Fix handling of deleted photos on iOS (#1556)

* Fix crash on iOS when images are deleted

Fixes a crash on iOS when a displayed image is deleted in the
background:

    NSInternalInconsistencyException
    reason: 'attempt to delete and reload the same index path <snip>'

According to
https://developer.apple.com/documentation/photokit/phfetchresultchangedetails?language=objc

    ...changedIndexes can't be used safely inside
    performBatchUpdates:completion: Instead, use changedIndexes after and
    outside the performBatchUpdates:completion: call...

* Update selection when assets are removed from collection

If a selected photo is deleted from the photo library, it needs to be
removed from `selectedAssets` or the UI will hang when the user taps
"Done". Also, the UI needs to be updated to reflect the new selection.

* Update counts in footer when collection changes

When the number of photos or videos in the collection changes, update
the footer to reflect the new counts.

Author: brsaylor2

ios/QBImagePicker/QBImagePicker/QBAssetsViewController.m

@@ -417,15 +417,31 @@ - (void)photoLibraryDidChange:(PHChange *)changeInstance
                     if ([insertedIndexes count]) {
                         [self.collectionView insertItemsAtIndexPaths:[insertedIndexes qb_indexPathsFromIndexesWithSection:0]];
                     }
-
-                    NSIndexSet *changedIndexes = [collectionChanges changedIndexes];
-                    if ([changedIndexes count]) {
-                        [self.collectionView reloadItemsAtIndexPaths:[changedIndexes qb_indexPathsFromIndexesWithSection:0]];
-                    }
                 } completion:NULL];
+
+                NSIndexSet *changedIndexes = [collectionChanges changedIndexes];
+                if ([changedIndexes count]) {
+                    [self.collectionView reloadItemsAtIndexPaths:[changedIndexes qb_indexPathsFromIndexesWithSection:0]];
+                }
             }
 
             [self resetCachedAssets];
+
+            // Update the selection to remove any assets that have been removed from the collection
+            NSMutableSet *removedAssets = [NSMutableSet new];
+            for (PHAsset *asset in self.imagePickerController.selectedAssets) {
+                if(![self.fetchResult containsObject:asset]) {
+                    [removedAssets addObject:asset];
+                }
+            }
+            [self removeAssetsFromSelection:removedAssets];
+
+            // Update the footer to show the current photo/video counts
+            NSArray<UICollectionReusableView *> *footers =
+                [self.collectionView visibleSupplementaryViewsOfKind:UICollectionElementKindSectionFooter];
+            if (footers.count) {
+                [self updateFooterView:footers[0]];
+            }
         }
     });
 }
@@ -507,57 +523,60 @@ - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView
         UICollectionReusableView *footerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter
                                                                                   withReuseIdentifier:@"FooterView"
                                                                                          forIndexPath:indexPath];
+        [self updateFooterView:footerView];
 
-        // Number of assets
-        UILabel *label = (UILabel *)[footerView viewWithTag:1];
+        return footerView;
+    }
 
-        NSBundle *bundle = self.imagePickerController.assetBundle;
-        NSUInteger numberOfPhotos = [self.fetchResult countOfAssetsWithMediaType:PHAssetMediaTypeImage];
-        NSUInteger numberOfVideos = [self.fetchResult countOfAssetsWithMediaType:PHAssetMediaTypeVideo];
+    return nil;
+}
 
