如何从 KVO 方法 observeValueForKeyPath:ofObject:change:context: 中的更改字典中获取 int 值？

Question

我正在通过调用以下方法来观察 AVPlayer rate 属性 的变化：

addObserver:sharedPlayerManagerInstance
 forKeyPath:@"rate"
    options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld
    context:0]; 

因此，我从 observeValueForKeyPath:ofObject:change:context: 得到的 change 字典是：

change = { kind: 1,
            new: 1,
            old: 0 }

我检查了每个值的class，原来是__NSCFNumber。但是，当我尝试将 [change objectForKey:@"new"] 或 [change objectForKey:@"old"] 转换为 int、NSInteger、NSNumber，甚至尝试过 NSString 等时，它对 "old" 有效，但它给了我一个解析错误"new":

error: expected a type
error: 1 errors parsing expression

真要对比一下，想不通。这可能是 iOS 中的错误吗？

Answer 1

Objective C

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
NSNumber * newValue = [change objectForKey:NSKeyValueChangeNewKey];
NSInteger integerValue = newValue.integerValue;
int intValue = newValue.intValue;
}

Swift

   override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
        if let newValue = change[NSKeyValueChangeNewKey] as? NSNumber{
            let intvalue = newValue.intValue //To int
        }
    }

Answer 2

Swift 3:

if let newValue = change?[NSKeyValueChangeKey.newKey] as? NSNumber {
     // Do stuff
}