Merge pull request #2093 from xamarin/fix-2068

Make UWP FilePicker FutureAccessList more robust

Author: jfversluis

Xamarin.Essentials/FilePicker/FilePicker.uwp.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
 using Windows.Storage;
@@ -35,12 +36,51 @@ static async Task<IEnumerable<FileResult>> PlatformPickAsync(PickOptions options
                     resultList.Add(file);
             }
 
-            foreach (var file in resultList)
-                StorageApplicationPermissions.FutureAccessList.Add(file);
+            AddToAndCleanUpFutureAccessList(resultList);
 
             return resultList.Select(storageFile => new FileResult(storageFile));
         }
 
+        static void AddToAndCleanUpFutureAccessList(List<StorageFile> pickedFiles)
+        {
+            var fal = StorageApplicationPermissions.FutureAccessList;
+
+            try
+            {
+                // Check if (FutureAccessList current items + new picked files) is exceeding maximum items
+                if ((fal.Entries.Count + pickedFiles.Count) >= fal.MaximumItemsAllowed)
+                {
+                    // We assume that the FutureAccessList items are saved in order, there is no metadata
+                    // Therefore we start removing from the bottom of the list
+                    var removeCount = Math.Min(fal.Entries.Count, pickedFiles.Count);
+                    var falTokens = fal.Entries.TakeLast(removeCount).ToList();
+
+                    foreach (var entry in falTokens)
+                    {
+                        fal.Remove(entry.Token);
+                    }
+                }
+
+                // Check if the picked file count doesn't exceed the maximum, else take the last n number or picked files
+                var pickedFilesLimitedToMax = pickedFiles;
+                if (pickedFiles.Count > StorageApplicationPermissions.FutureAccessList.MaximumItemsAllowed)
+                {
+                    pickedFilesLimitedToMax =
+                        pickedFilesLimitedToMax.TakeLast((int)fal.MaximumItemsAllowed).ToList();
+                }
+
+                foreach (var file in pickedFilesLimitedToMax)
+                {
+                    StorageApplicationPermissions.FutureAccessList.Add(file);
+                }
+            }
+            catch (Exception ex)
+            {
+                // Just log, we don't want to break on this
+                Debug.WriteLine($"Error adding to/cleaning up FutureAccessList: {ex.Message}");
+            }
+        }
+
         static void SetFileTypes(PickOptions options, FileOpenPicker picker)
         {
             var hasAtLeastOneType = false;