Objective-c 非弧 Object

Question

I'm managing an old Objective-c Project that still uses Non Arc , I noticed in Fabric Crashlytics for EXC_BAD_ACCESS KERN_INVALID_ADDRESS crash in the application.

This is the trace to the crash, I have this code line:

[view.label setText:[historyArray getStringForVideoArray]];

That call this function:

-(NSString*)getStringForVideoArray {
    NSString *str = nil;

    int seconds = 0;

    for (NSObject *video in self) {
        if (!video) {
            continue;
        }
        if ([video isKindOfClass:[VideoItem class]]) {
            VideoItem *tmp = (VideoItem*)video;
            seconds += tmp.seconds;
        }
    }

    if (seconds != 0) {
        int minutes = seconds / 60;
        if (minutes == 0 || minutes == 1) {
            minutes = 1;
            str = [NSString stringWithFormat:@"%d Min.",minutes];
        } else {
            str = [NSString stringWithFormat:@"%d Mins.",minutes];
        }
    } else {
        str = [NSString stringWithFormat:@""];
    }

    return str;
}

From what I noticed from Fabric Crashlytics , the crash is in this line:

if ([video isKindOfClass:[VideoItem class]]) {

The only thing I can think that can make this crash is that historyArray created in this method:

historyArray = [[NSMutableArray alloc] initWithArray:historyRep.historyArray];

And this is the definition of the array in the class:

@interface HistoryViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> {
    NSMutableArray *historyArray;
}

Any idea what can make this crash? It's not possible to change the project to ARC code, I'm really frustrated with not find this crash problem.

Edit

This is the three ways I insert items to the array:

1) When exchanging the position of an item in the array:

id object = [[[self.historyArray objectAtIndex:firstIndex] retain] autorelease];
[self.historyArray removeObjectAtIndex:firstIndex];
[self.historyArray insertObject:object atIndex:secondIndex];

2) Insert item from another class: [self.historyArray insertObject:video atIndex:0]; That created from:

if (self.videoItem)
    [self.videoItem release];
self.videoItem = [[VideoItem alloc] initWithVideoItem:item];

3) Init the array in the first time with:

NSArray *myRepository = [[NSUserDefaults standardUserDefaults] arrayForKey:@"kHistory"];
if(myRepository) { 
    for(NSData *data in myRepository) {
        VideoItem *video = (VideoItem*)[NSKeyedUnarchiver unarchiveObjectWithData:data];
        [self.historyArray addObject:video];
    }
}

Any suggestions what can make the problem?

Answer 1

As this is mutable array it can be cleaned during iteration that result in crash exactly at the line reported (because previous condition just for true, so even dangling pointer can pass, moreover it is senseless).

Here is possible solution

-(NSString*)getStringForVideoArray {
    NSString *str = nil;

    int seconds = 0;

    NSArray *tmp = [NSArray arrayWithArray:self]; // shallow copy - fast
    for (NSObject *video in tmp) {
        if ([video isKindOfClass:[VideoItem class]]) {
            VideoItem *tmp = (VideoItem*)video;
            seconds += tmp.seconds;
        }
    }

    ... // all below with no changes
}