In my iOS app I am observing changes to the contentOffset property of my scrollView subclass. My observer handler looks like this:
- (void)observeContentOffsetHandler:(id)aContentOffset {
NSLog(@"%@", aContentOffset);
}
I chose the parameter to the method arbitrarily as an id for simplicity.
My NSLog'ging looks like this:
-[MyScrollView observeContentOffsetHandler:] [Line 111] NSPoint: {296, 375}
-[MyScrollView observeContentOffsetHandler:] [Line 111] NSPoint: {296, 389}
-[MyScrollView observeContentOffsetHandler:] [Line 111] NSPoint: {295, 401}
-[MyScrollView observeContentOffsetHandler:] [Line 111] NSPoint: {291, 415}
I need to use the x and y values but I have no idea how to get at them. I've tried casting the id to a CGPoint, nope. I've tried changing the param to a CGPoint, nope.
UPDATE
It gets deeper. @mgold no joy. Here is how I set up observation:
self.contentOffsetObserver = [[[Observer alloc] initWithTarget:self action:@selector(observeContentOffsetHandler:)] autorelease];
[self.myScrollViewSubclass addObserver:self.contentOffsetObserver forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew context:NULL];
Observer is a handy class I use to make observation easy. Note the observer callback observeContentOffsetHandler:. When I change the signature of this method from its current:
- (void)observeContentOffsetHandler:(id)aContentOffset
to @mgold's suggestion of CGPoint:
- (void)observeContentOffsetHandler:(CGPoint)aContentOffset
It is incorrect as NSLog shows with all zeros for aContentOffset:
-[MyScrollController observeContentOffsetHandler:] [Line 74] aContentOffset 0 0
-[MyScrollController observeContentOffsetHandler:] [Line 74] aContentOffset 0 0
-[MyScrollController observeContentOffsetHandler:] [Line 74] aContentOffset 0 0
-[MyScrollController observeContentOffsetHandler:] [Line 74] aContentOffset 0 0
Not sure what my move here is.
Got it. The method correct signature is:
Retrieval of the CGPoint is then trivial:
Cheers,
Doug
contentoffset
is indeed aCGPoint
, which is a C struct withCGFloat
sx
andy
. So simplyBecause you are subclassing
UIScrollView
, you also have thecontentoffset
property, just saying.Since you have a UIScrollView subclass, you have access to layoutSubViews
It is called every time contentOffset changes.
That is the "proper way" to get the changes as they happen. Don't use KVO Yes contentOffset is a CGPoint....unless you were talking about NSScrollView.....but even then the basic idea stays same.
Override layoutSubviews....remember to call super
OR
register your ViewController as delegate of the scrollView and implement scrollView:didScroll