Question

I am a newbie in Objective-C. I am trying to learn how to work with NSStream. I just used simple code from Apple Support. This code should open a stream from a file in my Desktop and show a simple message when the delegate is called by iStream. At the end of the code, I can see the status is correct, but the delegate never gets called. What am I missing?

#import <Foundation/Foundation.h>

@interface MyDelegate: NSStream <NSStreamDelegate>{
}

- (void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)eventCode ;

@end

@implementation MyDelegate

- (void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)eventCode  {
    NSLog(@"############# in DELEGATE###############");
}

@end

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        MyDelegate* myDelegate=[[MyDelegate alloc]init];
        NSInputStream* iStream= [[NSInputStream alloc] initWithFileAtPath:@"/Users/Augend/Desktop/Test.rtf"];

        [iStream setDelegate:myDelegate];

        [iStream scheduleInRunLoop:[NSRunLoop currentRunLoop]
                           forMode:NSDefaultRunLoopMode];
        [iStream open];

        NSLog(@" status:%@",(NSString*) [iStream streamError]);
    }
    return 0;
}

Answer 1

The run loop isn’t running long enough for the delegate method to be called.

Add:

[[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:2.0]];

right after you open the stream. This is only necessary in a program without a GUI — otherwise the run loop would be spun for you.

If you want to be absolutely sure that stream:handleEvent: has been called before exiting, set a (global) flag in that method and put the runUntilDate: in a while loop that tests for the flag:

while( !delegateHasBeenNotified ){
     [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.5]];
}