AVAudiounit: I can't play a sound with an effect like delay - ios

Question

I'm new to objective c and try to code a programm which can play a sound with an effect on it, like a reverb or delay. Unfortunately I'm only able to play the sound, but without the effect. I'm stuck for 3 days now and can't find a solution. Does anyone can tell what I'm doing wrong?
I tried this code, but with it there's no sound at all:
- (void)viewDidLoad {
[super viewDidLoad];
AVAudioEngine *engine = [AVAudioEngine new];
AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];
playerA.volume = 0.5;
NSURL *Mia1url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"MIA1" ofType:#"m4a"]];
AVAudioFile *MIA1 = [[AVAudioFile alloc] initForReading:Mia1url error:nil];
AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:MIA1.processingFormat frameCapacity:1024];
[MIA1 readIntoBuffer:buffer error:nil];
AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
delay.delayTime = 100;
delay.wetDryMix = 90;
[engine attachNode:playerA];
[engine attachNode:delay];
[engine connect: playerA to: delay format:MIA1.processingFormat];
[engine connect: delay to: engine.mainMixerNode format: MIA1.processingFormat];
[playerA scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];
[engine prepare];
[engine startAndReturnError:nil];
[playerA play];
}
after that I tried this code but the sound is only coming without the effect:
- (void)viewDidLoad {
[super viewDidLoad];
AVAudioEngine *engine = [AVAudioEngine new];
AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];
playerA.volume = 0.5;
NSURL *Mia1url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"MIA1" ofType:#"m4a"]];
AVAudioFile *MIA1 = [[AVAudioFile alloc] initForReading:Mia1url error:nil];
AVAudioPCMBuffer *buffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:MIA1.processingFormat frameCapacity:1024];
[MIA1 readIntoBuffer:buffer error:nil];
AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
delay.delayTime = 100;
delay.wetDryMix = 90;
[engine attachNode:playerA];
[engine attachNode:delay];
[engine connect: playerA to: delay format:MIA1.processingFormat];
[engine connect: delay to: engine.mainMixerNode format: MIA1.processingFormat];
[playerA scheduleBuffer:buffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];
[engine prepare];
[engine startAndReturnError:nil];
//change
self.playerA = [[AVAudioPlayer alloc] initWithContentsOfURL:Mia1url error:nil];
//change from [playerA play] to:
[self.playerA play];
}

Answer 1

You forgot to instantiate your objects:
//AVAudioEngine *engine; // no instance exists.
AVAudioEngine *engine = [AVAudioEngine new];
AVAudioPlayerNode *playerA = [AVAudioPlayerNode new];
...
AVAudioUnitDelay *delay = [AVAudioUnitDelay new];
...
Also, you have to initialize playerA only once and before using it.
For digging deeper you might want to checkout Apples code samples.