iOS 9 UITableView separators insets (significant left margin)

Okay, I have found out the solution. The only thing required for that is to set on the presenting instance of UITableView that flag cellLayoutMarginsFollowReadableWidth

myTableView.cellLayoutMarginsFollowReadableWidth = NO;

I wanted to find some reference in the documentation but it looks like it is not ready yet, only mentioned on diff page.

As the flag was introduced in iOS 9 for the backward compatibility you should add a check before trying to set it:

if([myTableView respondsToSelector:@selector(setCellLayoutMarginsFollowReadableWidth:)])
{
    myTableView.cellLayoutMarginsFollowReadableWidth = NO;
}

For Swift 2.0 you can use #available to check iOS version.

if #available(iOS 9, *) {
    myTableView.cellLayoutMarginsFollowReadableWidth = false
}

Moreover you need to compile it with Xcode 7 or above.

EDIT

Please keep in mind that this is the only required fix if your separators looked "fine" up to iOS 8, otherwise you need to change a bit more. You can find info how to do this already on SO.

If you want to do it in interface builder. The default separator inset is Automatic. Change it to custom by selecting the dropdown.

Swift 2.2 iOS 9.3

In viewDidLoad

tableView.cellLayoutMarginsFollowReadableWidth = false

In UITableViewDelegates

func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
    if cell.respondsToSelector(Selector("setSeparatorInset:")){
        cell.separatorInset = UIEdgeInsetsZero
    }
    if cell.respondsToSelector(Selector("setPreservesSuperviewLayoutMargins:")) {
        cell.preservesSuperviewLayoutMargins = false
    }
    if cell.respondsToSelector(Selector("setLayoutMargins:")){
        cell.layoutMargins = UIEdgeInsetsZero
    }
}

Perfect Solution upto iOS 9

In viewDidLoad

- (void)viewDidLoad {
    [super viewDidLoad];
    //Required for iOS 9
    if ([[[UIDevice currentDevice]systemVersion]floatValue] >= 9.0) {
        self.testTableView.cellLayoutMarginsFollowReadableWidth = NO;
    }
}

In TableViewDelegate methods add following code:

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {

    // Remove seperator inset
    if ([cell respondsToSelector:@selector(setSeparatorInset:)]) {
        [cell setSeparatorInset:UIEdgeInsetsZero];
    }

    // Prevent the cell from inheriting the Table View's margin settings
    if ([cell respondsToSelector:@selector(setPreservesSuperviewLayoutMargins:)]) {
        [cell setPreservesSuperviewLayoutMargins:NO];
    }

    // Explictly set your cell's layout margins
    if ([cell respondsToSelector:@selector(setLayoutMargins:)]) {
        [cell setLayoutMargins:UIEdgeInsetsZero];
    }
}

Swift 3.0 / 4.0

tableView.cellLayoutMarginsFollowReadableWidth = false

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    if cell.responds(to: #selector(setter: UITableViewCell.separatorInset)) {
        cell.separatorInset = UIEdgeInsets.zero
    }
    if cell.responds(to: #selector(setter: UIView.preservesSuperviewLayoutMargins)) {
        cell.preservesSuperviewLayoutMargins = false
    }
    if cell.responds(to: #selector(setter: UIView.layoutMargins)) {
        cell.layoutMargins = UIEdgeInsets.zero
    }
}