Question

I’m having difficulties with UIAlertView delegation in class other than ViewController.
Everything is fine until user clicks the OK button – then app crashes with

Thread 1: EXC_BAD_ACCESS (code=2, address 0x8)

ViewController.h:

#import <UIKit/UIKit.h>
#import "DataModel.h"

@interface ViewController : UIViewController
@end

ViewController.m:

#import "ViewController.h"

@interface ViewController ()
@end

@implementation ViewController
- (void)viewDidLoad
{
    DataModel *dataModel = [[DataModel alloc] init];
    [dataModel ShowMeAlert];

    [super viewDidLoad];
}
@end

DataModel.h

#import <Foundation/Foundation.h>

@interface DataModel : NSObject <UIAlertViewDelegate>
- (void)ShowMeAlert;
@end

DataModel.m

#import "DataModel.h"

@implementation DataModel
- (void)ShowMeAlert;
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Info" message:@"View did load!" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
}

#pragma mark - UIAlertView protocol

- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
{
    NSLog(@"Index: %d", buttonIndex);
}

@end

• If code for showing alert and it’s delegation methods is in ViewController – works perfectly.
• When I remove UIAlertDelegation method ...didDismissWithButtonIndex... –
  works without delegation.
• When I set UIAlertView delegate to nil –
  works without delegation.

Any clues what’s wrong?

Answer 1

In this method:

- (void)viewDidLoad
{
  DataModel *dataModel = [[DataModel alloc] init];
  [dataModel ShowMeAlert];

  [super viewDidLoad];
}

you are allocating a DataModel local variable which will be deallocated by ARC at the end of the scope. Hence, when dismiss is executed, your delegate is not there anymore. The fix for this is to store your DataModel in a strong property of your view controller. This way it will not be deallocated. The you would do:

- (void)viewDidLoad
{
  self.dataModel = [[DataModel alloc] init];
  [self.dataModel ShowMeAlert];

  [super viewDidLoad];
}