# Hot Reloading a SceneDelegate in Swift

I told you about [Hot Reloading a SwiftUI App](https://blog.eidinger.info/hot-reloading-a-swiftui-app) in my previous blog post.

In this blog post, I will tell you how to inject code that is not bound to a UI representation. Example: you need to change code in your scene delegate when testing the handling of custom URLs in a UIKit-based app.

You need the same tooling:

- `Inject`, a Swift Package created by Krzysztof Zabłocki
- `InjectionIII`, a macOS application for the heavy lifting (i.e. watching for modified source code and interposing the new function as if it had been compiled into the SwiftUI app)

I assume you made the necessary configurations in the Build Settings of your App
(`-Xlinker -interposable`) and that you run the `InjectIII.app` on your Mac.

The critical difference is that we don't use `Inject.ViewControllerHost(...)` or `Inject.ViewHost(...)`. Instead we call the lazy property `Inject.load` in the AppDelegate so that `InjectIII.app` will watch for file changes right from the application start.

```Swift
import UIKit
import Inject

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        Inject.load // connects running iOS simulator with InjectIII.app
        return true
    }
    // ...
}
```

That's it !

In my video, I also prove that changes to `SceneDelegate.swift` will be injected and eventually executed when called by the iOS lifecycle handling.

%[https://youtu.be/JIfip0s3KX8]

For my video I [registered a URL scheme](https://developer.apple.com/documentation/xcode/defining-a-custom-url-scheme-for-your-app) in the `Info.plist`.

I added the following function to the `SceneDelegate` class *before* running the app.

```Swift
func scene(_ scene: UIScene, openURLContexts URLContexts: Set<UIOpenURLContext>) {
    for context in URLContexts {
        print("url: \(context.url.absoluteURL)")
        print("scheme: \(String(describing: context.url.scheme))")
        print("host: \(String(describing: context.url.host))")
        print("path: \(context.url.path)")
        print("components: \(context.url.pathComponents)")
    }
}
```

Once the app starts running in the iOS simulator, I change the implementation of `scene(_:openURLContexts:)`

Using the terminal command `xcrun simctl openurl booted <myCustomURLScheme>`, I invoke a custom URL in the running iOS simulator, and I witness that the injected code gets executed.