UIKit動力學（一）

@interface ViewController : UIViewController

@end

/*物理仿真元素
 
 注意：
 
 不是任何對象都能作物理仿真元素
 
 不是任何對象都能進行物理仿真
 
 
 物理仿真元素要素：
 
 任何遵照了UIDynamicItem協議的對象
 
 UIView默認已經遵照了UIDynamicItem協議，所以任何UI控件都能作物理仿真
 
 UICollectionViewLayoutAttributes類默認也遵照UIDynamicItem協議
 
 */

#import "ViewController.h"
@import QuartzCore;

const CGPoint kInitialPoint1 = { .x = 33, .y = 250 };
const CGPoint kInitialPoint2 = { .x = 150, .y = 250 };

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIView *box1;
@property (weak, nonatomic) IBOutlet UIView *box2;
@property (nonatomic) UIDynamicAnimator *dynamicAnimator;
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  self.dynamicAnimator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

  [self reset];
}

- (IBAction)reset {
  [self.dynamicAnimator removeAllBehaviors];
    self.box1.center = kInitialPoint1;
    self.box1.layer.cornerRadius = 10;
    self.box1.layer.borderWidth = 2;
    self.box1.layer.borderColor = [[UIColor blackColor]CGColor];
    self.box1.transform = CGAffineTransformIdentity;
    
    self.box2.center = kInitialPoint2;
    self.box2.layer.cornerRadius = 10;
    self.box2.layer.borderWidth = 2;
    self.box2.layer.borderColor = [[UIColor greenColor]CGColor];
    self.box2.transform = CGAffineTransformIdentity;
}

- (IBAction)snap {//迅速移動行爲(捕捉行爲)
  CGPoint point = [self randomPoint];
  UISnapBehavior/*物理仿真行爲*/ *snap = [[UISnapBehavior alloc] initWithItem:self.box1//物理仿真元素 要作動畫的元素
                                                  snapToPoint:point];
  snap.damping = 0.25;//阻尼係數   移動後的彈動幅度
  [self addTemporaryBehavior:snap];
}

- (IBAction)attach {//附着行爲 ？？？
    UIAttachmentBehavior *attach1 = [[UIAttachmentBehavior alloc] initWithItem:self.box1
                                                              offsetFromCenter:UIOffsetMake(50, 50)//旋轉點
                                                              attachedToAnchor:self.box1.center];
    [self.dynamicAnimator addBehavior:attach1];
    
    
   
    UIAttachmentBehavior *attach2 = [[UIAttachmentBehavior alloc] initWithItem:self.box2
                                                                attachedToItem:self.box1];
    [self.dynamicAnimator addBehavior:attach2];
    
      UIPushBehavior *push = [[UIPushBehavior alloc] initWithItems:@[self.box2]
                                                              mode:UIPushBehaviorModeInstantaneous];
      push.pushDirection = CGVectorMake(0, 2);
      [self.dynamicAnimator addBehavior:push];
    
}

- (IBAction)push {//推進行爲
  UIPushBehavior *push = [[UIPushBehavior alloc] initWithItems:@[self.box1]
                                                          mode:UIPushBehaviorModeContinuous];
  push.pushDirection = CGVectorMake(1, 1);
//    CGVectorMake(0垂直方向 數值越大越往右偏移, 推進速度)
  [self.dynamicAnimator addBehavior:push];
}

- (IBAction)gravity {//重力行爲
  UIGravityBehavior *gravity = [[UIGravityBehavior alloc] initWithItems:@[self.box1]];
  gravity.action = ^{
    NSLog(@"%@", NSStringFromCGPoint(self.box1.center));
  };
  [self.dynamicAnimator addBehavior:gravity];
}

- (IBAction)collision {//碰撞行爲
    UICollisionBehavior *collision = [[UICollisionBehavior alloc] initWithItems:@[self.box1,
                                                                                  self.box2]];
    [self.dynamicAnimator addBehavior:collision];
    
    UIPushBehavior *push = [[UIPushBehavior alloc] initWithItems:@[self.box1]
                                                            mode:UIPushBehaviorModeInstantaneous];
    push.pushDirection = CGVectorMake(3, 0);
    collision.action = ^{//行爲中添加操做
        if (self.box2.center.x-self.box2.frame.size.width/2 > self.view.frame.size.width){
            [self reset];
        }
    };
    [self addTemporaryBehavior:push];
   
}

- (void)addTemporaryBehavior:(UIDynamicBehavior *)behavior {
  [self.dynamicAnimator/*物理仿真器 實施行爲的引擎*/ addBehavior:behavior];
  [self.dynamicAnimator performSelector:@selector(removeBehavior:)
                             withObject:behavior
                             afterDelay:1];
}

- (CGPoint)randomPoint {
  CGSize size = self.view.bounds.size;
  return CGPointMake(arc4random_uniform(size.width),
                     arc4random_uniform(size.height));
}

@end