iphone - CLLocation 导致 EXC_BAD_ACCESS

Question

此代码有时可以正常工作，但有时会因 EXC_BAD_ACCESS 错误而崩溃。

NSInteger compareDistance(id num1, id num2, void *context) 
{
    int rv;
    //cast parameters from general type
    CLLocation* location = (__bridge_transfer CLLocation *)context;
    Attraction* attr1 = num1;
    Attraction* attr2 = num2;

    //convert to CLLocation objects and calculate distance from user current
    CLLocation* locationAttr1 = 
    [[CLLocation alloc] initWithLatitude:attr1.latitude 
                               longitude:attr1.longitude];
    CLLocation* locationAttr2 = 
    [[CLLocation alloc] initWithLatitude:attr2.latitude 
                               longitude:attr2.longitude];
    CLLocationDistance distance1 = [locationAttr1 distanceFromLocation:location];
    CLLocationDistance distance2 = [locationAttr2 distanceFromLocation:location];

    //compare and rate
    if (distance1 < distance2)
        rv = NSOrderedAscending;
    else if (distance1 > distance2)
        rv = NSOrderedDescending;
    else
        rv = NSOrderedSame;

    return rv;
}

这是一个用于排序 NSMutableArray 的比较函数:

-(NSMutableArray *)getAttractionsByDistanceInCategory:(int)catID
{
    [self confirmAttractions];

    //set up array and context to prepare for sort
    NSMutableArray *attractionsToSort = [[NSMutableArray alloc] init];
    for (Attraction *a in attractions)
    {
        if ((catID < 0) || (catID >= 0 && a.category == catID))
            [attractionsToSort addObject:a];
    }

    CLLocation* currentLocation = 
        [[CLLocation alloc] initWithLatitude:usersLat longitude:usersLng];

    //conduct sort
    [attractionsToSort sortUsingFunction:compareDistance
                                 context:(__bridge_retained void *)currentLocation];

    return attractionsToSort;
}

嗯。您认为问题可能出在 ARC 上吗？我正在关注 __bridge_retained void * 业务。

提前感谢您的任何建议!

Answer 1

__bridge_transfer将所有权转移到目标对象，这可能不是您想在此处执行的操作，您不想要 context 的所有权，因为 ARC 会在它认为您已完成它而您不希望它这样做时尝试释放它。

基本上，您不想在任何地方转让所有权，所以只需使用 __bridge在这两种情况下，它应该都能正常工作。