How to call a function from an extension to UIViewController in Swift

Question

I am trying to make my Navigation bar transparent. It works when i create the function within the same ViewController however i want to reuse it in many other ViewControllers so i decided to use an extension extending the UINavigationController. When i try calling the function into ViewDidLoad, it doesn't work.

import UIKit

class StudentsViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.navigationController?.makeNavigationBarTransparent()   
    } 
}

Here is my extension

import UIKit

extension UINavigationController {
    func makeNavigationBarTransparent() {
        navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
        navigationController?.navigationBar.shadowImage = UIImage()
    }
}

@AshleyMills, It was just a suggestion. He also said that in other view controller doesn't work so... — Mahendra, May 29 '18 at 12:35

score 3 · Answer 1 · answered May 29 '18 at 12:32

Since you decided to write the extension for navigation controller, you must write it from its prespective:

import UIKit

extension UINavigationController {
    func makeNavigationBarTransparent() {
        self.navigationBar.setBackgroundImage(UIImage(), for: .default)
        self.navigationBar.shadowImage = UIImage()
    }
}

score 3 · Accepted Answer · answered May 29 '18 at 12:32

3

You don't need the on the navigationController?.

extension UINavigationController {
    func makeNavigationBarTransparent() {
        navigationBar.setBackgroundImage(UIImage(), for: .default)
        navigationBar.shadowImage = UIImage()
    }
}

answered May 29 '18 at 12:32

Ashley Mills

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score 1 · Answer 3 · answered May 29 '18 at 12:37

1

It's because your viewController isn't placed in your navigation stack yet. If your vc isn't placed in navigation stack then self.navigationController will returns nil.

Try to move your makeNavigationBarTransparent() call to viewWillAppear method.

answered May 29 '18 at 12:37

U. Benlice

901
9
14

How to call a function from an extension to UIViewController in Swift

3 Answers3