feat(ios): improved cell size computation

BREAKING CHANGE: this needs testing to ensure it does not break anything for fixed size and dynamic size templates

Author: farfromrefug

packages/collectionview/platforms/ios/src/Info.plist

@@ -0,0 +1,2 @@
+#import <UIKit/UIKit.h>
+#import "UICollectionViewCacheDelegateFlowLayout.h"

packages/collectionview/platforms/ios/src/NSCollectionView.h

@@ -0,0 +1,6 @@
+@interface UICollectionViewCacheDelegateFlowLayout: NSObject <UICollectionViewDelegateFlowLayout>
+
+@property (nonatomic, retain) NSMutableArray* cachedSizes;
+
+- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout computedSizeForItemAtIndexPath:(NSIndexPath *)indexPath;
+@end

packages/collectionview/platforms/ios/src/UICollectionViewCacheDelegateFlowLayout.h

@@ -0,0 +1,36 @@
+#import "UICollectionViewCacheDelegateFlowLayout.h"
+
+@implementation UICollectionViewCacheDelegateFlowLayout
+@synthesize cachedSizes;
+- (instancetype)init
+{
+  self = [super init];
+  if (self) {
+    self.cachedSizes = [NSMutableArray new];
+  }
+  return self;
+}
+- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout computedSizeForItemAtIndexPath:(NSIndexPath *)indexPath
+{
+    return CGSizeZero;
+}
+
+- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
+{
+  NSInteger index = indexPath.row;
+  if (index < [self.cachedSizes count]) {
+      NSValue* value =  [self.cachedSizes objectAtIndex:indexPath.row];
+      if (value != nil && !CGSizeEqualToSize([value CGSizeValue], CGSizeZero)) {
+          return [value CGSizeValue];
+      }
+    CGSize size = [self collectionView:collectionView layout:collectionViewLayout computedSizeForItemAtIndexPath:indexPath];
+    [self.cachedSizes replaceObjectAtIndex:indexPath.row withObject:[NSValue valueWithCGSize:size]];
+    return size;
+  } else {
+    CGSize size = [self collectionView:collectionView layout:collectionViewLayout computedSizeForItemAtIndexPath:indexPath];
+    [self.cachedSizes addObject:[NSValue valueWithCGSize:size]];
+    return size;
+  }
+}
+
+@end

packages/collectionview/platforms/ios/src/UICollectionViewCacheDelegateFlowLayout.m

@@ -0,0 +1,5 @@
+module NSCollectionView {
+  umbrella header "NSCollectionView.h"
+  export *
+  module * { export * }
+}

packages/collectionview/platforms/ios/src/module.modulemap

@@ -1,2 +1,3 @@
 /// <reference path="./typings/arv.d.ts" />
 /// <reference path="./typings/android.d.ts" />
+/// <reference path="./typings/ios.d.ts" />

src/collectionview/index.ios.ts

@@ -0,0 +1,3 @@
+declare class UICollectionViewCacheDelegateFlowLayout extends NSObject implements UICollectionViewDelegateFlowLayout {
+    cachedSizes: NSMutableArray;
+}

src/collectionview/references.d.ts

@@ -54,7 +54,7 @@ export default function install() {
             layout['minimumInteritemSpacing'] = 0;
             return layout;
         },
-        createDelegate: () => UICollectionViewWaterfallDelegateImpl.new()
+        createDelegate: (collectionview: CollectionView) => UICollectionViewWaterfallDelegateImpl.new()
     });
     CollectionView.registerPlugin('waterfall', {
         onLayout: (collectionview: CollectionView) => {