The app delegate must implement the window property if it wants to use a main storyboard file swift

问题

I have just developed an app, but when running in the simulator the debugger console says:

The app delegate must implement the window property if it wants to use a main storyboard file.

I have an app delegate file. What does the message mean, and how can I get my app working?

回答1:

Make sure you have the following property declaration in your AppDelegate class:

var window: UIWindow?

回答2:

If you run your project on earlier than iOS 13.0, in that case you will face the problem. Because of iOS 13 and later, app launch differently than earlier versions.

In iOS 13 and later, use UISceneDelegate objects to respond to life-cycle events in a scene-based app
In iOS 12 and earlier, use the UIApplicationDelegate object to respond to life-cycle events.

When you launch the app in iOS 12 and earlier then UIApplicationMain class expect a window property in your AppDelegate class as like SceneDelegate has. So your problem will be solved if you add the following line in your AppDelegate class.

var window: UIWindow?

For Objective-C

@property (strong, nonatomic) UIWindow *window;

You can find more here App's Life Cycle.

回答3:

Just in case anyone comes across this again and is programming in Objective-C make sure you have this line of code in your AppDelegate.h file:

@property (strong, nonatomic) UIWindow *window;

回答4:

I have received this error, when I created new project in XCode 11. I have not used SwiftUI. Here are the steps, I have considered to fix this.

Deleted Application Scene Manifest entry from Info.plist
Deleted SceneDelegate.swift file
Deleted all scene related methods in AppDelegate.swift class
added var window: UIWindow? property in AppDelegate.swift class

After these steps, I am able to run the app on version prior to iOS 13.

[EDIT]
Finally, your AppDelegate.swift file should look something like the following.

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

}

来源：https://stackoverflow.com/questions/29441682/the-app-delegate-must-implement-the-window-property-if-it-wants-to-use-a-main-st

标签

ios

iphone

xcode

swift

simulator