@interface ZXViewController ()

@property (nonatomic, strong) NSProgress *pro;

- (IBAction)btnOnClick:(id)sender;

@end

@implementation ZXViewController

- (void)viewDidLoad

{

    [super viewDidLoad];

    NSProgress *pro = [NSProgress progressWithTotalUnitCount:10000.0];

    // 注册一个监听器  KVO

    [pro addObserver:self forKeyPath:@"fractionCompleted" options:NSKeyValueObservingOptionNew context:nil];

}

- (IBAction)btnOnClick:(id)sender {

    // 模拟改变他的属性

    self.pro.completedUnitCount += 100;

}

// 监听到了属性改变会调用这个方法

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

{

    NSLog(@"lskdjfl=  %f",self.pro.fractionCompleted);

}

@end

iOS NSProgress的使用