CAGradientLayer in UITableViewCell

Question

I have a UITableViewCell that has an UIView (gradientView) where I want to apply the gradient. This cell has AutoLayout, and so I want to update the gradient frame when the gradientView frame changes.

I have tried the following, but none of them worked:

-(void)layoutSubviews{
    [super layoutSubviews];
     self.gradient.frame = self.gradientView.bounds;
}

-(void)updateConstraints{
    [super updateConstraints];
    self.gradient.frame = self.gradientView.bounds;
}

-(void)updateConstraintsIfNeeded{
    [super updateConstraintsIfNeeded];
    self.gradient.frame = self.gradientView.bounds;
}

also I can't use this inside the cell:

- (void)viewDidLayoutSubviews{}

Kegluneq Kegluneq · Accepted Answer · 2014-12-03T14:35:03

Personally I always use KVO for changing layers frame. Put this line after cell subviews has been loaded (-(void)awakeFromNib if you're using IB/storyboards). It's important that this line will be called only once in cells lifetime!

[self.gradientView.layer addObserver:self forKeyPath:@"bounds" options:NSKeyValueObservingOptionNew context:nil];

then just implement this method:

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    if(object==self.gradientView.layer && self.gradient.superlayer!=nil){
        CGRect newFrame = [change[NSKeyValueChangeNewKey] CGRectValue];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.gradient.frame = newFrame;
        });
    }
}

I put frame update in dispatch_async block since without it layer was not updated.

And don't forget to remove observer eg. in dealloc:

-(void)dealloc{
    [self.gradientView.layer removeObserver:self forKeyPath:@"bounds"];
}

CAGradientLayer in UITableViewCell

2 Answers