Trouble hooking up AVAudioUnitEffect with AVAudioEngine

Question

I've been poking around with AVAudioEngine and I'm having trouble integrating AVAudioUnitEffect classes. For example, with AVAudioUnitDelay...

@implementation ViewController {
AVAudioEngine *engine;
AVAudioPlayerNode *player;
}

...

- (IBAction)playButtonHit:(id)sender {
if (!player){
    NSURL *bandsURL = [[NSBundle mainBundle] URLForResource:@"Bands With Managers" withExtension:@"mp3"];
    AVAudioFile *file = [[AVAudioFile alloc] initForReading:bandsURL error:nil];

    engine = [[AVAudioEngine alloc] init];
    player = [[AVAudioPlayerNode alloc] init];
    [engine attachNode:player];

    AVAudioUnitDelay *delay = [[AVAudioUnitDelay alloc] init];
    delay.wetDryMix = 50;

    [engine connect:player to:delay format:file.processingFormat];
    [engine connect:delay to:[engine outputNode] format:file.processingFormat];

    [player scheduleFile:file atTime:nil completionHandler:nil];
    [engine prepare];
    [engine startAndReturnError:nil];
}
[player play];  

}

When the method is called the app crashes and I get this error: "* Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: [_nodes containsObject: node1] && [_nodes containsObject: node2]'"

I'm modeling this after some of the examples from the "AVAudioEngine in Practice" session from WWDC. I know there's probably something obvious I'm missing but can't figure it out....

Answer 1

You forgot to attach your AvAudioUnitDelay object to your AvAudioEngine nodes before linking them ;)

Here is the working code :

- (IBAction)playMusic:(id)sender {
    if (!player){
        NSURL *bandsURL = [[NSBundle mainBundle] URLForResource:@"Bands With Managers" withExtension:@"mp3"];
        AVAudioFile *file = [[AVAudioFile alloc] initForReading:bandsURL error:nil];

        engine = [[AVAudioEngine alloc] init];
        player = [[AVAudioPlayerNode alloc] init];
        [engine attachNode:player];

        AVAudioUnitDelay *delay = [[AVAudioUnitDelay alloc] init];
        delay.wetDryMix = 50;
        [engine attachNode:delay]; 

        [engine connect:player to:delay format:file.processingFormat];
        [engine connect:delay to:[engine outputNode] format:file.processingFormat];

        [player scheduleFile:file atTime:nil completionHandler:nil];
        [engine prepare];
        [engine startAndReturnError:nil];
    }
    [player play]; 
}