Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSArrayM: 0x117540> was mutated while being enumerated

Im gettin the "Collection was mutates while beign enumerated" exception when my code is like this as follows:

NSString *poiStr = nil;
    int SuccessValue=0;
    NSMutableArray* poisArray=[[NSMutableArray alloc]init];
    for (id<MKAnnotation> annotation in mainMapView.annotations)
    {
        MKAnnotationView* anView = [mainMapView viewForAnnotation: annotation];
        if(anView)
        {

            POI* locationPOI = (POI*)[anView annotation];
            printf("\n Location poi shape groupId:%s=====%s",[locationPOI.shapeSpaceGroupId UTF8Stri开发者_JS百科ng],[poiStr UTF8String]);
            if((poiStr == nil) || ([poiStr isEqualToString:locationPOI.shapeSpaceGroupId]))
            {

                poiStr = locationPOI.shapeSpaceGroupId;
                [poisArray addObject:locationPOI];
                SuccessValue++;
            }
            printf("\n successValue:%d",SuccessValue);
            if(SuccessValue==2)
            {
                POI* poi=[poisArray objectAtIndex:0];
                [mainMapView removeAnnotation:poi];
                SuccessValue--;
            }

        }      

    }

Can anyone please suggest me what's the wrong in the code and how to solve the issues.

Thanks to all, Madan.

Basically you are modifying the list in the loop you are iterating over it. The line that causes the problem is:

[mainMapView removeAnnotation:poi];

as you are iterating over mainMapView.annotations. A possible solution is to accumulate the elements you want to delete in a different list and remove them after the loop.

Based on your code, a possible solution would be:

     NSString *poiStr = nil;
    int SuccessValue=0;
    NSMutableArray* poisArray=[[NSMutableArray alloc]init];
    NSMutableArray *to_delete = [[NSMutableArray alloc] init];
    for (id<MKAnnotation> annotation in mainMapView.annotations)
    {
        MKAnnotationView* anView = [mainMapView viewForAnnotation: annotation];
        if(anView)
        {

            POI* locationPOI = (POI*)[anView annotation];
            printf("\n Location poi shape groupId:%s=====%s",[locationPOI.shapeSpaceGroupId UTF8String],[poiStr UTF8String]);
            if((poiStr == nil) || ([poiStr isEqualToString:locationPOI.shapeSpaceGroupId]))
            {

                poiStr = locationPOI.shapeSpaceGroupId;
                [poisArray addObject:locationPOI];
                SuccessValue++;
            }
            printf("\n successValue:%d",SuccessValue);
            if(SuccessValue==2)
            {
                POI* poi=[poisArray objectAtIndex:0];
                //[mainMapView removeAnnotation:poi];
                [to_delete addObject:poi];
                SuccessValue--;
            }

        }      

    }
    for (id<MKAnnotation> annotation in to_delete)
           [mainMapView removeAnnotation:poi];

    [to_delete release];