How To Fix Error Use Of Unresolved Identifier ‘RootViewController’ In Xcode Swift Project

When I develop an iOS project in Xcode, I create a custom class RootViewController in RootViewController.swift file, this class is a subclass of UIViewController. But during the development process, when I use this custom class to create an object in another swift file ( for example SceneDelegate.swift ), I meet an error which said Use Of Unresolved Identifier ‘RootViewController’ In the Xcode Swift Project. This error message confused me a lot of times, and finally, I fix it, below are the steps and the method to fix it.

1. Fix Use Of Unresolved Identifier ‘RootViewController’ In Xcode Swift Project Error Steps.

  1. First, I create another new cocoa touch class in the project, the class name is TestViewController, it is saved in TestViewController.swift file. This is a whole new class, so I want to test whether the error exists when using this class.
  2. Then I write the below code in SceneDelegate.swift file to create an instance of the TestViewController class, and I found the error does not exist at all. So I think, this error is not because of the old RootViewController class, maybe because of the Xcode build cache.
    var testVC : TestViewController = TestViewController()
  3. Then I click Xcode Product —> Clean Build Folder menu item at Xcode top menu bar to clean the build folder. And then click Product —> Build menu item to build the project again. And now the above error disappear with the source code var rootVC : RootViewController = RootViewController() . So the error is because of the Xcode project build cache, what you need to do is just clean the build folder and build it again.
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