IB Designables for storyboard UITableViewCell: Failed to render and update auto layout status for CountdownViewController The agent crashed

Question

Seems like I am using @IBDesignbale wrong, but why?

I want to use a combination of IBDesignable and prepareForInterfaceBuilder to inject some data into my MyTableViewCell so it can display some dummy data(in this sample project, just set the dummyView.backgroundColor = .red ) in my storyboard.

My current setup:

1, I guess the usual setup for a tableview using storyboard. TableView inside a view and dragged a UITableViewCell into the tableview.

2, marked my MyTableViewCell @IBDesignable

3, override prepareForInterfaceBuilder inside the MyTableViewCell setting the dummyView backgroundColor

error:

Main.storyboard: error: IB Designables: Failed to render and update auto layout status for ViewController (BYZ-38-t0r): The agent crashed

Answer 1

This is happening because your dummyView is an IBOutlet and is implicitly unwrapped. prepareForInterfaceBuilder will be called before dummyView is initialized. You can prevent a crash by changing your code to dummyView?.backgroundColor = .red but then nothing will be rendered because dummyView == nil.

It doesn't make a ton of sense to mix IBDesignable with IBOutlet. In general, IBDesignable is meant to make run time layout and drawing visible at design time. But IBOutlets are necessarily already visible at design time. This might however be desirable in a xib. For a discussion of that see here and here.