Fix the issue that WebImage's onSuccess does not get called when memory cache hit for new created View Struct

Author: dreampiggy

SDWebImageSwiftUI/Classes/ImageManager.swift

@@ -19,6 +19,7 @@ class ImageManager : ObservableObject {
     weak var currentOperation: SDWebImageOperation? = nil
     var isSuccess: Bool = false // true means request for this URL is ended forever, load() do nothing
     var isIncremental: Bool = false // true means during incremental loading
+    var isFirstLoad: Bool = true // false after first call `load()`
 
     var url: URL?
     var options: SDWebImageOptions
@@ -39,6 +40,7 @@ class ImageManager : ObservableObject {
     }
 
     func load() {
+        isFirstLoad = false
         if currentOperation != nil {
             return
         }

SDWebImageSwiftUI/Classes/WebImage.swift

@@ -58,13 +58,16 @@ public struct WebImage : View {
             }
         }
         self.imageManager = ImageManager(url: url, options: options, context: context)
-        // load remote image here, SwiftUI sometimes will create a new View struct without calling `onAppear` (like enter EditMode) :)
-        // this can ensure we load the image, SDWebImage take care of the duplicated query
-        self.imageManager.load()
     }
 
     public var body: some View {
-        Group {
+        // 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 {
             if imageManager.image != nil {
                 if isAnimating && !self.imageManager.isIncremental {
                     if currentFrame != nil {