懒惰的TableView图像加载Malloc错误

Question

I am attempting to lazy load images onto my tableview, but I am getting a double free malloc error when I attempt to insert one specific image into my images array.

This is the error: "Flags(8079,0xa0258540) malloc: * error for object 0x6a51b40: double free * set a breakpoint in malloc_error_break to debug".

Here is my code:

#import "ViewController.h"
#import "ASync.h"

@implementation ViewController
@synthesize tableView;
@synthesize countryNamesArray;
@synthesize receivedData; 
@synthesize flagImage;
@synthesize flagImagesArray;
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle
-(void)issueRequest:(NSString *)fullCountryImageURL{

    NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:fullCountryImageURL]
                                              cachePolicy:NSURLRequestUseProtocolCachePolicy
                                          timeoutInterval:60.0];
    // create the connection with the request
    // and start loading the data
    NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
    if (theConnection) {
        // Create the NSMutableData to hold the received data.
        // receivedData is an instance variable declared elsewhere.
        receivedData = [NSMutableData data];                                    
    } 
    else {
        // Inform the user that the connection failed.
    }
}

- (void)viewDidLoad
{   
    flagImagesArray = [[NSMutableArray alloc]init];
    for(int x=0; x<16; x++){
        [flagImagesArray insertObject:[UIImage imageNamed: @"jollyroger_poisonflag.jpg"] atIndex:x];

    }
    countryNamesArray=[[NSArray alloc] initWithObjects:@"India",@"USA",@"Antarctica",@"Brazil",@"Canada",@"China",@"France",@"Germany",@"Italy",@"Japan",@"Kenya",@"Malaysia",@"Mexico",@"South Africa",@"United Kingdom",@"Vietnam",nil];


    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
    } else {
        return YES;
    }
}

-(NSInteger)tableView:(UITableView *)tableview numberOfRowsInSection:(NSInteger)section{
    return 16;
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // This method is called when the server has determined that it
    // has enough information to create the NSURLResponse.

    // It can be called multiple times, for example in the case of a
    // redirect, so each time we reset the data.

    // receivedData is an instance variable declared elsewhere.
    [receivedData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // Append the new data to receivedData.
    // receivedData is an instance variable declared elsewhere.
    [receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connectiondidFailWithError:(NSError *)error
{
    // release the connection, and the data object
    // receivedData is declared as a method instance elsewhere


    // inform the user
    NSLog(@"Connection failed! Error - %@ %@",
          [error localizedDescription],
          [[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // do something with the data
    // receivedData is declared as a method instance elsewhere
    NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]);
    flagImage = [UIImage imageWithData: receivedData];
    if([receivedData length]==19935){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==0)
                [flagImagesArray replaceObjectAtIndex:0 withObject:flagImage];
        }
    }
    else if([receivedData length]==9280){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==1)
                [flagImagesArray replaceObjectAtIndex:1 withObject:flagImage];
        }
    }
    else if([receivedData length]==9567){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==2)
                [flagImagesArray replaceObjectAtIndex:2 withObject:flagImage];
        }
    }
    else if([receivedData length]==12152){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==3)
                [flagImagesArray replaceObjectAtIndex:3 withObject:flagImage];
        }
    }
    else if([receivedData length]==10903){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==4)
                [flagImagesArray replaceObjectAtIndex:4 withObject:flagImage];
        }
    }
    else if([receivedData length]==11298){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==5)
                [flagImagesArray replaceObjectAtIndex:5 withObject:flagImage];
        }
    }
    else if([receivedData length]==8682){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==6)
                [flagImagesArray replaceObjectAtIndex:6 withObject:flagImage];
        }
    }
    else if([receivedData length]==6865){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==7)
                [flagImagesArray replaceObjectAtIndex:7 withObject:flagImage];
        }
    }
    else if([receivedData length]==10567){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==8)
                [flagImagesArray replaceObjectAtIndex:8 withObject:flagImage];
        }
    }
    else if([receivedData length]==9423){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==9)
                [flagImagesArray replaceObjectAtIndex:9 withObject:flagImage];
        }
    }
    else if([receivedData length]==820){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==10)
                **[flagImagesArray replaceObjectAtIndex:10 withObject:flagImage];**
        }
    }
    else if([receivedData length]==12238){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==11)
                [flagImagesArray replaceObjectAtIndex:11 withObject:flagImage];
        }
    }
    else if([receivedData length]==5980){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==12)
                [flagImagesArray replaceObjectAtIndex:12 withObject:flagImage];
        }
    }
    else if([receivedData length]==10562){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==13)
                [flagImagesArray replaceObjectAtIndex:13 withObject:flagImage];
        }
    }
    else if([receivedData length]==9690){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==14)
                [flagImagesArray replaceObjectAtIndex:14 withObject:flagImage];
        }
    }
    else if([receivedData length]==11590){
        for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
            if(indexPath.row==15)
                [flagImagesArray replaceObjectAtIndex:15 withObject:flagImage];
        }
    }


    [tableView reloadData];
}



-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *cellIdentifier = @"countryCell";
    static int numberOfRequests=0;
    UITableViewCell *cell=(UITableViewCell *) [self.tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (cell==nil){
        cell=[[UITableViewCell alloc] initWithStyle: UITableViewCellStyleSubtitle reuseIdentifier:cellIdentifier];
    }

    // Create the request.

    NSString *flagImageURLPartOne = @"http://www.imageslink/";
    NSString *countryNumber = [NSString stringWithFormat:@"%i", indexPath.row];
    NSString *flagImageURLPartTwo = @".png";
    NSString *fullCountryImageURL = [NSString stringWithFormat:@"%@%@%@", flagImageURLPartOne, countryNumber, flagImageURLPartTwo];
    [self issueRequest:fullCountryImageURL];
    numberOfRequests++;



    cell.imageView.image=[flagImagesArray objectAtIndex:indexPath.row];
    cell.textLabel.text= [countryNamesArray objectAtIndex:indexPath.row];

    return cell;
}

-(void) tableView:(UITableView *) tableview didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
}


@end

The line that is throwing the error is bolded - it is below the code line: "[flagImagesArray replaceObjectAtIndex:10 withObject:flagImage];". When I comment this line out, all the other images load fine. Anyone have any ideas as to what the problem is?

Answer 1

Go to breakpoints tab, and on the lower left corner click the add button and select "Add Exception Breakpoint" and click done.

Run your code again, and you will find exactly when and where you are getting the crash, as well as all the debug information

Answer 2

Only for completion's sake.

The problem is most probably with the image. The image might be corrupted. Using break points inside the 820 bracket will tell us where the error has occurred.

In cases like these. I always suggest doing a count on the data just to be sure about the data transferred from the server.

And John solved the problem. The problem was

I had one link that was pulling in a "Page Not Found" rather than an image.