UIDynamic-實體引擎

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIView *redView;
@property (weak, nonatomic) IBOutlet UISegmentedControl *segment;
@property (weak, nonatomic) IBOutlet UIProgressView *progressView;

@property (nonatomic, strong) UIDynamicAnimator *animator;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.redView.transform = CGAffineTransformMakeRotation(M_PI_4);
}

- (void)touchesBegan:(NSSet
   
     *)touches withEvent:(UIEvent *)event {
//    [self testGravity];
    
//    [self testGravityAndCollision];
    
//    [self testGravityAndCollision2];
    
//    [self testGravityAndCollision3];
    
    [self testSnap:touches];
}

- (void)testGravity {
    UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
    [gravity addItem:self.redView];
    
    [self.animator addBehavior:gravity];
}

- (void)testGravityAndCollision {
    UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
    gravity.gravityDirection = CGVectorMake(0, 1); // 二維向量，表示方向。另一個确定方向還有 angle 屬性
    gravity.magnitude = 1; // 重力加速度。加速度越大，碰撞越厲害
    [gravity addItem:self.redView];
    
    UICollisionBehavior *collision = [[UICollisionBehavior alloc] init];
    collision.translatesReferenceBoundsIntoBoundary = YES;
    [collision addItem:self.redView];
    [collision addItem:self.progressView];
    [collision addItem:self.segment];
    
    [self.animator addBehavior:gravity];
    [self.animator addBehavior:collision];
}

- (void)testGravityAndCollision2 {
    UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
    [gravity addItem:self.redView];
    
    [self.animator addBehavior:gravity];
    
    UICollisionBehavior *collision = [[UICollisionBehavior alloc] init];
    [collision addBoundaryWithIdentifier:@"line1" fromPoint:CGPointMake(0, 160) toPoint:CGPointMake(320, 400)];
    [collision addBoundaryWithIdentifier:@"line2" fromPoint:CGPointMake(320, 0) toPoint:CGPointMake(320, 400)];
    [collision addItem:self.redView];
    
    [self.animator addBehavior:collision];
}

- (void)testGravityAndCollision3 {
    UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
    [gravity addItem:self.redView];
    
    [self.animator addBehavior:gravity];
    
    UICollisionBehavior *collision = [[UICollisionBehavior alloc] init];
    [collision addBoundaryWithIdentifier:@"circle" forPath:[UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 320, 320)]];
    [collision addItem:self.redView];
    
    [self.animator addBehavior:collision];
}

- (void) testSnap:(NSSet
    
      *)touches {
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:touch.view];
    
    UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:self.redView snapToPoint:point];
    snap.damping = arc4random_uniform(10) / 10.0;
    
    [self.animator removeAllBehaviors];
    [self.animator addBehavior:snap];
}

- (UIDynamicAnimator *)animator {
    if (_animator == nil) {
        _animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    }
    return _animator;
}

@end

    
   
           

概念： 實體仿真元素：遵循UIDynamicItem協定的對象； 實體仿真行為：繼承UIDynamicBehavior，UIDynamic提供了     UIGravityBehavior-重力行為     UICollisionBehavior-碰撞行為     UISnapBehavior-捕捉行為     UIPushBehavior-推動行為     UIAttachmentBehavior-附着行為     UIDynamicItemBehavior-動力元素行為 實體仿真器：讓實體仿真元素執行具體的實體仿真行為，它是UIDynamicAnimator類型的對象；

步驟： 建立實體仿真器，設定仿真範圍； 建立實體仿真行為，添加實體仿真元素； 将實體仿真行為添加到實體仿真器中，開始仿真；

注意： 如果要進行連續的捕捉行為，需要先把前面的捕捉行為從實體仿真器中移除；     [self.animator removeAllBehaviors];     [self.animator addBehavior:snap];