检测UIWebView滚动视图的contentSize的更改

时间:2012-11-08 18:52:25

标签: ios user-interface uiscrollview contentsize

我正在尝试在UIScrollView内容的底部设置一个UIView,这样做我将视图的位置设置为scrollview的contentsize高度。但是我的scrollview是UIWebView的子视图,因此当加载图像时,内容大小会发生变化,我应该位于scrollview底部的视图最终会在中间...

所以我正在寻找一种在scrollview的内容化更改时得到通知的方法。我试图将其子类化并更改contentize的setter以发送NSNotification:

@implementation UIScrollView (Height)

-(void)setContentSize:(CGSize)contentSize
{
    _contentSize=contentSize;
    [[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:@"scrollViewContentSizeChanged" object:nil]];
}

@end

但是在编译时我得到并且错误地说:

  

“_ OBJC_IVAR _ $ _ UIScrollView._contentSize”,引自:          - MyClass.o中的[UIScrollView(Heigth)setContentSize:]   ld:找不到架构armv7的符号

知道如何将setter子类化吗?

谢谢!

2 个答案:

答案 0 :(得分:29)

也许您可以使用键值观察(KVO)来检测内容大小的变化。我没试过,但代码应该是这样的:

static int kObservingContentSizeChangesContext;

- (void)startObservingContentSizeChangesInWebView:(UIWebView *)webView {
    [webView.scrollView addObserver:self forKeyPath:@"contentSize" options:0 context:&kObservingContentSizeChangesContext];
}

- (void)stopObservingContentSizeChangesInWebView:(UIWebView *)webView {
    [webView.scrollView removeObserver:self forKeyPath:@"contentSize" context:&kObservingContentSizeChangesContext];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if (context == &kObservingContentSizeChangesContext) {
        UIScrollView *scrollView = object;
        NSLog(@"%@ contentSize changed to %@", scrollView, NSStringFromCGSize(scrollView.contentSize));
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

如果这不起作用,您可能需要调整setContentSize:方法。方法调配让你的替换方法调用原始方法,这是将新内容大小传递给滚动视图所需要做的。

您可以在此处详细了解方法调整:http://www.mikeash.com/pyblog/friday-qa-2010-01-29-method-replacement-for-fun-and-profit.html

我认为这是最流行的代码:https://github.com/rentzsch/jrswizzle

答案 1 :(得分:3)

你的方法是正确的。您可以通过类别覆盖现有方法,但不能访问类中的ivar。

在这种情况下,您需要的是方法调配:您覆盖setContentSize,同时保持对方法的原始实现的引用,因此您可以调用它来设置_contentSize

以下是您可以使用的代码,其中包含注释:

@implementation UIScrollView (Height)

// -- this method is a generic swizzling workhorse
// -- it will swap one method impl with another and keep the old one
// under your own impl name
+ (void)swizzleMethod:(SEL)originalSel andMethod:(SEL)swizzledSel {

  Method original = class_getInstanceMethod(self, originalSel);
  Method swizzled = class_getInstanceMethod(self, swizzledSel);
  if (original && swizzled)
     method_exchangeImplementations(original, swizzled);
  else
    NSLog(@"Swizzling Fault: methods not found.");

}    

//-- this is called on the very moment when the categoty is loaded
//-- and it will ensure the swizzling is done; as you see, I am swapping
//-- setContentSize and setContentSizeSwizzled;
+ (void)load {
  [self swizzleMethod:@selector(setContentSize:) andMethod:@selector(setContentSizeSwizzled:)];
}

//-- this is my setContentSizeSwizzled implementation;
//-- I can still call the original implementation of the method
//-- which will be avaiable (*after swizzling*) as setContentSizeSwizzled
//-- this is a bit counterintuitive, but correct!
- (void)setContentSizeSwizzled:(CGSize)contentSize
{
  [self setContentSizeSwizzled:contentSize];
  [[NSNotificationCenter defaultCenter] postNotification:[NSNotification    notificationWithName:@"scrollViewContentSizeChanged" object:nil]];
}

@end

希望它有所帮助。