Added dynamic springy.

iOS7ScrollViews.xcodeproj/project.pbxproj

@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		046DAB2517D57C9700A079C8 /* SVSpingyFlowLayout.m in Sources */ = {isa = PBXBuildFile; fileRef = 046DAB2417D57C9700A079C8 /* SVSpingyFlowLayout.m */; };
 		497F9368177371D6005B8A3C /* UIKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 497F9367177371D6005B8A3C /* UIKit.framework */; };
 		497F936A177371D6005B8A3C /* Foundation.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 497F9369177371D6005B8A3C /* Foundation.framework */; };
 		497F936C177371D6005B8A3C /* CoreGraphics.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 497F936B177371D6005B8A3C /* CoreGraphics.framework */; };
@@ -22,6 +23,8 @@
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
+		046DAB2317D57C9700A079C8 /* SVSpingyFlowLayout.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SVSpingyFlowLayout.h; sourceTree = "<group>"; };
+		046DAB2417D57C9700A079C8 /* SVSpingyFlowLayout.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SVSpingyFlowLayout.m; sourceTree = "<group>"; };
 		497F9364177371D6005B8A3C /* iOS7ScrollViews.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = iOS7ScrollViews.app; sourceTree = BUILT_PRODUCTS_DIR; };
 		497F9367177371D6005B8A3C /* UIKit.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = UIKit.framework; path = System/Library/Frameworks/UIKit.framework; sourceTree = SDKROOT; };
 		497F9369177371D6005B8A3C /* Foundation.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = Foundation.framework; path = System/Library/Frameworks/Foundation.framework; sourceTree = SDKROOT; };
@@ -90,6 +93,8 @@
 				497F9377177371D6005B8A3C /* SVAppDelegate.m */,
 				497F93841773723D005B8A3C /* SVViewController.h */,
 				497F93851773723D005B8A3C /* SVViewController.m */,
+				046DAB2317D57C9700A079C8 /* SVSpingyFlowLayout.h */,
+				046DAB2417D57C9700A079C8 /* SVSpingyFlowLayout.m */,
 				497F93861773723D005B8A3C /* SVViewController.xib */,
 				497F9389177372A1005B8A3C /* SVScrollingCell.h */,
 				497F938A177372A1005B8A3C /* SVScrollingCell.m */,
@@ -181,6 +186,7 @@
 			files = (
 				497F9374177371D6005B8A3C /* main.m in Sources */,
 				497F9378177371D6005B8A3C /* SVAppDelegate.m in Sources */,
+				046DAB2517D57C9700A079C8 /* SVSpingyFlowLayout.m in Sources */,
 				497F93871773723D005B8A3C /* SVViewController.m in Sources */,
 				497F938B177372A1005B8A3C /* SVScrollingCell.m in Sources */,
 			);
@@ -295,6 +301,7 @@
 				497F9383177371D6005B8A3C /* Release */,
 			);
 			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Release;
 		};
 /* End XCConfigurationList section */
 	};

iOS7ScrollViews/SVSpingyFlowLayout.h

@@ -0,0 +1,13 @@
+//
+//  SVSpingyFlowLayout.h
+//  iOS7ScrollViews
+//
+//  Created by Kyle Fang on 9/3/13.
+//  Copyright (c) 2013 Pierre Felgines. All rights reserved.
+//
+
+#import <UIKit/UIKit.h>
+
+@interface SVSpingyFlowLayout : UICollectionViewFlowLayout
+
+@end

iOS7ScrollViews/SVSpingyFlowLayout.m

@@ -0,0 +1,72 @@
+//
+//  SVSpingyFlowLayout.m
+//  iOS7ScrollViews
+//
+//  Created by Kyle Fang on 9/3/13.
+//  Copyright (c) 2013 Pierre Felgines. All rights reserved.
+//
+
+#import "SVSpingyFlowLayout.h"
+
+@implementation SVSpingyFlowLayout{
+    UIDynamicAnimator *_dynamicAnimator;
+}
+
+- (void)prepareLayout{
+    [super prepareLayout];
+    CGSize contentSize = [self collectionViewContentSize];
+    NSArray *items = [super layoutAttributesForElementsInRect:CGRectMake(0, 0, contentSize.width, contentSize.height)];
+    
+    if (!_dynamicAnimator) {
+        _dynamicAnimator = [[UIDynamicAnimator alloc] initWithCollectionViewLayout:self];
+        for (UICollectionViewLayoutAttributes *item in items) {
+            UIAttachmentBehavior *spring = [[[UIAttachmentBehavior alloc] initWithItem:item attachedToAnchor:item.center] retain];
+            spring.length = 0.f;
+            spring.damping = 0.5;
+            spring.frequency = 0.8;
+            [_dynamicAnimator addBehavior:spring];
+        }
+        
+    }
+    
+
+}
+
+- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
+    return [_dynamicAnimator itemsInRect:rect];
+}
+
+- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
+    return [_dynamicAnimator layoutAttributesForCellAtIndexPath:indexPath];
+}
+
+- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
+    
+    UIScrollView *scrollView = self.collectionView;
+    CGFloat scrolledDelta = newBounds.origin.y - scrollView.bounds.origin.y;
+    
+    CGPoint touchPoint = [scrollView.panGestureRecognizer locationInView:scrollView];
+    
+    for (UIAttachmentBehavior *spring in _dynamicAnimator.behaviors) {
+        CGPoint anchorPoint = spring.anchorPoint;
+        CGFloat distanceFromTouch = fabsf(anchorPoint.y - touchPoint.y);
+        CGFloat scrollResistance = distanceFromTouch / 500.f;
+        
+        UICollectionViewLayoutAttributes *item = [spring.items firstObject];
+        CGPoint center = item.center;
+        center.y += scrolledDelta * MIN(1, scrollResistance);
+        item.center = center;
+        
+        [_dynamicAnimator updateItemUsingCurrentState:item];
+        
+    }
+    
+    return NO;
+}
+
+- (void)dealloc{
+    _dynamicAnimator = nil;
+    [super dealloc];
+}
+
+@end