如何正确观察我的scrollView子类的contentOffset属性? [英] How do I properly observe the contentOffset property of my scrollView subclass?

问题描述

在我的iOS应用中，我正在观察对scrollView子类的contentOffset属性的更改.我的观察员处理程序如下所示:

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);

}

为简单起见，我任意选择方法的参数作为 id .

I chose the parameter to the method arbitrarily as an id for simplicity.

我的NSLog'ging看起来像这样:

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}

我需要使用x和y值，但我不知道如何获得它们.我试过将ID投射到CGPoint，不.我试过将参数更改为CGPoint，不.

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.

它变得更深. @mgold不高兴.这是我设置观察值的方法:

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];

观察者是我用来简化观察的便捷类.注意观察者回调 observeContentOffsetHandler:.当我从当前方法更改此方法的签名时:

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

@mgold对CGPoint的建议:

to @mgold's suggestion of CGPoint:

- (void)observeContentOffsetHandler:(CGPoint)aContentOffset

这是不正确的，因为NSLog显示aContentOffset的全零:

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

不知道我在这里做什么.

Not sure what my move here is.

推荐答案

知道了.该方法的正确签名为:

Got it. The method correct signature is:

- (void)observeContentOffsetHandler:(NSValue *)aContentOffset

然后检索CGPoint很简​​单:

Retrieval of the CGPoint is then trivial:

CGPoint pt = [aContentOffset CGPointValue];

干杯，
道格

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