How to set the full width of separator in UITableView

This worked for me on iOS 8.4 - 9.0 devices using Xcode 6.4 and Swift 1.2:

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    var cell = UITableViewCell()


    cell.preservesSuperviewLayoutMargins = false
    cell.separatorInset = UIEdgeInsetsZero
    cell.layoutMargins = UIEdgeInsetsZero

    return cell
}

Swift 5 Update:

cell.preservesSuperviewLayoutMargins = false
cell.separatorInset = UIEdgeInsets.zero
cell.layoutMargins = UIEdgeInsets.zero

In your UITableViewCell

Go to Attributes Inspector in your Interface Builder and simply change "15" to 0. Do this for all the cells you wish to change.

https://i.stack.imgur.com/A8rY1.png

You may need to add [cell setLayoutMargins:UIEdgeInsetsZero]; to your tableViewCell

I got the answer from this post: iOS 8 UITableView separator inset 0 not working

Just add this code on your UITableViewController

-(void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if ([cell respondsToSelector:@selector(setSeparatorInset:)]) {
        [cell setSeparatorInset:UIEdgeInsetsZero];
    }

    if ([cell respondsToSelector:@selector(setLayoutMargins:)]) {
        [cell setLayoutMargins:UIEdgeInsetsZero];
    }
}

-(void)viewDidLayoutSubviews
{
    [super viewDidLayoutSubviews];
    if ([self.tableView respondsToSelector:@selector(setSeparatorInset:)]) {
        [self.tableView setSeparatorInset:UIEdgeInsetsZero];
    }

    if ([self.tableView respondsToSelector:@selector(setLayoutMargins:)]) {
        [self.tableView setLayoutMargins:UIEdgeInsetsZero];
    }
}

for Swift 3 :

override func viewDidLoad() {
  super.viewDidLoad()

  tableView.separatorInset = .zero
  tableView.layoutMargins = .zero
}

Select your UITableViewCell Go to Atributes Inspector Go to Separator and change it to "custom Insets" Set left and / or right fields. (By default left: 15, right: 0)

Look how it works (using left: 100):

https://i.stack.imgur.com/zlC8T.png

Result:

https://i.stack.imgur.com/Uuv0N.png

I inherit from UITableViewController and needed additional to the two insets settings in willDisplayCell also to set preservesSuperviewLayoutMargins to false. In Swift it looks like this:

override func tableView(_tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {

    if cell.respondsToSelector("setSeparatorInset:") {
        cell.separatorInset = UIEdgeInsetsZero
    }
    if cell.respondsToSelector("setLayoutMargins:") {
        cell.layoutMargins = UIEdgeInsetsZero
    }
    if cell.respondsToSelector("setPreservesSuperviewLayoutMargins:") {
        cell.preservesSuperviewLayoutMargins = false
    }
}

The Separator Inset is by default 15 from left. Change Separator Inset option from auto to custom and set the inset to 0.

https://i.stack.imgur.com/l40TC.png

For Swift in iOS 9+

If using a custom UITableViewCell:

override var layoutMargins: UIEdgeInsets {
    get { return UIEdgeInsetsZero }
    set(newVal) {}
}

then for your UITableView in viewDidLoad:

self.tableView?.separatorInset = UIEdgeInsetsZero;
self.tableView?.layoutMargins = UIEdgeInsetsZero;

For people having issues with the iPad — this will get you in a state that is the same as the iPhone. You can then adjust the separatorInset as needed.

tableView.cellLayoutMarginsFollowReadableWidth = false

Use it in cellForRowAtIndexPath method, to configure cell's separator specs ,
it works perfect for iOS9.0+

 cell.separatorInset = UIEdgeInsetsZero;
 cell.layoutMargins = UIEdgeInsetsZero;
 cell.preservesSuperviewLayoutMargins = NO;

Tested for iOS 9.3 & Swift 2.2. Make sure to put the code in willDisplayCell which is called just before displaying the cell and not in cellForRowAtIndexPath where you create the cell only.

func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
    cell.separatorInset = UIEdgeInsetsZero
    cell.layoutMargins = UIEdgeInsetsZero
}

Add override to the function for UITableViewController, like so:

override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {

swift 5, Xcode 11 Update

place this inside viewDidLoad()

yourTableView.separatorInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)

for edge to edge separator just set the value of left and right to 0.

by the way change the "yourTableView" to your tableView Outlet name.

None of the above worked for me in Swift 2.2 and Xcode 7.3.1

Turned out to be the simplest solution of all. No code needed. Just change TableViewCell Layout Margins values in your UITableView inspector:

https://i.stack.imgur.com/0TC8z.png

For Swift 3 :

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: UITableViewCell.layoutMargins)) {
        cell.layoutMargins = UIEdgeInsets.zero
    }
    if cell.responds(to: #selector(setter: UITableViewCell.preservesSuperviewLayoutMargins)) {
        cell.preservesSuperviewLayoutMargins = false
    }
}

In viewDidLoad (tested iOS11 - swift 4.1)

try

tableView.separatorInset = UIEdgeInsetsMake(0, 0, 0, 0)

None of these solutions work on the iPad, but I have come up with a solution that covers both devices:

With reusable cells:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    ...[other code]...
    [cell setLayoutMargins:UIEdgeInsetsZero];
    [cell setSeparatorInset:UIEdgeInsetsZero];
    return cell;
}

With non reusable cells:

- (void)removeSeparatorInset:(UITableView*)tableView{
    NSArray *cells = [tableView visibleCells];
    for (UITableViewCell *cell in cells){
        [cell setLayoutMargins:UIEdgeInsetsZero];
        [cell setSeparatorInset:UIEdgeInsetsZero];
    }
}

-(void) viewDidLayoutSubviews{
   [super viewDidLayoutSubviews];
   [self removeSeparatorInset:self.tableView];
}

Just to expand on this approach:

@property(nonatomic) UIEdgeInsets separatorInset;
@property(nonatomic) UIEdgeInsets layoutMargins;

Both properties can be used by UITableView & UITableViewCell. The latter is, in fact, a property of UIView, which is a parent class of both UITableView & UITableViewCell.