11 @@ public struct WebImage : View {
                 setupPlaceholder()
                 .frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: .infinity)
                 .onAppear {
+                    // load remote image when first appear
+                    if self.imageManager.isFirstLoad {
+                        self.imageManager.load()
+                        return
+                    }
                     guard self.retryOnAppear else { return }
                     // When using prorgessive loading, the new partial image will cause onAppear. Filter this case
                     if self.imageManager.image == nil && !self.imageManager.isIncremental {