-        switch (self.imagePickerController.mediaType) {
-            case QBImagePickerMediaTypeAny:
-            {
-                NSString *format;
-                if (numberOfPhotos == 1) {
-                    if (numberOfVideos == 1) {
-                        format = NSLocalizedStringFromTableInBundle(@"assets.footer.photo-and-video", @"QBImagePicker", bundle, nil);
-                    } else {
-                        format = NSLocalizedStringFromTableInBundle(@"assets.footer.photo-and-videos", @"QBImagePicker", bundle, nil);
-                    }
-                } else if (numberOfVideos == 1) {
-                    format = NSLocalizedStringFromTableInBundle(@"assets.footer.photos-and-video", @"QBImagePicker", bundle, nil);
+- (void)updateFooterView:(UICollectionReusableView *)footerView {
+    // Number of assets
+    UILabel *label = (UILabel *)[footerView viewWithTag:1];
+
+    NSBundle *bundle = self.imagePickerController.assetBundle;
+    NSUInteger numberOfPhotos = [self.fetchResult countOfAssetsWithMediaType:PHAssetMediaTypeImage];
+    NSUInteger numberOfVideos = [self.fetchResult countOfAssetsWithMediaType:PHAssetMediaTypeVideo];
+
+    switch (self.imagePickerController.mediaType) {
+        case QBImagePickerMediaTypeAny:
+        {
+            NSString *format;
+            if (numberOfPhotos == 1) {
+                if (numberOfVideos == 1) {
+                    format = NSLocalizedStringFromTableInBundle(@"assets.footer.photo-and-video", @"QBImagePicker", bundle, nil);
                 } else {
-                    format = NSLocalizedStringFromTableInBundle(@"assets.footer.photos-and-videos", @"QBImagePicker", bundle, nil);
+                    format = NSLocalizedStringFromTableInBundle(@"assets.footer.photo-and-videos", @"QBImagePicker", bundle, nil);
                 }
-
-                label.text = [NSString stringWithFormat:format, numberOfPhotos, numberOfVideos];
+            } else if (numberOfVideos == 1) {
+                format = NSLocalizedStringFromTableInBundle(@"assets.footer.photos-and-video", @"QBImagePicker", bundle, nil);
+            } else {
+                format = NSLocalizedStringFromTableInBundle(@"assets.footer.photos-and-videos", @"QBImagePicker", bundle, nil);
             }
-                break;
 
-            case QBImagePickerMediaTypeImage:
-            {
-                NSString *key = (numberOfPhotos == 1) ? @"assets.footer.photo" : @"assets.footer.photos";
-                NSString *format = NSLocalizedStringFromTableInBundle(key, @"QBImagePicker", bundle, nil);
-
-                label.text = [NSString stringWithFormat:format, numberOfPhotos];
-            }
-                break;
+            label.text = [NSString stringWithFormat:format, numberOfPhotos, numberOfVideos];
+        }
+            break;
 
-            case QBImagePickerMediaTypeVideo:
-            {
-                NSString *key = (numberOfVideos == 1) ? @"assets.footer.video" : @"assets.footer.videos";
-                NSString *format = NSLocalizedStringFromTableInBundle(key, @"QBImagePicker", bundle, nil);
+        case QBImagePickerMediaTypeImage:
+        {
+            NSString *key = (numberOfPhotos == 1) ? @"assets.footer.photo" : @"assets.footer.photos";
+            NSString *format = NSLocalizedStringFromTableInBundle(key, @"QBImagePicker", bundle, nil);
 
-                label.text = [NSString stringWithFormat:format, numberOfVideos];
-            }
-                break;
+            label.text = [NSString stringWithFormat:format, numberOfPhotos];
         }
+            break;
 
-        return footerView;
-    }
+        case QBImagePickerMediaTypeVideo:
+        {
+            NSString *key = (numberOfVideos == 1) ? @"assets.footer.video" : @"assets.footer.videos";
+            NSString *format = NSLocalizedStringFromTableInBundle(key, @"QBImagePicker", bundle, nil);
 
-    return nil;
+            label.text = [NSString stringWithFormat:format, numberOfVideos];
+        }
+            break;
+    }
 }
 
 
@@ -653,6 +672,32 @@ - (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndex
     }
 }
 
+- (void)removeAssetsFromSelection:(NSSet *)assets
+{
+    if (assets.count == 0) {
+        return;
+    }
+
+    QBImagePickerController *imagePickerController = self.imagePickerController;
+    NSMutableOrderedSet *selectedAssets = imagePickerController.selectedAssets;
+
+    // Remove assets from set
+    [selectedAssets minusSet:assets];
+
+    self.lastSelectedItemIndexPath = nil;
+
+    [self updateDoneButtonState];
+
+    if (self.imagePickerController.showsNumberOfSelectedAssets) {
+        [self updateSelectionInfo];
+
+        if (selectedAssets.count == 0) {
+            // Hide toolbar
+            [self.navigationController setToolbarHidden:YES animated:YES];
+        }
+    }
+}
+
 
 #pragma mark - UICollectionViewDelegateFlowLayout