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How to debug your view hierarchy using recursiveDescription

Paul Hudson       @twostraws

Xcode has a built-in view debugger that captures all the views inside the currently running app, then shows them in 3D. You can then filter that list based on classes, subclasses, and contents of your views, or right-click on a view and choose Focus On UIView to view just part of your view hierarchy.

But while this view debugger is great to have around, it can be clumsy to use in two situations: trying to compare multiple view frames at the same time, and trying to compare one view’s frames across several runs of your app.

Fortunately, UIView has a hidden method called recursiveDescription() that prints out an ASCII rendering of your view hierarchy – all the views, their children, their positions, some of their content, whether they are responding to user input, and so on.

This method is specifically there for debugging purposes – it’s not something you would ever want to call in production – but because it uses plain text in Xcode’s console, it can be easier to compare one view’s position against another, or perhaps against itself if you’re looking at different runs of your app.

Swift doesn’t make it easy to call hidden methods; the easiest way I’ve found is to run this from the LLDB prompt in Xcode:

po yourView.value(forKey: "recursiveDescription")!

So, place a breakpoint in your code wherever you’d like to inspect your view hierarchy, and try it out!

 

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About the author

Paul Hudson is the creator of Hacking with Swift, the most comprehensive series of Swift books in the world. He's also the editor of Swift Developer News, the maintainer of the Swift Knowledge Base, and Mario Kart world champion. OK, so that last part isn't true. If you're curious you can learn more here.

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