Merge pull request #47 from SDWebImage/feature_convenient_placeholder_webimage

Add the convenient method for WebImage to directly supply SwiftUI.Image for placeholder

Author: dreampiggy

README.md

@@ -90,8 +90,10 @@ var body: some View {
             // Success
         }
         .resizable() // Resizable like SwiftUI.Image
+        .placeholder(Image(systemName: "photo")) // Placeholder Image
+        // Supports ViewBuilder as well
         .placeholder {
-            Image(systemName: "photo") // Placeholder
+            Rectangle().foregroundColor(.gray)
         }
         .indicator(.activity) // Activity Indicator
         .animation(.easeInOut(duration: 0.5)) // Animation Duration
@@ -121,7 +123,7 @@ var body: some View {
             // Error
         }
         .resizable() // Actually this is not needed unlike SwiftUI.Image
-        .placeholder(UIImage(systemName: "photo")) // Placeholder
+        .placeholder(UIImage(systemName: "photo")) // Placeholder Image
         .indicator(SDWebImageActivityIndicator.medium) // Activity Indicator
         .transition(.fade) // Fade Transition
         .scaledToFit() // Attention to call it on AnimatedImage, but not `some View` after View Modifier
@@ -155,7 +157,7 @@ If you don't need animated image, prefer to use `WebImage` firstly. Which behave
 
 If you need animated image, `AnimatedImage` is the one to choose. Remember it supports static image as well, you don't need to check the format, just use as it.
 
-But, because `AnimatedImage` use `UIViewRepresentable` and driven by UIKit, currently there may be some small incompatible issues between UIKit and SwiftUI layout and animation system. We try our best to match SwiftUI behavior, and provide the same API as `WebImage`, which make it easy to switch between these two types.
+But, because `AnimatedImage` use `UIViewRepresentable` and driven by UIKit, currently there may be some small incompatible issues between UIKit and SwiftUI layout and animation system, or bugs related to SwiftUI itself. We try our best to match SwiftUI behavior, and provide the same API as `WebImage`, which make it easy to switch between these two types if needed.
 
 For more information, it's really recommended to check our demo below, to learn detailed API usage.
 

SDWebImageSwiftUI/Classes/WebImage.swift

@@ -151,6 +151,17 @@ extension WebImage {
         return result
     }
 
+    /// Associate a placeholder image when loading image with url
+    /// - note: This placeholder image will apply the same size and resizable from WebImage for convenience. If you don't want this, use the ViewBuilder one above instead
+    /// - Parameter image: A Image view that describes the placeholder.
+    public func placeholder(_ image: Image) -> WebImage {
+        return placeholder {
+            configurations.reduce(image) { (previous, configuration) in
+                configuration(previous)
+            }
+        }
+    }
+    
     /// Control the behavior to retry the failed loading when view become appears again
     /// - Parameter flag: Whether or not to retry the failed loading
     public func retryOnAppear(_ flag: Bool) -> WebImage {