Flawed for loop!

I have a for loop which for some reason wont allow me to delete all objects in an array, only a few.

What am I doing wrong?

- (void)deleteAllObjects {
    AppDelegate *appDel = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSLog(@"Before: %d", [histArray count]);
    for (int i = 0; i < [histArray count]; i++) {
        History *h = (History *)[histArray objectAtIndex:i开发者_StackOverflow社区];
        [[appDel managedObjectContext] deleteObject:h];
        [histArray removeObject:h];
        [appDel saveContext];
        NSLog(@"During: %d", [histArray count]);
        [self fetchUpdates];
    }
    NSLog(@"After: %d", [histArray count]);
}

You're shortening the array as you loop over it, by calling [histArray removeObject:h]. Since you're removing every object in histArray, why not just wait until after the loop completes and then remove everything at once with [histArray removeAllObjects]?

Another solution is to loop over the array from the end to the beginning.

Don't modify an array while you're iterating over its contents. This is particularly important if you're using fast iteration, but it can be a problem even when you're not, as it is here. The issue is that you're changing the positions of the objects by removing objects.

If you must do this, you can:

• Remove the objects starting from the end of the array and working toward the start, or
• Don't increase the index. If you remove the object at the beginning of the array for [array count] times, you'll have removed all the objects.

But again, don't change the array if you're using fast iteration or if you're using an enumerator.

You are deleting from "histArray" and also you are running your loop on the same array. I think need to reset the indexes after each iteration. Remove the statement "[histArray removeObject:h];" from your loop and at the end of your loop call removeAll function on your array to clear it. It will solve the problem,

Here is the modified code,

- (void)deleteAllObjects {
    AppDelegate *appDel = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSLog(@"Before: %d", [histArray count]);
    for (int i = 0; i < [histArray count]; i++) {
        History *h = (History *)[histArray objectAtIndex:i];
        [[appDel managedObjectContext] deleteObject:h];
        [appDel saveContext];
        NSLog(@"During: %d", [histArray count]);
        [self fetchUpdates];
    }
    [histArray removeAllObjects];
    NSLog(@"After: %d", [histArray count]);
}

Try changing:

for (int i = 0; i < [histArray count]; i++) {

into:

for (int i = [histArray count] - 1; i >= 0; i--) {

The reason your current loop isn't working is because, when you delete index 0, indexes 1 through 50 don't stay where they are, they shuffle up so that 1 becomes 0, 2 becomes 1 and so on.

So the next time through your loop when you delete index 1, you're leaving the new item at index 0 in there.

By doing the loop backwards, you remove this shuffling and all indexes should be deleted.