错误ARC'发布'不可用，错误变为“未使用表达式结果”

Question

I know that this is a similar question to the ARC deprecated code however, I have some old code from NIB days that I am upgrading to Storyboards and in doing so, the code revisions are causing me some issues.

In the code below:

- (void)audioSound {
    NSString *path = [[NSBundle mainBundle] pathForResource:@"sound-file" ofType:@"mp3"];
    if(theAudioSound)[theAudioSound release];
    theAudioSound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:NULL];
    theAudioSound.volume = 0.30;
    [theAudioSound play];
}

I get the ARC problem; After many attempts to find a solution I can only find the following advice.

   Delete the 'release'

If I do delete the release - depending on how I delete it - I get the following error messages.

from

if(theAudioSound)[theAudioSound release];

to

if(theAudioSound)[theAudioSound];

the Error is "Expected Identifier"

and from

if(theAudioSound)[theAudioSound];

to

if(theAudioSound)theAudioSound;

the Warning is "Expression Result Unused"

if I use the second of the two changes will it work? and if not; what would I need to do to change the code so that it does work?

Answer 1

// if(theAudioSound)[theAudioSound release];

You need to totally comment out that line for this to work.

Actually this is another way of writing following

        if(theAudioSound)
    {
        [theAudioSound release];
    }

If you simply delete release , that would generate a syntax error.

Answer 2

"Delete the 'release'" means you don't need to release it. So, you just remove the line or comment in. That's just all I think.

- (void)audioSound {
    NSString *path = [[NSBundle mainBundle] pathForResource:@"sound-file" ofType:@"mp3"];
    //if(theAudioSound)[theAudioSound release];
    theAudioSound = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:path] error:NULL];
    theAudioSound.volume = 0.30;
    [theAudioSound play];
}

Answer 3

Well, release actually releases( decreases the retain count) here, if any object has already has been created. But in ARC, you don't have to release it manually.

I suggest clearing the AVAudioPlayer instance in stead of release , and it will work. So the code will look like:

if(theAudioSound) {
    theAudioSound = nil;
}

OR

Simply delete or comment out the line if(theAudioSound)[theAudioSound release]; like:

// if(theAudioSound)[theAudioSound release];

And continue with the rest of codes. Hope this helps.