addObserver:forKeyPath is crashing the app, KVO, objective c - objective-c

Question

I am doing the parallax effect by using category by doing :
add and UIView into the uitableView (via category
add addObserver:forKeyPath so that whenever tableview is moving, i will reframe the view above
Details are below
UIScrollView+Parallax.h
#import <UIKit/UIKit.h>
#class ParallaxView;
#interface UIScrollView (Parallax)
#property (strong, nonatomic) ParallaxView *parallaxView;
- (void) addParallaxViewWith:(UIView*)parallaxView;
- (void) removeKVO;
#end
#interface ParallaxView : UIView
#end
UIScrollView+Parallax.m
static char parallaxKey;
#implementation UIScrollView (Parallax)
#dynamic parallaxView;
#pragma mark - Add parallax view to scrollView
- (void) addParallaxViewWith:(ParallaxView*)pView {
if ( !self.parallaxView) {
[self addSubview:pView];
[self setParallaxView:pView];
}
}
#pragma mark - Set parallaxView + register parallaxView as an observer
- (void) setParallaxView:(ParallaxView *)parallaxView {
objc_setAssociatedObject(self, &parallaxKey, parallaxView, OBJC_ASSOCIATION_ASSIGN);
/* THESE LINE ARE CRASHING THE APP */
// [self addObserver:self.parallaxView
// forKeyPath:#"contentOffset"
// options:NSKeyValueObservingOptionNew
// context:nil];
}
#pragma mark - Get parallaxView
- (ParallaxView*) parallaxView {
return (objc_getAssociatedObject(self, &parallaxKey));
}
#pragma mark - Remove
- (void)removeKVO {
[self removeObserver:self.parallaxView forKeyPath:#"contentOffset"];
}
#end
#implementation ParallaxView
-(id)init
{
//load xib from main bundle and assign it to self
self = [[[NSBundle mainBundle]loadNibNamed:#"Parallex"
owner:self
options:nil] objectAtIndex:0];
return self;
}
-(id)initWithFrame:(CGRect)frame
{
self = [self init];
[self setFrame:frame];
return self;
}
................
#end
And I am adding parallax to the table by doing
ParallaxView *pView = [[ParallaxView alloc]initWithFrame:CGRectMake(0, 0, 320, 160)];
[self.tableView addParallaxViewWith:pView];
However, [self addObserver:forKeyPath:options:context:nil] keeps crashing the app without no clues at all. If I comments this line out and app is not crashing but parallex effect is not working.
Any ideas for this problematics. Please help. Thanks

Answer 1

Problem in code
-(id)initWithFrame:(CGRect)frame
{
self = [self init];
[self setFrame:frame];
return self;
}
In above code self = [self init]; and [self setFrame:frame]; will go in recursion will give crash
,First fix this I guess it will solve your problem,It should be like this
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
and also loading View from nib using
self = [[[NSBundle mainBundle]loadNibNamed:#"Parallex"
owner:self
options:nil] objectAtIndex:0];
this code is really a bad idea.
you can refer THIS for this task.
Happy and clean coding...

Answer 2

#implementation ParallaxView
//Add Observe Method
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
if([keyPath isEqualToString:#"contentOffset"]){
NSLog(#"contentOffset:%#", [change objectForKey:NSKeyValueChangeNewKey]);
}
}
#end
Try to replace
objc_setAssociatedObject(self, &parallaxKey, parallaxView, OBJC_ASSOCIATION_ASSIGN);
with
//Change to OBJC_ASSOCIATION_RETAIN_NONATOMIC
objc_setAssociatedObject(self, &parallaxKey, parallaxView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
parallaxView should be a strong reference.