objective-c : snapBehavior example code

snippet.m

//snapBehavior example code

@implementation DynamicSandwichViewController
{
    NSMutableArray* _views;
    UISnapBehavior* _snap;
    BOOL _viewDocked;
}


- (void)someMethod
{
    [self tryDockView:someView]; //executes tryDockView: method
}


//선택된 뷰 이외 나머지 뷰의 알파값 변경 (투명 뷰로 만들기)
//show and hide the non-docked views so that the docked view occupies the entire screen 
- (void)setAlphaWhenViewDocked:(UIView*)view alpha:(CGFloat)alpha {
    for (UIView* aView in _views) {
        if (aView != view) {
            aView.alpha = alpha;
        }
    }
}


//checks whether the view has been dragged close to the top of the screen
//if it has, and the view is not yet docked
//creates a UISnapBehaviour which snaps the view to the center of the screen.
- (void)tryDockView:(UIView *)view {
    
    BOOL viewHasReachedDockLocation = (view.frame.origin.y < 150.0);
    
    if (viewHasReachedDockLocation) {
        if (!_viewDocked) {
            _snap = [[UISnapBehavior alloc] initWithItem:view snapToPoint:self.view.center];
            [_animator addBehavior:_snap];
            [self setAlphaWhenViewDocked:view alpha:0.0];
            _viewDocked = YES;
        }
        
        
    } else {
        
        //If the view has been dragged away from the top of the screen and was previously docked
        //removes the snap behavior (as a result view falls due to the gravity)
        
        if (_viewDocked) {
            [_animator removeBehavior:_snap];
            
            [UIView animateWithDuration:0.3 animations:^{
                [self setAlphaWhenViewDocked:view alpha:1.0];
            }];
            
            
            _viewDocked = NO;
        }
    }
}


@end