Refactors save state thumbnail loading to prevent placeholder image flickering

Common/Components/LoadImageOperation.swift

@@ -9,12 +9,30 @@
 import Foundation
 import ImageIO
 
-public class LoadImageOperation: NSOperation
+import Roxas
+
+public class LoadImageOperation: RSTOperation
 {
     public let URL: NSURL
     
-    public var completionHandler: (UIImage? -> Void)?
+    public var completionHandler: (UIImage? -> Void)? {
-    public var imageCache: NSCache?
+        didSet {
+            self.completionBlock = {
+                rst_dispatch_sync_on_main_thread() {
+                    self.completionHandler?(self.image)
+                }
+            }
+        }
+    }
+    
+    public var imageCache: NSCache? {
+        didSet {
+            // Ensures if an image is cached, it will be returned immediately, to prevent temporary flash of placeholder image
+            self.immediate = self.imageCache?.objectForKey(self.URL) != nil
+        }
+    }
+    
+    private var image: UIImage?
     
     public init(URL: NSURL)
     {
@@ -28,23 +46,11 @@ public extension LoadImageOperation
 {
     override func main()
     {
-        var image: UIImage?
-        
-        defer
-        {
-            if !self.cancelled
-            {
-                dispatch_async(dispatch_get_main_queue()) {
-                    self.completionHandler?(image)
-                }
-            }
-        }
-        
         guard !self.cancelled else { return }
         
         if let cachedImage = self.imageCache?.objectForKey(self.URL) as? UIImage
         {
-            image = cachedImage
+            self.image = cachedImage
             return
         }
         
@@ -61,7 +67,7 @@ public extension LoadImageOperation
             
             self.imageCache?.setObject(loadedImage, forKey: self.URL)
             
-            image = loadedImage
+            self.image = loadedImage
         }
     }
 }

Common/Extensions/NSOperationQueue+KeyValue.swift

@@ -1,41 +0,0 @@
-//
-//  NSOperationQueue+KeyValue.swift
-//  Delta
-//
-//  Created by Riley Testut on 2/26/16.
-//  Copyright © 2016 Riley Testut. All rights reserved.
-//
-
-import Foundation
-import ObjectiveC.runtime
-
-
-extension NSOperationQueue
-{
-    private struct AssociatedKeys
-    {
-        static var OperationsDictionary = "delta_operationsDictionary"
-    }
-
-    private var operationsDictionary: NSMapTable {
-        get {
-            return objc_getAssociatedObject(self, &AssociatedKeys.OperationsDictionary) as? NSMapTable ?? NSMapTable.strongToWeakObjectsMapTable()
-        }
-
-        set {
-            objc_setAssociatedObject(self, &AssociatedKeys.OperationsDictionary, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
-        }
-    }
-    
-    func addOperation(operation: NSOperation, forKey key: AnyObject)
-    {
-        self.operationsDictionary.objectForKey(key)
-        self.addOperation(operation)
-    }
-    
-    func operationForKey(key: AnyObject) -> NSOperation?
-    {
-        let operation = self.operationsDictionary.objectForKey(key) as? NSOperation
-        return operation
-    }
-}

Delta.xcodeproj/project.pbxproj

@@ -10,7 +10,6 @@
 		AF0535CD7331785FA15E0864 /* Pods.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 22506DA00971C4300AF90A35 /* Pods.framework */; };
 		BF090CF41B490D8300DCAB45 /* UIDevice+Vibration.m in Sources */ = {isa = PBXBuildFile; fileRef = BF090CF31B490D8300DCAB45 /* UIDevice+Vibration.m */; };
 		BF0CDDAD1C8155D200640168 /* LoadImageOperation.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF0CDDAC1C8155D200640168 /* LoadImageOperation.swift */; };
-		BF0CDDAF1C81604100640168 /* NSOperationQueue+KeyValue.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF0CDDAE1C81604100640168 /* NSOperationQueue+KeyValue.swift */; };
 		BF107EC41BF413F000E0C32C /* GamesViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF107EC31BF413F000E0C32C /* GamesViewController.swift */; };
 		BF172AEB1C68986300C26774 /* NSManagedObjectContext+Conveniences.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF172AEA1C68986300C26774 /* NSManagedObjectContext+Conveniences.swift */; };
 		BF172AEC1C68986300C26774 /* NSManagedObjectContext+Conveniences.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF172AEA1C68986300C26774 /* NSManagedObjectContext+Conveniences.swift */; };
@@ -135,7 +134,6 @@
 		BF090CF21B490D8300DCAB45 /* UIDevice+Vibration.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "UIDevice+Vibration.h"; sourceTree = "<group>"; };
 		BF090CF31B490D8300DCAB45 /* UIDevice+Vibration.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "UIDevice+Vibration.m"; sourceTree = "<group>"; };
 		BF0CDDAC1C8155D200640168 /* LoadImageOperation.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = LoadImageOperation.swift; path = Components/LoadImageOperation.swift; sourceTree = "<group>"; };
-		BF0CDDAE1C81604100640168 /* NSOperationQueue+KeyValue.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSOperationQueue+KeyValue.swift"; sourceTree = "<group>"; };
 		BF107EC31BF413F000E0C32C /* GamesViewController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = GamesViewController.swift; sourceTree = "<group>"; };
 		BF172AEA1C68986300C26774 /* NSManagedObjectContext+Conveniences.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "NSManagedObjectContext+Conveniences.swift"; sourceTree = "<group>"; };
 		BF1FB1821C5EE643007E2494 /* SaveState+CoreDataProperties.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "SaveState+CoreDataProperties.swift"; sourceTree = "<group>"; };
@@ -318,7 +316,6 @@
 			children = (
 				BF762EAA1BC1B076002C8866 /* NSManagedObject+Conveniences.swift */,
 				BF172AEA1C68986300C26774 /* NSManagedObjectContext+Conveniences.swift */,
-				BF0CDDAE1C81604100640168 /* NSOperationQueue+KeyValue.swift */,
 			);
 			path = Extensions;
 			sourceTree = "<group>";
@@ -723,7 +720,6 @@
 				BF1FB1861C5EE643007E2494 /* SaveState.swift in Sources */,
 				BFB141181BE46934004FBF46 /* GameCollectionViewDataSource.swift in Sources */,
 				BF1FB1841C5EE643007E2494 /* SaveState+CoreDataProperties.swift in Sources */,
-				BF0CDDAF1C81604100640168 /* NSOperationQueue+KeyValue.swift in Sources */,
 				BFFB709F1AF99B1700DE56FE /* EmulationViewController.swift in Sources */,
 				BFAA1FF41B8AD7F900495943 /* ControllersSettingsViewController.swift in Sources */,
 				BF353FF91C5D870B00C1184C /* PauseItem.swift in Sources */,

