Flutter no windows have a root view controller, cannot save application state

Flutter: No Windows have a root view controller, cannot save application state

When encountering the error message “No Windows have a root view controller, cannot save application state” in Flutter, it typically means that there is an issue with the configuration or setup of your project.

To better understand this error, let’s go through some possible reasons and solutions:

1. Missing or incorrect root view controller: This error often occurs when the root view controller is not properly set in the AppDelegate (iOS) or MainActivity (Android) files.

Solution: Double-check the configuration in your platform-specific code and ensure that the root view controller is set correctly. Here are some examples of how it should be set:

iOS (AppDelegate.swift):

    
    // Inside `didFinishLaunchingWithOptions` method
    GeneratedPluginRegistrant.register(with: self)
    
    // Set root view controller
    self.window = UIWindow(frame: UIScreen.main.bounds)
    self.window?.rootViewController = FlutterViewController()
    self.window?.makeKeyAndVisible()
    
    

Android (MainActivity.kt):

    
    // Inside `onCreate` method
    GeneratedPluginRegistrant.registerWith(this)
    
    // Set root view controller
    val flutterView = FlutterMain.createView(this, lifecycle, "route")
    setContentView(flutterView)
    
    

2. Missing or incorrect Flutter engine initialization: Another possible cause is the absence of proper Flutter engine initialization in your code.

Solution: Make sure the Flutter engine is initialized before trying to set the root view controller. Here’s an example:

iOS (AppDelegate.swift):

    
    // Inside `didFinishLaunchingWithOptions` method
    FlutterEngineCache.getInstance().put("my_engine_id", MyFlutterEngine()) // Replace with your own engine id and implementation
    
    // Set root view controller
    self.window = UIWindow(frame: UIScreen.main.bounds)
    let flutterViewController = FlutterViewController(engine: FlutterEngineCache.sharedInstance().engine(withName: "my_engine_id"), nibName: nil, bundle: nil)
    self.window?.rootViewController = flutterViewController
    self.window?.makeKeyAndVisible()
    
    

Android (MainActivity.kt):

    
    // Inside `onCreate` method
    val flutterEngine = FlutterEngine(this)
    flutterEngine.dartExecutor.executeDartEntrypoint(FlutterMain.findAppBundlePath())
    FlutterEngineCache.getInstance().put("my_engine_id", flutterEngine) // Replace with your own engine id
    
    // Set root view controller
    val flutterView = FlutterMain.createView(this, lifecycle, "route")
    flutterView.attachToFlutterEngine(FlutterEngineCache.getInstance().engine("my_engine_id"))
    setContentView(flutterView)
    
    

3. Improper project structure or dependency issues: Sometimes, the error may be caused by a mismatch between Flutter and Dart versions or improper project structure.

Solution: Verify that your Flutter and Dart versions are compatible, and ensure that your project structure is correct. Try running “flutter clean” to clear any cached artifacts and rebuild your project to fix any dependency issues.

By following these troubleshooting steps and ensuring proper configuration, you should be able to resolve the “No Windows have a root view controller, cannot save application state” error in your Flutter project.