[Objective C中的iOS属性观察器（字符串或字典）

Question

我正在为我的应用构建属性观察器（键值观察）。理想的情况是监视值的奇异值（字符串或字典）。我已经在viewDidLoad

中写过

@interface BarScannerViewController () <AVCaptureMetadataOutputObjectsDelegate>
{
    NSMutableDictionary *scanTrackingNumbers;   
}

和viewdidload

[scanTrackingNumbers addObserver:self forKeyPath:@"scanTrackingNumber" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

[scanTrackingNumbers setValue:@"test123455" forKey:@"scanTrackingNumber"];

并实现方法

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{

    if ([keyPath isEqualToString:@"scanTrackingNumber"]){
        NSLog(@"scanTrackingNumber Changed %@",change);
        NSLog(@"scan12335 %@",scanTrackingNumbers);
    }
}

我不知道为什么它不起作用（注意打印到控制台日志）。代码可能有什么问题？

Answer 1

Answer 2