观察NSProgress

Question

我正在使用此代码跟踪NSProgress中的更改号码：

[progress addObserver:self forKeyPath:kProgressCancelledKeyPath options:NSKeyValueObservingOptionNew context:NULL];


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
NSProgress *progress = object;
NSLog(@"PROG: %f", progress.fractionCompleted);
// Check which KVO key change has fired
if ([keyPath isEqualToString:kProgressCancelledKeyPath]) {
    // Notify the delegate that the progress was cancelled
}
else if ([keyPath isEqualToString:kProgressCompletedUnitCountKeyPath]) {
    // Notify the delegate of our progress change
    NSLog(@"PROG: %f", progress.fractionCompleted);
    if (progress.completedUnitCount == progress.totalUnitCount) {
        // Progress completed, notify delegate
        NSLog(@"PROG: %f", progress.fractionCompleted);
    }
}
}

这就是我得到的：

<NSProgress: phase=Loading; state=Waiting; fractionCompleted=0.000000> from peer: <MCPeerID: 0x14e1f220 DisplayName = alessandro's iPod touch-593288>

注意到更多。我想使用已完成分数的进度视图，但我没有得到任何价值。从未调用过NSlog PROG ......