ios - 使用 KVO 跟踪 NSProgress

Question

我正在使用 KVO 来跟踪正在接收的文件的进度:

-(void)session:(MCSession *)session didStartReceivingResourceWithName:(NSString *)resourceName fromPeer:(MCPeerID *)peerID withProgress:(NSProgress *)progress

{
NSLog(@"RECEIVING... %@ from peer: %@", progress, peerID);
dispatch_sync(dispatch_get_main_queue(), ^{
    [progress addObserver:self
                forKeyPath:@"fractionCompleted"
                   options:NSKeyValueObservingOptionNew
                   context:NULL];
});}

和

- (void)observeValueForKeyPath:(NSString *)keyPath
                  ofObject:(id)object
                    change:(NSDictionary *)change
                   context:(void *)context
{
if (object == progress) {
    // Handle new fractionCompleted value
[progressBar setProgress:progress.fractionCompleted animated:YES];
    NSLog(@"Fraction Complete: %@", [NSNumber numberWithDouble:progress.fractionCompleted]);
    return;
}

[super observeValueForKeyPath:keyPath
                     ofObject:object
                       change:change
                      context:context];
}

我想用它来更新 UIprogressView...但是代码在这一行崩溃了，我不明白为什么:

[super observeValueForKeyPath:keyPath
                     ofObject:object
                       change:change
                      context:context];

编辑:

这是错误

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason:     '<ViewController1: 0x15b57000>: An -observeValueForKeyPath:ofObject:change:context: message was     received but not handled.

编辑:

如果我删除 super observeValueForKeyPath:keyPath...，应用程序不会崩溃，但 NSLog(@"Fraction Complete: %@ 始终报告值“0”。

Answer 1

您的父类(super class)是否实现了 observeValueForKeyPath:ofObject:change:context: ？你可以做一个 if 检查:

if ([super respondsToSelector:@selector(observeValueForKeyPath:ofObject:change:context:){
    NSLog(@"Yeah, I'm here matey!");
} else {
    NSLog(@"Uh oh said the selector ghost");
}