从MasterViewController在DetailViewController中设置detailItem时出现奇怪的错误

Question

I started getting this error randomly (may be due to updating swift) but when I reach, didSet in detailItem, I call configureView. In configureView I check to see if detailItem is indeed set and then start assigning values to my outlets.

if let detail: Posting = self.detailItem {
        print("detail title is ")
        println(detail.title)

        // Title
        self.titleLabel.text = detail.title

However this crashes with output:

detail title is Skiing in Vail
fatal error: unexpectedly found nil while unwrapping an Optional value

The error is on the line:

self.titleLabel.text = detail.title

I don't understand why it is crashing when it is is clearly set... Note that this doesn't happen if I call configureView from within viewDidLoad.

This only happens when I call it from

 var detailItem: Posting? {
    didSet { self.configureView() }
}

Something I'm missing? Is this working asynchronously or something?

Answer 1

Referencing your comment on how to implement this, there are a few trains of thought. First, the reason you can modify it directly from your MasterVC is because the IBOutlet hasn't been instantiated in the DetailVC and thus isn't available to be modified yet.

One option, which I'd probably follow, is to have a helper variable on your detail view where you can place the value. Then viewWillAppear() you can take whatever's in the variable and set it as the label's text. Here's a tutorial on it, but to answer your specific quesiton please jump to the prepareForSegue method in this tutorial. It gives a good rundown of the whole process:

http://www.codingexplorer.com/segue-swift-view-controllers/

Let me know if this doesn't solve your problem.