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James Bush 74XxB: Untitled snippet

Created by James Bush
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//
//  Created by Nicolas Manzini on 23.01.14.
//  Free under MIT licence
//  Copyright (c) 2014 Nicolas Manzini.
//  Thanks to Daij-Djan for his help
//
//  Modified by James Alan Bush on 01 • 18 • 2017
//

#import <UIKit/UIKit.h>

@interface UIView (Gravity)

@property (nonatomic) BOOL followGravity;

@end

//
//  Created by Nicolas Manzini on 23.01.14.
//  Free under MIT licence
//  Copyright (c) 2014 Nicolas Manzini.
//  Thanks to Daij-Djan for his help
//
//  Modified by James Alan Bush on 01 • 18 • 2017
//


#import "UIView+Gravity.h"
#import <objc/runtime.h>
#import <CoreMotion/CoreMotion.h>
#define ROTATE_90  M_PI_2

@interface GravityManager : CMMotionManager

@property (strong, nonatomic) NSMutableArray * animatedViews;
@property (assign, nonatomic) CGFloat angle;

+ (instancetype)sharedManager;

- (void)addView:(UIView *)view;
- (void)removeView:(UIView *)view;

@end

static char MyCustomPropertyKey  = 0;

@implementation UIView (Gravity)

@dynamic followGravity;

+ (void)load
{
    SEL originalSelector  = NSSelectorFromString(@"dealloc");
    SEL overrideSelector  = @selector(xchg_dealloc);
    Method originalMethod = class_getInstanceMethod(self, originalSelector);
    Method overrideMethod = class_getInstanceMethod(self, overrideSelector);
    
    if (class_addMethod(self, originalSelector, method_getImplementation(overrideMethod), method_getTypeEncoding(overrideMethod)))
    {
        class_replaceMethod(self, overrideSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    }
    else
    {
        method_exchangeImplementations(originalMethod, overrideMethod);
    }
}

- (void)xchg_dealloc
{
    if (self.followGravity)
    {
        [[GravityManager sharedManager] removeView:self];
    }
    objc_setAssociatedObject(self, &MyCustomPropertyKey,  nil, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)setFollowGravity:(BOOL)followGravity
{
    objc_setAssociatedObject(self, &MyCustomPropertyKey,  @(followGravity), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    if (followGravity)
    {
        [[GravityManager sharedManager] addView:self];
    }
    else
    {
        [[GravityManager sharedManager] removeView:self];
    }
}

- (BOOL)followGravity
{
    NSNumber * followGravity = objc_getAssociatedObject(self, &MyCustomPropertyKey);
    // for nil case
    return followGravity ? followGravity.boolValue : NO;
}

@end

@implementation GravityManager

+ (instancetype)sharedManager
{
    static dispatch_once_t pred;
    static GravityManager * sharedManager = nil;
    dispatch_once(&pred, ^
                  {
                      sharedManager               = [[self alloc] init];
                      sharedManager.animatedViews = @[].mutableCopy;
                      sharedManager.deviceMotionUpdateInterval = 0.1;
                      
                      __weak typeof(sharedManager) weakManager = sharedManager;
                      
                      NSOperationQueue *queue = [[NSOperationQueue alloc] init];
                      [sharedManager startDeviceMotionUpdatesToQueue:queue
                                                         withHandler:^(CMDeviceMotion *motion, NSError *error)
                       {
                           double angle = atan2(motion.gravity.x, motion.gravity.y);
                           angle -= ROTATE_90;
                           
                           if (angle != sharedManager.angle)
                           {
                               sharedManager.angle = angle;
                               CGAffineTransform transform = (angle == 0) ? CGAffineTransformIdentity : CGAffineTransformMakeRotation(angle);
                               [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                                   [UIView animateWithDuration:.25
                                                    animations:^{
                                                        [weakManager.animatedViews setValue:[NSValue valueWithCGAffineTransform:transform] forKey:@"transform"];
                                                    }];
                               }];
                           }
                       }];
                  });
    return sharedManager;
}

- (void)addView:(UIView *)view
{
    if([self.animatedViews indexOfObjectIdenticalTo:view] == NSNotFound)
    {
        view.transform =
        (self.angle == 0) ? CGAffineTransformIdentity : CGAffineTransformMakeRotation(self.angle);
        [self.animatedViews addObject:view];
    }
}

- (void)removeView:(UIView *)view
{
    [self.animatedViews removeObject:view];
}



@end

Comments (2)

  1. James Bush

    A modified version of an existing UIView category, which rotates a given view to maintain a parallelism with the horizon as the orientation of an iPhone changes per rotation. This implementation is the most resource-conservative and smoothest of any other.

  2. James Bush

    To use it: Add the category to any implementation file it references the view you want to rotate, and then set the followsGravity property of that view to TRUE.

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