UIKit動力學（三）

 

#import <UIKit/UIKit.h>

@interface DragViewController : UICollectionViewController

@end

#import "DragViewController.h"
#import "DragLayout.h"

@implementation DragViewController

- (NSInteger)collectionView:(UICollectionView *)collectionView
     numberOfItemsInSection:(NSInteger)section {
    return 70;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    return [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
}

//對不一樣手勢處理
- (IBAction)handleLongPress:(UIGestureRecognizer *)g {
    DragLayout *dragLayout = (DragLayout *)self.collectionViewLayout;
    CGPoint location = [g locationInView:self.collectionView];
    
    // Find the indexPath and cell being dragged
    NSIndexPath *indexPath = [self.collectionView
                              indexPathForItemAtPoint:location];
    UICollectionViewCell *cell = [self.collectionView
                                  cellForItemAtIndexPath:indexPath];
    
    UIGestureRecognizerState state = g.state;
    if (state == UIGestureRecognizerStateBegan) {
        // Change the color and start dragging   開始拖曳動做
        [UIView animateWithDuration:0.25
                         animations:^{
//
                             cell.backgroundColor = [UIColor colorWithRed:arc4random_uniform(255)/255.0 green:arc4random_uniform(255)/255.0 blue:arc4random_uniform(255)/255.0 alpha:1];
                             cell.layer.cornerRadius =10;
                             
                         }];
        [dragLayout startDraggingIndexPath:indexPath fromPoint:location];//傳入所點擊項目
    }
    //手勢釋放時 
    else if (state == UIGestureRecognizerStateEnded ||
             state == UIGestureRecognizerStateCancelled) {
        // Change the color and stop dragging
        [UIView animateWithDuration:0.25
                         animations:^{
                             cell.backgroundColor = [UIColor colorWithRed:arc4random_uniform(255)/255.0 green:arc4random_uniform(255)/255.0 blue:arc4random_uniform(255)/255.0 alpha:1];
                
                             
                         }];
        //無手勢處理
        [dragLayout stopDragging];
    }
    
    else {
        // Drag 拖曳必定距離
        [dragLayout updateDragLocation:location];
    }
}

@end

#import <UIKit/UIKit.h>

@interface DragLayout : UICollectionViewFlowLayout
- (void)startDraggingIndexPath:(NSIndexPath *)indexPath
                     fromPoint:(CGPoint)p;
- (void)updateDragLocation:(CGPoint)point;
- (void)stopDragging;
@end

#import "DragLayout.h"

@interface DragLayout ()

@property (nonatomic) NSIndexPath *indexPath;
@property (nonatomic) UIDynamicAnimator *animator;
@property (nonatomic) UIAttachmentBehavior *behavior;

@end

@implementation DragLayout
//開始拖曳 添加動力學效果 修改The anchor point for the attachment behavior
- (void)startDraggingIndexPath:(NSIndexPath *)indexPath
                     fromPoint:(CGPoint)p {
  self.indexPath = indexPath;
  self.animator = [[UIDynamicAnimator alloc]
                   initWithCollectionViewLayout:self];

  UICollectionViewLayoutAttributes *attributes = [super layoutAttributesForItemAtIndexPath:self.indexPath];
  
    // Raise the item above its peers 把該項目提到其餘項目之上
  attributes.zIndex += 1;

  self.behavior = [[UIAttachmentBehavior alloc] initWithItem:attributes
                                            attachedToAnchor:p];
  self.behavior.length = 0;
  self.behavior.frequency = 10;//晃動頻率
  [self.animator addBehavior:self.behavior];

  // Add a little resistance to keep things stable
  UIDynamicItemBehavior *dynamicItem = [[UIDynamicItemBehavior alloc]
                                        initWithItems:@[attributes]];
  dynamicItem.resistance = 10;
  [self.animator addBehavior:dynamicItem];

  [self updateDragLocation:p];
}

- (void)updateDragLocation:(CGPoint)p {
  self.behavior.anchorPoint = p;
}
//手勢中止
- (void)stopDragging {
  // Move back to the original location (super) 回到原始位置
  UICollectionViewLayoutAttributes *
  attributes = [super layoutAttributesForItemAtIndexPath:self.indexPath];//所點擊indexPath center
  [self updateDragLocation:attributes.center];
  self.indexPath = nil;
  self.behavior = nil;
}
//返回rect中的全部的元素的佈局屬性
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
  // Find all the attributes, and replace the one for our indexPath  找到全部屬性，並替換indexPath中的
  NSArray *existingAttributes = [super
                                 layoutAttributesForElementsInRect:rect];
  NSMutableArray *allAttributes = [NSMutableArray new];
  for (UICollectionViewLayoutAttributes *a in existingAttributes) {
    if (![a.indexPath isEqual:self.indexPath]) {
      [allAttributes addObject:a];
    }
  }

  [allAttributes addObjectsFromArray:[self.animator itemsInRect:rect]];
  return allAttributes;
}

@end