Must AVAudioPlayer be instantiated from a ViewController class? - objective-c

Question

I'm hoping someone can help as I'm new to iOS / objective C and very puzzled. I'm trying to play a simple sound using AVAudioPlayer as follows:
NSString *path = [[NSBundle mainBundle] pathForResource:#"soundFile" ofType:#"wav"];
NSURL *fileURL = [[NSURL alloc] initFileURLWithPath: path];
self.player=[[AVAudioPlayer alloc] initWithContentsOfURL:fileURL error:NULL];
[self.player play];
I am using ARC so I also have in my .h file, the following reference to my player so that ARC does not deallocate my player prematurely:
#property (nonatomic, strong) AVAudioPlayer *player;
This code works just fine and plays my sound PROVIDED that I run this code from a ViewController or my application's AppDelegate.
However if I cut and paste this very same code, plus all the necessary #includes and the #property and add them into another class in the same application but which is not a ViewController, and call the code there then no error is raised but no sound is played.
It is exactly the same code just called on a different class??
Why would it not work?
I have looked and looked for a similar post but nowhere have I seem exactly this scenario addressed. Many thanks if you can help me- would be much appreciated.
To clarify the issue-- here is how I call this code on another class say a class I have named Audio Tester, I would write in AppDelate say
#import "AppDelegate.h"
#import "AudioTester.h"
#interface AppDelegate ()
#end
#implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
AudioTester * tester = [[AudioTester alloc]init];
[tester playAudio];
}
where AudioTester playAudio is defined as
#import "AudioTester.h"
#implementation AudioTester
-(void) playAudio {
NSString *path = [[NSBundle mainBundle] pathForResource:#"soundFile" ofType:#"wav"];
NSURL *fileURL = [[NSURL alloc] initFileURLWithPath: path];
self.player=[[AVAudioPlayer alloc] initWithContentsOfURL:fileURL error:NULL];
[self.player play];
}
#end
with AudioTester.h as follows
#import <Cocoa/Cocoa.h>
#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>
#interface AudioTester : NSObject
#property (nonatomic, strong) AVAudioPlayer *player;
-(void) playAudio;
#end
Stepping through this code, it gets called just fine but it does not play sound?
If you can help that would be much appreciated. I'm totally stumped.

Answer 1

a little conceptual explanation about your code:
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
AudioTester * tester = [[AudioTester alloc]init];
[tester playAudio];
}
1.
if you use ARC then the instance won't be not kept alive after the scope runs out, therefore the tester object will be immediately released, so in your case the object is deallocated before it could do anything – that is the reason why you can't hear any noise or sound.
if you want to keep your tester instance alive independently from your current scope where you inited in, you need to create like e.g. a property which is outside of the scope; you could put that into a class extension for instance:
#interface AppDelegate ()
// ...
#property (nonatomic, strong, nullable) AVAudioPlayer * tester;
// ...
#end
2.
we don't put anything like this into the AppDelegate.m file, the app delegate class basically handles the app-related events globally like launch, terminate, etc... briefly, the global and major events of the app's life cycle in runtime.
you can read more about its purpose in the official docs.
3.
you may use the –applicationDidFinishLaunching: method deliberately for initing your app, but I feel necessary to mention you may want to put everything inside the method –application:didFinishLaunchingWithOptions: instead.
you can read more about the initial procedure as well in the same documentation.
TL;DR
the answer to your original concern: NO, a class can be inited and instantiated in any other instance of any type of classes in general, but you need to worry about keeping the object alive as long as you want to use it.