An instance 0xca90200 of class UILabel was deallocated while key value observers were still registered with it

一個錯誤，大意是UILabel被內(nèi)存釋放后，它得值依然在被觀察

原因是給UILabel增加了個監(jiān)聽事件

[self.valueLabel addObserver:self
                  forKeyPath:@"text"
                     options:NSKeyValueObservingOptionNew
                     context:nil];

然后在UIView被pop后，監(jiān)聽時間沒有停止，解決辦法為：
- (void)dealloc
{
[_valueLabel removeObserver:self forKeyPath:@"text"];
}