Delta.xcodeproj/xcshareddata/xcschemes/Delta.xcscheme

@@ -0,0 +1,97 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "0710"
+   version = "1.3">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "BFFA71D61AAC406100EE9DD1"
+               BuildableName = "Delta.app"
+               BlueprintName = "Delta"
+               ReferencedContainer = "container:Delta.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES">
+      <Testables>
+      </Testables>
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "BFFA71D61AAC406100EE9DD1"
+            BuildableName = "Delta.app"
+            BlueprintName = "Delta"
+            ReferencedContainer = "container:Delta.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+      <AdditionalOptions>
+      </AdditionalOptions>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "BFFA71D61AAC406100EE9DD1"
+            BuildableName = "Delta.app"
+            BlueprintName = "Delta"
+            ReferencedContainer = "container:Delta.xcodeproj">
+         </BuildableReference>
+      </BuildableProductRunnable>
+      <CommandLineArguments>
+         <CommandLineArgument
+            argument = "-com.apple.CoreData.ConcurrencyDebug 1"
+            isEnabled = "YES">
+         </CommandLineArgument>
+      </CommandLineArguments>
+      <AdditionalOptions>
+      </AdditionalOptions>
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "BFFA71D61AAC406100EE9DD1"
+            BuildableName = "Delta.app"
+            BlueprintName = "Delta"
+            ReferencedContainer = "container:Delta.xcodeproj">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

Delta/Pause Menu/Save States/SaveStatesViewController.swift

@@ -45,7 +45,7 @@ class SaveStatesViewController: UICollectionViewController
     
     private var fetchedResultsController: NSFetchedResultsController!
     
-    private let imageOperationQueue = NSOperationQueue()
+    private let imageOperationQueue = RSTOperationQueue()
     private let imageCache = NSCache()
     
     private let dateFormatter: NSDateFormatter
@@ -122,7 +122,7 @@ extension SaveStatesViewController
         
         super.viewWillAppear(animated)
     }
-    
+
     override func didReceiveMemoryWarning()
     {
         super.didReceiveMemoryWarning()
@@ -157,26 +157,36 @@ private extension SaveStatesViewController
             self.backgroundView.hidden = false
         }
     }
-}
+    
-
+    //MARK: - Configure Cell -
-private extension SaveStatesViewController
+    
-{
+    func configureCollectionViewCell(cell: GridCollectionViewCell, forIndexPath indexPath: NSIndexPath, ignoreExpensiveOperations ignoreOperations: Bool = false)
-    func configureCollectionViewCell(cell: GridCollectionViewCell, forIndexPath indexPath: NSIndexPath)
     {
         let saveState = self.fetchedResultsController.objectAtIndexPath(indexPath) as! SaveState
         
         cell.imageView.backgroundColor = UIColor.whiteColor()
         cell.imageView.image = UIImage(named: "DeltaPlaceholder")
         
-        let imageOperation = LoadImageOperation(URL: saveState.imageFileURL)
+        if !ignoreOperations
-        imageOperation.completionHandler = { image in
+        {
-            if let image = image
+            let imageOperation = LoadImageOperation(URL: saveState.imageFileURL)
-            {
+            imageOperation.imageCache = self.imageCache
-                cell.imageView.image = image
+            imageOperation.completionHandler = { image in
+                
+                if let image = image
+                {
+                    cell.imageView.image = image
+                }
             }
-        }
+            
-        
+            // Ensure initially visible cells have loaded their image before they appear to prevent potential flickering from placeholder to thumbnail
-        self.imageOperationQueue.addOperation(imageOperation, forKey: indexPath)
+            if self.appearing
+            {
+                imageOperation.immediate = true
+            }
+            
+            self.imageOperationQueue.addOperation(imageOperation, forKey: indexPath)
+        }        
         
         cell.maximumImageSize = CGSizeMake(self.prototypeCellWidthConstraint.constant, (self.prototypeCellWidthConstraint.constant / 8.0) * 7.0)
         
@@ -293,7 +303,8 @@ extension SaveStatesViewController: UICollectionViewDelegateFlowLayout
 {
     func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize
     {
-        self.configureCollectionViewCell(self.prototypeCell, forIndexPath: indexPath)
+        // No need to load images from disk just to determine size, so we pass true for ignoreExpensiveOperations
+        self.configureCollectionViewCell(self.prototypeCell, forIndexPath: indexPath, ignoreExpensiveOperations: true)
         
         let size = self.prototypeCell.contentView.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize)
         return size

External/Roxas

@@ -1 +1 @@
-Subproject commit 6dc906703bb5870d268d341cefd1fdcc40001eb9
+Subproject commit c795d0ace22cfe57c3b73613630e14b58d2f8f09