UIDynamic-物理引擎

@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); // 二维向量，表示方向。另一个确定方向还有 angle 属性
gravity.magnitude = 1; // 重力加速度。加速度越大，碰撞越厉害
[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：

物理仿真元素：遵循UIDynamicItem协议的对象；

物理仿真行为：继承UIDynamicBehavior，UIDynamic提供了

    UIGravityBehavior-重力行为

    UICollisionBehavior-碰撞行为

    UISnapBehavior-捕捉行为

    UIPushBehavior-推动行为

    UIAttachmentBehavior-附着行为

    UIDynamicItemBehavior-动力元素行为

物理仿真器：让物理仿真元素执行具体的物理仿真行为，它是UIDynamicAnimator类型的对象；

步骤：

创建物理仿真器，设置仿真范围；

创建物理仿真行为，添加物理仿真元素；

将物理仿真行为添加到物理仿真器中，开始仿真；

注意：

如果要进行连续的捕捉行为，需要先把前面的捕捉行为从物理仿真器中移除；

    [self.animator removeAllBehaviors];

    [self.animator addBehavior:snap];