ScrollViewDidScroll is called when the back button is pressed and the application crashes

Question

I got a weird result in my application. when I clicked the back button, scrollViewDidScroll always calls it, and this causes my application to crash.

The error will not happen if I do not scroll to the bottom (just load the view and then click the back button). but when I scroll to the bottom and then click the back button, it forces the shutdown. there is also no error if I scroll the bottom and then scroll back again to the middle of the table.

here is my code snippet.

    - (void)viewDidLoad
{
    [super viewDidLoad];
    self.title = @"Securities Instructions";


    currentPage = 1;
    isReloading = NO;
    totalPages = 1;
    isScrollingEnable = YES;
...... bla bla bla....
[self.tableView reloadData];
self.tableView.contentInset = UIEdgeInsetsMake(0, 0, 90, 0); //values passed are - top, left, bottom, right
}

-(void) viewWillDisappear:(BOOL)animated {
    if ([self.navigationController.viewControllers indexOfObject:self]==NSNotFound) {
        // back button was pressed.  We know this is true because self is no longer
        // in the navigation stack.
        NSLog(@"back button pressed");
        isScrollingEnable = NO;
    }
//    [super viewWillDisappear:animated];
}

- (void)scrollViewDidScroll:(UIScrollView *)aScrollView {
    NSLog(@"scroll view called");
    if (isScrollingEnable) {
        NSLog(@"scroll view get called: scroll enalbe");
        CGPoint offset = aScrollView.contentOffset;
        CGRect bounds = aScrollView.bounds;
        CGSize size = aScrollView.contentSize;
        UIEdgeInsets inset = aScrollView.contentInset;
        float y = offset.y + bounds.size.height - inset.bottom;
        float h = size.height;
        float reload_distance = 20;
        if(y > h + reload_distance) {
            if (isReloading==NO) {
                if (totalPages>1) {
                    if (currentPage<totalPages) {
                        NSLog(@"scroll view called");
                        currentPage++;
                        isReloading = YES;
                        [self getJsonOnLoad];
                    }
                }

            }
        }
    }
}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex{
    NSLog(@"index:%d",buttonIndex);
    if (buttonIndex==0) {
        if (totalPages!=9999) {
            [self.navigationController popViewControllerAnimated:YES];
        }
    }
}


- (void) getTotalPages{
    NSArray *detailArray = [self.jsonResult objectForKey:@"detail"];
    int detailCount = [detailArray count];

    //server tidak konsisten,parameter totalpages di menu ini tidak ada (menu lain ada) -_-!
    if (detailCount>=25) {
        if ([jsonHeader objectForKey:@"totalRows"]) {
            totalPages = [[jsonHeader objectForKey:@"totalRows"] floatValue]/25;
        }else{
            //buat unlimited
            totalPages = 9999;
        }
    }
}


//orientation handling
- (void)canRotate{}

- (void)viewWillAppear:(BOOL)animated
{
    [[NSNotificationCenter defaultCenter] addObserver:self  selector:@selector(orientationChanged:)  name:UIDeviceOrientationDidChangeNotification  object:nil];

}

-(void)viewDidDisappear:(BOOL)animated{
    [[NSNotificationCenter defaultCenter]removeObserver:self name:UIDeviceOrientationDidChangeNotification object:nil];
}



- (void)orientationChanged:(NSNotification *)notification{
    NSLog(@"orientation change...");
    [self adjustViewsForOrientation:[[UIDevice currentDevice] orientation]];
}

- (void) adjustViewsForOrientation:(UIInterfaceOrientation) orientation {

    NSLog(@"orientation:%d",orientation);

    if (orientation == UIInterfaceOrientationPortrait)

        //    if (orientation == UIInterfaceOrientationPortrait || orientation == UIInterfaceOrientationPortraitUpsideDown)

    {
        landscape = NO;
        //harus di tambahin ini karena parentnya uiviewcontroller bukan uitableviewcontroller jadi tidak otomatis
        self.tableView.frame = CGRectMake(self.tableView.frame.origin.x, self.tableView.frame.origin.y, 320, 480);
        [self.tableView layoutSubviews];

        [self.tableView setSeparatorStyle:UITableViewCellSeparatorStyleSingleLine];
        [self.tableView reloadData];

        //load the portrait view
        NSLog(@"portraid");
        [[UIApplication sharedApplication] setStatusBarHidden:NO];
        [self.navigationController.navigationBar setHidden:NO];


    }
    //    else if (orientation == UIInterfaceOrientationLandscapeLeft)

    if (orientation == UIInterfaceOrientationLandscapeLeft || orientation == UIInterfaceOrientationLandscapeRight)
    {
        landscape = YES;
        [self.tableView setSeparatorStyle:UITableViewCellSeparatorStyleSingleLine];

        //harus di tambahin ini karena parentnya uiviewcontroller bukan uitableviewcontroller jadi tidak otomatis
        self.tableView.frame = CGRectMake(self.tableView.frame.origin.x, self.tableView.frame.origin.y, 480, 320);
        [self.tableView layoutSubviews];



        [self.tableView reloadData];

        //load the landscape view
        NSLog(@"landscape");

        [[UIApplication sharedApplication] setStatusBarHidden:NO];
        [self.navigationController.navigationBar setHidden:NO];
    }
}

in .h

#import <UIKit/UIKit.h>

@interface SecuritiesInstructionsResultViewController : UIViewController<UITableViewDataSource, UITableViewDelegate>{

    NSDictionary *jsonHeader;

    //untuk paging
    NSInteger currentPage;
    Boolean *isReloading;
    NSInteger totalRows;
    float totalPages;

    BOOL landscape;

    BOOL isScrollingEnable;
}

@property (strong, nonatomic) IBOutlet UITableView *tableView;
//@property NSMutableArray *rowData;

@property NSMutableArray *dataAccount;

@property NSMutableArray *dataCashAmount;
@property NSMutableArray *dataCode;
@property NSMutableArray *dataDate;
@property NSMutableArray *dataExtRef;
@property NSMutableArray *dataInsType;
@property NSMutableArray *dataSecuritiesAmmount;
@property NSMutableArray *dataStatus;

@property NSString *dateFrom;
@property NSString *dateTo;

@property NSDictionary *jsonResult;

@property NSString *selectedAccount;
@property NSString *selectedSecurityCode;
@property NSString *selectedSecuritySecCodeType;
@property NSString *selectedSecurityType;
@property NSString *selectedCurrencyCode;
@property NSString *selectedStatus;
@property NSString *selectedDate;
@property NSString *selectedToDate;



@end

I have forbidden not to call the scrollviewdidscroll method when clicking the "Back" button when implementing viewWillDisappear, but this does not help. application still crash and error message.

- ?

Answer 1

UIScrollView (UITableView, UICollectionView ..) nil

Objective-C:

- (void)dealloc {
  [scrollView setDelegate:nil];
}

Swift:

deinit {
  scrollView.delegate = nil
}