Question

I am implementing a swipe to delete functionality in uitableview. I am able to achieve that, but now i wish to display a alert message to confirm delete. I have created the tableview programmatically.

ViewController.h

@interface ViewController : UIViewController<UITableViewDataSource,UITableViewDelegate>
{
    UITableView *tView;
    NSMutableArray *myArray;
    NSIndexPath *lastIndexPath;
}

@property(nonatomic,retain) UITableView *tView;
@property(nonatomic,retain) NSMutableArray *myArray;
@property(nonatomic,retain) NSIndexPath *lastIndexPath;

@end

ViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor=[UIColor lightGrayColor];

    myArray = [[NSMutableArray alloc] initWithObjects:@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"10", nil];

    // Do any additional setup after loading the view, typically from a nib.
    tView = [[UITableView alloc] initWithFrame:CGRectMake(30, 30, 700, 800) style:UITableViewStylePlain];
    tView.delegate=self;
    tView.dataSource=self;
    [self.view addSubview:tView];
    [tView release];
}

-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 100.0;
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [myArray count];
}

- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    // Return YES if you want the specified item to be editable.
    return YES;
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath 
{    
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Confirm Delete" message:@"Are you sure?" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"Delete", nil];

    [alert show];
    [alert release];
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        lastIndexPath = indexPath;
        NSLog(@"%@......%d",lastIndexPath,lastIndexPath.row);
    }
}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if(buttonIndex==0)
    {
        NSLog(@"cancel");
    }
    else {
        NSLog(@"delete");
        [myArray removeObjectAtIndex:lastIndexPath.row];    //memory error 
        [tView deleteRowsAtIndexPaths:[NSArray arrayWithObject:lastIndexPath] withRowAnimation:UITableViewRowAnimationFade];
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    //..do required thing and return cell
}

I get a memory error in the clickButtonAtIndex method for alert view. I think it is for the lastIndexPath, but the nslog() give the correct value in lastIndexPath.
What am i doing wrong?

Answer 1

I hate it when answers just say “You should’t do that”… So I’ll explain why you are getting an error and then hopefully appeal to your better judgement as to why you really ought not to do this (from a UI point of view).

You are getting an error because you assign a value you do not own (you have not retained it) to an ivar directly. You probably meant to say self.lastIndexPath.

What happens is that the alert view does not really appear until the next time through the run loop at which point indexPath has been autoreleased and you try to access it through a pointer.

Changing lastIndexPath = indexPath; to self.lastIndexPath = indexPath; should solve the memory issue. (Since you marked the property as retain, assuming you synthesized it and did not write your own handler, when you use the self. prefix the synthesized accessor will retain it for you).

(Incidentally this is why is not a bad idea to name your ivars differently from your properties (e.g. Apple uses <property_name>_, on my site I use m<Property_name> it makes it hard to make this sort of mistake).

OK… But back to why you should not do this….

You user has, at this point, made a recognizable gesture by swiping left and has then pressed a red button marked ‘delete’… And now you are going pop an alert and ask them to confirm? Really? OK, if you must…