How to make image on unbutton persist until its not changed by the user .?

I am working on UIButton as a check box, when I press button than checkbox selected image is appear and when press again checkbox unselected image is appear. if I press button image is appear, but it again disappear when I come back to that view again.

- (void)viewDidLoad {
     [super viewDidLoad];

     _car.delegate = self;
     _car.keyboardType = UIKeyboardTypeNumberPad;


     [_PreCheck setBackgroundImage:[UIImage imageNamed:@"checkbx_unchecked@2x.png"] forState:UIControlStateNormal];
     [_PreCheck setBackgroundImage:[UIImage imageNamed:@"checkbx@2x.png"] forState:UIControlStateSelected];
     [_PreCheck addTarget:self action:@selector(checkboxSelected:) forControlEvents:UIControlEventTouchUpInside];
}

- (void)didReceiveMemoryWarning {
     [super didReceiveMemoryWarning];
}

-(void)checkboxSelected:(id)sender
{
    if ((checkBoxSelected = !checkBoxSelected)) {
        [_PreCheck setSelected:checkBoxSelected];
        NSLog(@"selected");
        NSString *selected = @"selected";
        NSUserDefaults *select = [NSUserDefaults standardUserDefaults];
        [select setObject:selected forKey:@"checkboxselected"];
        [select synchronize];
    }
    else
    {
        NSLog(@"not selected");
        [_PreCheck setSelected:notselected];
    }
}