Objective-C中的EXC_BAD_ACCESS错误

Question

I'm trying to write a simple iOS program that will notify when headphones are plugged/unplugged. I'm very new to Objective-C and iOS , and a lot of this code was written by somebody else and I'm now trying to adapt it so I'm having issues figuring out this problem. The code is here:

AppDelegate.m

#import "AppDelegate.h"

@implementation AppDelegate

static void onHeadsetChange(void *, AudioServicesPropertyID, UInt32, const void *);

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.headsetOnHandler = self.headsetOffHandler = ^{};
    NSLog(@"%lu", AudioSessionInitialize(NULL, NULL, NULL, NULL));
    NSLog(@"%lu", AudioSessionSetActive(true));
    NSLog(@"%lu", AudioSessionAddPropertyListener(kAudioSessionProperty_AudioRouteChange, &onHeadsetChange, (__bridge void *)self));
    return YES;
}

static void onHeadsetChange(void *inUserData, AudioSessionPropertyID inPropertyID, UInt32 inPropertyValueSize, const void *inPropertyValue) {
    if (inPropertyID != kAudioSessionProperty_AudioRouteChange) return;
    NSLog(@"The headset changed");
    AppDelegate *const delegate = (__bridge AppDelegate *)inUserData;

    const CFDictionaryRef routeChangeDictionary = inPropertyValue;
    const CFNumberRef routeChangeReasonRef = CFDictionaryGetValue(routeChangeDictionary, CFSTR(kAudioSession_AudioRouteChangeKey_Reason));
    SInt32 routeChangeReason;
    CFNumberGetValue(routeChangeReasonRef, kCFNumberSInt32Type, &routeChangeReason);
    switch (routeChangeReason) {
        case kAudioSessionRouteChangeReason_NewDeviceAvailable:
            //NSLog([delegate description]);
            [delegate headsetOnHandler];
            break;
        case kAudioSessionRouteChangeReason_OldDeviceUnavailable:
            [delegate headsetOffHandler];
            break;
        default:
            break;
    }
}
@end

ViewController.m

#import "ViewController.h"

@implementation ViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor redColor];
    AppDelegate *delegate = (AppDelegate *)([UIApplication sharedApplication].delegate);
    delegate.headsetOnHandler = ^{ self.view.backgroundColor = [UIColor greenColor];};
    delegate.headsetOffHandler = ^{ self.view.backgroundColor = [UIColor redColor];};
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

I'm getting the EXC_BAD_ACCESS error, code=1 at [delegate headsetOnHandler] and [delegate headsetOffHandler] . If I need to include the .h files for this to make sense, I will, and if there's anything else I'm missing please let me know.

EDIT: I've added in declarations that people thought should be added:

@property (readwrite, assign) void (^headsetOnHandler)(void);
@property (readwrite, assign) void (^headsetOffHandler)(void);

Answer 1

How is the headsetOnHandler and headsetOffHandler properties declared?

If it is assign or retain , that is likely the source of your problem. Since they are blocks, it needs to be copy (even, in certain cases, under ARC). If they are atomic and retain , then your getter will call, effectively, [[block retain] autorelease] in the getter, which would explain your crash.

A bit of a long shot.

• when you have a crash, always post the backtrace

• when you know the line of code the crash is on, always post the variable declarations of any variables on that line

Note that ARC will change this behavior a bit, automatically handling the blocks in some cases, but -- IIRC -- you would still need to copy them in this case.

Answer 2

Here's a good post on EXC_BAD_ACCESS by Ray Wenderlich.

http://www.raywenderlich.com/10209/my-app-crashed-now-what-part-1