How to adjust space between two UIBarButtonItem in rightBarButtonItems

My solution is using a custom view for right bar buttons. Create a horizontal stackview with equal spacing and add any number of buttons as subview.

Sample code:

func addRightBarButtonItems()
{
    let btnSearch = UIButton.init(type: .custom)
    btnSearch.setImage(UIImage(systemName: "magnifyingglass"), for: .normal)
    btnSearch.addTarget(self, action: #selector(MyPageContainerViewController.searchButtonPressed), for: .touchUpInside)
    
    let btnEdit = UIButton.init(type: .custom)
    btnEdit.setImage(UIImage(systemName: "pencil"), for: .normal)
    btnEdit.addTarget(self, action: #selector(MyPageContainerViewController.editButtonPressed), for: .touchUpInside)
    
    let stackview = UIStackView.init(arrangedSubviews: [btnEdit, btnSearch])
    stackview.distribution = .equalSpacing
    stackview.axis = .horizontal
    stackview.alignment = .center
    stackview.spacing = 8
    
    let rightBarButton = UIBarButtonItem(customView: stackview)
    self.navigationItem.rightBarButtonItem = rightBarButton
}

Updated at Jul 2015

A better way to do this is to use storyboard (tested in Xcode 6.4). First, add a UINavigationItem; secondly, add a Bar Button Item; thirdly, add a view to the Bar Button Item you just created in step 2; fourthly, add as many buttons as you wish into that view you just dragged in; lastly, adjust the space with your mouse and constraints.

Related Questions

Can't assign multiple Buttons to UINavigationItem when using Storyboard with iOS 5

How to add buttons to navigation controller visible after segueing?

---

Old Answer (Only acceptable for small insets)

Use imageInsets property:

leftButton.imageInsets = UIEdgeInsetsMake(0.0, 0.0, 0, -15);
rightButton.imageInsets = UIEdgeInsetsMake(0.0, -15, 0, 0);

for three or more buttons, the middle one(s) get both insets:

leftButton.imageInsets = UIEdgeInsetsMake(0.0, 0.0, 0, -15);
middleButton.imageInsets = UIEdgeInsetsMake(0.0, -15, 0, -15);
rightButton.imageInsets = UIEdgeInsetsMake(0.0, -15, 0, 0);

For the right side buttons, be careful: the FIRST button in the item array is the RIGHT one:

rightButton.imageInsets = UIEdgeInsetsMake(0.0, -15, 0, 0);
middleButton.imageInsets = UIEdgeInsetsMake(0.0, -15, 0, -15);
leftButton.imageInsets = UIEdgeInsetsMake(0.0, 0.0, 0, -15);

IMPORTANT: Split the inset between the two neighbors; if apply the entire inset to one edge, it will become obvious that the buttons are overlapping in the "blank" space - one button gets all of the "gap" touches. Even when "split" the adjustment like this, at -40 on both edges, the tap will definitely go to wrong button sometimes. -15 or -20 is the most to consider using with this technique.

By applying this method, the button could even be moved around in four directions.

Swift 5

In your AppDelegate add this code:

let stackViewAppearance = UIStackView.appearance(whenContainedInInstancesOf: [UINavigationBar.self])
stackViewAppearance.spacing = -10

This will work with no additional code in more recent SDK versions as UIBarButtonItems are already contained in a horizontal UIStackView