无法获得以编程方式更改的约束

我试图获得滚动视差效果。以下代码是CollectionViewCell的代码。无法获得以编程方式更改的约束

#import "NearbyViewCell.h" 

@interface NearbyViewCell() 

@property (nonatomic) CGFloat parallaxOffset; 

@end 
@implementation NearbyViewCell 

- (id)initWithFrame:(CGRect)frame 
{ 
    self = [super initWithFrame:frame]; 
    if (self) { 

     self.clipsToBounds = YES; 

     self.locationImage = [[UIImageView alloc] initWithFrame:CGRectMake(0.0, 0.0, frame.size.width, frame.size.height)]; 
     self.locationImage.frame = self.contentView.bounds; 
     self.locationImage.contentMode = UIViewContentModeScaleAspectFill; 

     self.locationLabel = [[UILabel alloc] initWithFrame:CGRectMake(0.0, 0.0, frame.size.width, frame.size.height - 50.0)]; 
     self.locationLabel.numberOfLines = 0; 
     self.locationLabel.textAlignment = NSTextAlignmentCenter; 
     self.locationLabel.textColor = [UIColor whiteColor]; 
     self.locationLabel.backgroundColor = [UIColor colorWithRed:0.0/255.0 green:0.0/255.0 blue:0.0 /255.0 alpha:0.5]; 


     self.otherLabel = [[UILabel alloc] initWithFrame:CGRectMake(0.0, (frame.size.height - 50.0), frame.size.width, 50.0)]; 
     self.otherLabel.textAlignment = NSTextAlignmentCenter; 
     self.otherLabel.textColor = [UIColor whiteColor]; 
     self.otherLabel.backgroundColor = [UIColor colorWithRed:0.0/255.0 green:0.0/255.0 blue:0.0 /255.0 alpha:0.5]; 

     [self.contentView addSubview:self.locationImage]; 
     [self.contentView addSubview:self.locationLabel]; 
     [self.contentView addSubview:self.otherLabel]; 
    } 
    return self; 
}

以下代码是从collectionViewController的scrollViewDidScroll中调用的。该约束是一个IBOutlet，并在头文件中声明。

- (void)updateParallaxOffset:(CGRect)bounds { 
    CGPoint center = CGPointMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds)); 
    CGPoint offsetFromCenter = CGPointMake(center.x - self.center.x, center.y - self.center.y); 
    CGFloat maxVerticalOffset = (CGRectGetHeight(bounds)/2) + (CGRectGetHeight(self.bounds)/2); 
    CGFloat scaleFactor = 4000/maxVerticalOffset; 

    self.parallaxOffset = -offsetFromCenter.y * scaleFactor; 

    self.locationLabelCenterYConstraint.constant = self.parallaxOffset; 
    NSLog(@"%f", self.locationLabelCenterYConstraint.constant); 
    NSLog(@"%f", self.parallaxOffset); 
} 

@end

的问题是，“parallaxOffset”的值发生变化，但“locationLabelCenterYConstraint”的值并没有改变。下面给出NSLog的结果。

2016-01-13 22:55:43.926 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:43.926 Parallax[1597:382314] -161.566707 
2016-01-13 22:55:43.926 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:43.926 Parallax[1597:382314] 1307.221542 
2016-01-13 22:55:43.926 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:43.927 Parallax[1597:382314] 2776.009792 
2016-01-13 22:55:44.108 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:44.108 Parallax[1597:382314] -3094.247246 
2016-01-13 22:55:44.109 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:44.109 Parallax[1597:382314] -1625.458996 
2016-01-13 22:55:44.110 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:44.110 Parallax[1597:382314] -156.670747 
2016-01-13 22:55:44.110 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:44.111 Parallax[1597:382314] 1312.117503 
2016-01-13 22:55:44.118 Parallax[1597:382314] 0.000000 
2016-01-13 22:55:44.118 Parallax[1597:382314] 2780.905753

谢谢您提前！

来源

2016-01-13 Vishisht Tiwari

我已经得到了这个工作，通过编程添加约束而不是通过接口生成器。这现在工作正常。

来源

2016-01-13 23:23:30

无法获得以编程方式更改的约束

回答

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