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I have an iOS app that I created with Xcode 4.0’s “Window-based Application” template. It worked fine back then and it was using the iOS 4.3 SDK. This is an app that simply puts the buttons, labels, etc. directly onto a window. No view controllers—no nothing.
But now that I’ve upgraded to Xcode 4.2 (and its iOS 5.0 SDK), and I run the app, this message gets logged to the console when the app launches in the simulator:
“Applications are expected to have a root view controller at the end of application launch”
To be sure, the app continues to work, but this rather bothersome log gets printed out on every launch.
Why is this happening? Why does iOS 5.0 prefer/request view controllers?
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A view controller acts as an intermediary between the views it manages and the data of your app. The methods and properties of the UIViewController class let you manage the visual presentation of your app. When you subclass UIViewController , you add any variables you need to manage your data in your subclass.
A view controller manages a single root view, which may itself contain any number of subviews. User interactions with that view hierarchy are handled by your view controller, which coordinates with other objects of your app as needed. Every app has at least one view controller whose content fills the main window.
A UIViewController is an object which manages the view hierarchy of the UIKit application. The UIViewController defines the shared behavior and properties for all types of ViewController that are used in the iOS application. The UIViewController class inherits the UIResponder class.
SwiftUI works seamlessly with the existing UI frameworks on all Apple platforms. For example, you can place UIKit views and view controllers inside SwiftUI views, and vice versa.
I don't know specifically why the message is logged, but integration between UIWindow and UIViewController has been increasing over the last several iterations of iOS. iOS 4 added a rootViewController property to UIWindow. The two classes work together to manage view rotation. Given the new capabilities that iOS 5 introduced to UIViewController (specifically, the ability to create your own container view controllers), it's clear that the relationship between the two classes will continue to evolve. As you've said, your app continues to function in iOS 5, so having a root view controller isn't a hard and fast requirement yet. Perhaps there are features planned for future iOS versions that will depend on having a view controller available.
I don’t have anything against them, and I will use them if iOS wants me to. I was just curious about the above behavior.
I'd interpret the logged message as a gentle but persistent nudge from Apple toward providing a root view controller. Most apps already use view controllers anyway, so this isn't a big change, but there are probably a number of apps out there that don't properly set the window's rootViewController property to their top-level view controller.
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You have just Connected your "view" with "File Owner".....just remove that connection and run your app.click your view and see the connections inspector area and remove that connection which I told..I dont know exactly what reason..but i had this issue and i cleared. May be you have used some tableview or some other views in it.So the app. needs a view controller to launch.If you remove that connection then it will run what you wrote in a code only...
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