How to draw a transparent UIToolbar or UINavigationBar in iOS7

Question

I would like an entirely transparent UIToolbar and/or UINavigationBar. I have tried the various incantations suggested for pre- and post-iOS 5 but

Answer 1

Swift 3 (iOS 10)

Transparent UIToolbar

self.toolbar.setBackgroundImage(UIImage(),
                                forToolbarPosition: .any,
                                barMetrics: .default)
self.toolbar.setShadowImage(UIImage(), forToolbarPosition: .any)

Transparent UINavigationBar

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

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Swift < 3

Transparent UIToolbar

self.toolbar.setBackgroundImage(UIImage(),
                                forToolbarPosition: UIBarPosition.Any,
                                barMetrics: UIBarMetrics.Default)
self.toolbar.setShadowImage(UIImage(),
                            forToolbarPosition: UIBarPosition.Any)

Transparent UINavigationBar

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

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Objective-C

Transparent UIToolbar

[self.toolbar setBackgroundImage:[UIImage new]
              forToolbarPosition:UIBarPositionAny
                      barMetrics:UIBarMetricsDefault];
[self.toolbar setShadowImage:[UIImage new]
          forToolbarPosition:UIBarPositionAny];

---

Transparent UINavigationBar

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

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Discussion

Setting translucent to YES on the navigation bar does the trick, due to a behavior discussed in the UINavigationBar documentation. I'll report here the relevant fragment:

If you set this property to YES on a navigation bar with an opaque custom background image, the navigation bar will apply a system opacity less than 1.0 to the image.

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Final result