NSMutableArray is not instantiated as expected - objective-c

Question

I am developing a class in Objective C which contains two arrays audioFiles and files. Files array contains all the names of the audio files and audioFiles is an array to hold AVAudioFile generated from the items in files array.
I want to instantiate both the array when I create a class instance.
AudioPlayer *player = [[AudioPlayer alloc] init];
But I am unable to instantiate the audioFiles array as its showing nothing (nil). I put both the arrays in the implementation because I don't want to expose these two arrays outside of my class.
Could you please help me to fix the problem?
#import <AVFoundation/AVFoundation.h>
#import "AudioPlayer.h"
#implementation AudioPlayer
{
NSMutableArray *audioFiles;
NSArray *files;
}
- (instancetype)init
{
self = [super init];
if (self) {
files = [NSArray arrayWithObjects:#"one", #"two", #"three",#"four", nil];
[self createAudioFiles];
}
return self;
}
-(void) createAudioFiles{
for (int i = 0; i < [files count]; i++) {
NSString *audioPath = [[NSBundle mainBundle] files[i] ofType:#"wav"];
NSURL *url = [NSURL fileURLWithPath:audioPath];
AVAudioFile *file = [[AVAudioFile alloc] initForReading:url error:nil];
[audioFiles addObject:file];
}
}
#end

Answer 1

You are not initializing the audioFiles at all, you need to add:
audioFiles = [NSMutableArray array];
to your init or at the beginning of createAudioFiles method.
If you don't plan to add more objects after initialization, there is no need to keep the array mutable though, just declare it as NSArray *audioFiles; and change your method to:
-(void) createAudioFiles{
NSMutableArray *buffer = [NSMutableArray array];
for (int i = 0; i < [files count]; i++) {
NSString *audioPath = [[NSBundle mainBundle] files[i] ofType:#"wav"];
NSURL *url = [NSURL fileURLWithPath:audioPath];
AVAudioFile *file = [[AVAudioFile alloc] initForReading:url error:nil];
[buffer addObject:file];
}
audioFiles = [buffer copy]; // make it immutable
}