Collision not working between items

问题

I'm using UIDynamics in my app. my app has two squares. one is fixed and the other can be moved (by applying a pan gesture). when i try to collide them they don't collide. the delegate methods never get called. here's my code and i hope someone can point out the problem.

    UIDynamicAnimator* animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
  UICollisionBehavior* collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.square1, self.square2]];
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;

    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    [self.square1 addGestureRecognizer:pan];
    [collisionBehavior setCollisionMode:UICollisionBehaviorModeEverything];
    [animator addBehavior:collisionBehavior];
    collisionBehavior.collisionDelegate = self;

回答1:

Make animator as a property or instance variable. otherwise it will be cleared after view load.
Make sure implemented UICollisionBehaviorDelegate protol and correspond methods

Here is my works implementation based on your code.

Interface:

#import <UIKit/UIKit.h>

@interface DynamicViewController : UIViewController<UICollisionBehaviorDelegate>

@property (strong, nonatomic) UIDynamicAnimator *animator;

@property (strong, nonatomic) UIPushBehavior *pushBehavior;

@end

Implementation:

@synthesize pushBehavior = _pushBehavior;
@synthesize animator = _animator;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIView *square1 = [[UIView alloc] initWithFrame:CGRectMake(100, 30, 30, 30)];
    square1.center = CGPointMake(150, 150);
    square1.backgroundColor = [UIColor greenColor];
    UIView *square2 = [[UIView alloc] initWithFrame:CGRectMake(100, 300, 30, 30)];
    square2.center = CGPointMake(250, 350);
    square2.backgroundColor = [UIColor redColor];
    [self.view addSubview:square1];
    [self.view addSubview:square2];

    _animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

    UICollisionBehavior* collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[square1, square2]];
    collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    [collisionBehavior setCollisionMode:UICollisionBehaviorModeEverything];
    collisionBehavior.collisionDelegate = self;
    [_animator addBehavior:collisionBehavior];

    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    [square1 addGestureRecognizer:pan];
}

#pragma mark push behavior
- (void)handlePan:(UIPanGestureRecognizer *)gesture
{
    if(gesture.state == UIGestureRecognizerStateBegan){
        if (_pushBehavior) {
            [_animator removeBehavior:_pushBehavior];
        }
        _pushBehavior = [[UIPushBehavior alloc] initWithItems:@[gesture.view] mode:UIPushBehaviorModeContinuous];
        [_animator addBehavior:_pushBehavior];
    }

    CGPoint offset =[gesture translationInView:self.view];
    _pushBehavior.pushDirection = CGVectorMake(offset.x,offset.y);
    _pushBehavior.magnitude = sqrtf(offset.x * offset.x + offset.y * offset.y) / 50;
    if (gesture.state == UIGestureRecognizerStateEnded) {
        [_animator removeBehavior:_pushBehavior];
        _pushBehavior = nil;
    }
}

#pragma mark Colision delegate
- (void)collisionBehavior:(UICollisionBehavior*)behavior beganContactForItem:(id <UIDynamicItem>)item1 withItem:(id <UIDynamicItem>)item2 atPoint:(CGPoint)p;
{
    NSLog(@"Colision Began");
}
- (void)collisionBehavior:(UICollisionBehavior*)behavior endedContactForItem:(id <UIDynamicItem>)item1 withItem:(id <UIDynamicItem>)item2;
{
  NSLog(@"Colision End");
}

回答2:

Your UIDynamicAnimator* animator is destroyed when function ends due to ARC. Thats why you are not able to see any animations. Make it a instance variable and you will be fine.

回答3:

I think there is some bug with UIDynamics (but not 100% sure let me know if I'm wrong). I couldn't make my dynamic works until I created instance variables for UIDynamicAnimator and UIGravityBehavior. Try add instance variable to the .m file in class extension as:

UIDynamicAnimator* animator;
UICollisionBehavior* collisionBehavior;

And change your first two line of code to:

animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[self.square1, self.square2]];

It should help.

回答4:

You have to specify the bounds using "addBoundaryWithIdentifier" for the collision class and remove the non-moving item form the collision

来源：https://stackoverflow.com/questions/20769593/collision-not-working-between-items

标签

ios

objective-c

uikit-dynamics

uicollisionbehavior