optimize tasks

Pixiview/Illust/IllustCollectionPage.cs

@@ -75,6 +75,7 @@ namespace Pixiview.Illust
         protected double topOffset;
 
         private T illustData;
+        private ParallelTask task;
 
         public IllustCollectionPage()
         {
@@ -95,6 +96,11 @@ namespace Pixiview.Illust
 
         public override void OnUnload()
         {
+            if (task != null)
+            {
+                task.Dispose();
+                task = null;
+            }
             InvalidateCollection();
             Illusts = null;
             lastUpdated = default;
@@ -559,7 +565,12 @@ namespace Pixiview.Illust
 
         void DoLoadImages(IllustCollection collection)
         {
-            ParallelTask.Start(0, collection.Count, Configs.MaxThreads, i =>
+            if (task != null)
+            {
+                task.Dispose();
+                task = null;
+            }
+            task = ParallelTask.Start(0, collection.Count, Configs.MaxThreads, i =>
             {
                 if (!collection.Running)
                 {
@@ -716,11 +727,17 @@ namespace Pixiview.Illust
         }
 
         private readonly object sync = new object();
-        private volatile bool running;
+        private bool running;
 
         public bool Running
         {
-            get => running;
+            get
+            {
+                lock (sync)
+                {
+                    return running;
+                }
+            }
             set
             {
                 lock (sync)

Pixiview/Illust/UserIllustPage.xaml.cs

@@ -109,13 +109,6 @@ namespace Pixiview.Illust
                 return;
             }
             await ScrollToTopAsync(scrollView);
-            // release
-            var collection = IllustCollection;
-            if (collection != null)
-            {
-                collection.Running = false;
-                IllustCollection = null;
-            }
             startIndex = -1;
             nextIndex = 0;
             illustIds = null;

Pixiview/Illust/ViewIllustPage.xaml.cs

@@ -128,6 +128,7 @@ namespace Pixiview.Illust
         private readonly ImageSource fontIconNotLove;
         private IllustUgoiraData ugoiraData;
         private Ugoira ugoira;
+        private ParallelTask task;
 
         private readonly object sync = new object();
         private int downloaded = 0;
@@ -188,6 +189,15 @@ namespace Pixiview.Illust
             }
         }
 
+        public override void OnUnload()
+        {
+            if (task != null)
+            {
+                task.Dispose();
+                task = null;
+            }
+        }
+
 #if __IOS__
         protected override void OnPageTopMarginChanged(Thickness old, Thickness @new)
         {
@@ -387,7 +397,12 @@ namespace Pixiview.Illust
                 }
             }
 
-            ParallelTask.Start(0, items.Length, Configs.MaxPageThreads, i =>
+            if (task != null)
+            {
+                task.Dispose();
+                task = null;
+            }
+            task = ParallelTask.Start(0, items.Length, Configs.MaxPageThreads, i =>
             {
                 DoLoadImage(i);
                 return true;
@@ -461,7 +476,6 @@ namespace Pixiview.Illust
             else
             {
                 var val = downloaded / (float)pageCount;
-                App.DebugPrint($"download progress: {val}");
                 MainThread.BeginInvokeOnMainThread(() =>
                 {
                     ViewExtensions.CancelAnimations(progress);