NSFileHandle readInBackgroundAndNotify does not work

问题

Hi I'm using NSFileHandle's readInBackgroundAndNotify method to get notifications when a log file has been updated.

I have the following code:

- (void)startReading
{
    NSString *logPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Library/Logs/MyTestApp.log"];
    NSFileHandle *fh = [NSFileHandle fileHandleForReadingAtPath:logPath];
    NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
    [notificationCenter addObserver:self
                           selector:@selector(getData:)
                               name:NSFileHandleReadCompletionNotification
                             object:fh];
    [fh readInBackgroundAndNotify];
}

- (void) getData: (NSNotification *)aNotification
{
     NSLog(@"notification received");
}

However the selector is never called and the notification is not received.

回答1:

1. Add an NSLog to startReading to make sure that's getting called.
2. Log fh. My guess is that it's nil (most probably because you haven't created MyTestApp.log yet).

来源：https://stackoverflow.com/questions/1324152/nsfilehandle-readinbackgroundandnotify-does-not-work