How to make completely transparent navigation bar in iOS 7

Question

From this answer

[self.navigationController.navigationBar setBackgroundImage:[UIImage new]
                     forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.shadowImage = [UIImage new];
self.navigationController.navigationBar.translucent = YES;
self.navigationController.view.backgroundColor = [UIColor clearColor];
self.navigationController.navigationBar.backgroundColor = [UIColor clearColor];

Also, as suggested by Josh in the comments, to put the bar back to default:

[self.navigationController.navigationBar setBackgroundImage:nil
                     forBarMetrics:UIBarMetricsDefault];

For Swift3 and Swift4

self.navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
self.navigationController?.navigationBar.shadowImage = UIImage()
self.navigationController?.navigationBar.isTranslucent = true

For Swift2.2

 self.navigationController?.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: .Default)
 self.navigationController?.navigationBar.shadowImage = UIImage()
 self.navigationController?.navigationBar.translucent = true

For Objective-C

[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.shadowImage = [UIImage new];
self.navigationController.navigationBar.translucent = YES;

Self contained solution as an Objective-C Category:

UINavigationController+TransparentNavigationController.h

@interface UINavigationController (TransparentNavigationController)
- (void)presentTransparentNavigationBar;
- (void)hideTransparentNavigationBar;
@end

UINavigationController+TransparentNavigationController.m

#import "UINavigationController+TransparentNavigationController.h"

@implementation UINavigationController (TransparentNavigationController)

- (void)presentTransparentNavigationBar
{
  [self.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
  [self.navigationBar setTranslucent:YES];
  [self.navigationBar setShadowImage:[UIImage new]];
  [self setNavigationBarHidden:NO animated:YES];
}

- (void)hideTransparentNavigationBar
{
  [self setNavigationBarHidden:YES animated:NO];
  [self.navigationBar setBackgroundImage:[[UINavigationBar appearance] backgroundImageForBarMetrics:UIBarMetricsDefault] forBarMetrics:UIBarMetricsDefault];
  [self.navigationBar setTranslucent:[[UINavigationBar appearance] isTranslucent]];
  [self.navigationBar setShadowImage:[[UINavigationBar appearance] shadowImage]];
}

@end

Now, you can import the category in your UIViewController and call the methods on your navigation controller - for example:

#import "UINavigationController+TransparentNavigationController.h"

- (void)viewWillAppear:(BOOL)animated
{
  [super viewWillAppear:animated];
  [self.navigationController presentTransparentNavigationBar];
}

- (void)viewWillDisappear:(BOOL)animated
{
  [super viewWillDisappear:animated];
  [self.navigationController hideTransparentNavigationBar];
}

And a similar solution in Swift:

import Foundation
import UIKit

extension UINavigationController {

  public func presentTransparentNavigationBar() {
    navigationBar.setBackgroundImage(UIImage(), forBarMetrics:UIBarMetrics.Default)
    navigationBar.translucent = true
    navigationBar.shadowImage = UIImage()
    setNavigationBarHidden(false, animated:true)
  }

  public func hideTransparentNavigationBar() {
    setNavigationBarHidden(true, animated:false)
    navigationBar.setBackgroundImage(UINavigationBar.appearance().backgroundImageForBarMetrics(UIBarMetrics.Default), forBarMetrics:UIBarMetrics.Default)
    navigationBar.translucent = UINavigationBar.appearance().translucent
    navigationBar.shadowImage = UINavigationBar.appearance().shadowImage
  }
}

Alan forgot one line

self.navigationController.navigationBar.backgroundColor = [UIColor clearColor];

So I have:

[self.navigationController.navigationBar setTranslucent:YES];
self.navigationController.view.backgroundColor = [UIColor clearColor];
[self.navigationController.navigationBar setBackgroundImage:[[UIImage alloc] init] forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.shadowImage = [[UIImage alloc] init];
self.navigationController.navigationBar.backgroundColor = [UIColor clearColor];

@Zorayr's great answer revised to Swift 3 :

import Foundation
import UIKit

extension UINavigationController {

    public func presentTransparentNavigationBar() {
        navigationBar.setBackgroundImage(UIImage(), for:.default)
        navigationBar.isTranslucent = true
        navigationBar.shadowImage = UIImage()
        setNavigationBarHidden(false, animated:true)
    }

    public func hideTransparentNavigationBar() {
        setNavigationBarHidden(true, animated:false)
        navigationBar.setBackgroundImage(UINavigationBar.appearance().backgroundImage(for: UIBarMetrics.default), for:.default)
        navigationBar.isTranslucent = UINavigationBar.appearance().isTranslucent
        navigationBar.shadowImage = UINavigationBar.appearance().shadowImage
    }
}

Swift 4.2 and iOS 12

It turns out all you really need is the code below. It works perfectly when you put it into viewDidLoad().

// removes line at bottom of navigation bar
navigationController?.navigationBar.shadowImage = UIImage()

// makes navigation bar completely transparent
navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
navigationController?.navigationBar.isTranslucent = true