Question

我已经设置了KVO通知来观看UIWebView的某些属性，如此

[webView addObserver:self 
          forKeyPath:@"canGoBack"
             options:NSKeyValueObservingOptionNew
             context:NULL];

并且

- (void)observeValueForKeyPath:(NSString *)keyPath 
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context

但它永远不会被调用。我错过了什么或UIWebView是不可观察的？

Answer 1

canGoBack是readonly属性：为了使其符合KVO，它必须在其实现中将该属性重新声明为readwrite，然后通过合成的setter设置该属性。我怀疑canGoBack只是通过它的ivar设置，它不会通过KVO系统发送通知：

[self setCanGoBack:YES]; // Would notify KVO observers (as long as any reimplementation of automaticallyNotifiesObserversForKey does place restrictions)
_canGoBack = YES; // Would not notify KVO observers

此相关问题详细讨论了该问题：Is it possible to observe a readonly property of an object in Cocoa Touch?

作为一种变通方法，您可以设置UIWebViewDelegate并检查[UIWebView canGoBack]中[UIWebViewDelegate webViewDidFinishLoad:]的值。

UIWebView KVO是否合规？

1 个答案: