I assume you have gone through an earlier article related to this topic called:
How to add four or more navigation bar buttons in your iOS App XCode Project
Background:
Now you will be wondering how you can add a fourth button to the navigation bar of your iOS app with a custom image through code
Here is the solution:
// add our custom image button as the nav bar's custom right view
UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"Email"]
style:UIBarButtonItemStyleBordered target:self action:@selector(action:)];
self.navigationItem.rightBarButtonItem = addButton;
Note: change your desired image name at second line ‘Email’
Hope it helps,
Thanks & Regards
Mandar Apte