如何在iOS中拥有永久视图？

Question

We are using a UInavigationController with one of the views being one that plays soundtracks.

We are using the AVfountation framework.

We navigate to audiolist(where music is played) on button click

-(IBAction)audioBtnClicked
{
    audiolist *audio=[[audiolist alloc] initWithNibName:@"audiolist" bundle:nil];
    [self.navigationController pushViewContrller:audio animated:YES];
    [audiolist release];
}

When the user plays music and navigates away, the music continues playing

Problem: when the user navigates back to the list of songs and plays another track, 2 songs are playing at the same time.

We think that a new instance of audiolist is created everytime the user navigates back. We would like to only have one instance of audiolist . How do we make the first instance of audiolist persistent and how do we refer back to it?

Answer 1

You have to do

[audio release];

and not

[audiolist release];

audiolist seems to be your class name. The naming conventions says that classes should be capital and camel-cased, so it should be AudioList. It'll make your code more readable.

To have one single shared instance of your AudioList, you could do this:

Add a class method to your header:

+ (AudioList *) sharedInstance;

then add this to your implementation file:

@implementation AudioList

static AudioList *gSharedInstance = nil;

+ (AudioList *) sharedInstance {
    if (gSharedInstance == nil) {
        gSharedInstance = [[AudioList alloc] init];
    }

    return gSharedInstance;
}

Now you can always access that instance with

[AudioList sharedInstance];

Cheers.

Answer 2

Create a singleton AudioManager class that handles all your music playback. When you navigate to that view controller, grab the shared instance of that AudioManager to do whatever you do in that view.

You don't want the view to persist as that would be bad separation of MVC.

Apple has some discussion of different design patterns and their objective-c implementations, including the singleton:

http://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaDesignPatterns/CocoaDesignPatterns.html#//apple_ref/doc/uid/TP40002974-CH6-SW6