ios - UISplitViewController 扩展给应用带来了麻烦

Question

我有一个简单的 UISplitViewController 扩展:

extension UISplitViewController {

    var masterViewController: UIViewController? {
        return (viewControllers.first as? UINavigationController)?.topViewController
    }
}

在一些 UIViewController 中，我确实将模态转场连接到我的 UISplitViewController。当执行 segue 时，我会像这样准备我的 destinationViewController:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

    if let searchResultsViewController = (segue.destinationViewController as? UISplitViewController)?.masterViewController as? SearchResultsViewController {
        searchResultsViewController.mode = mode
    }
}

由于错误，它不起作用:

*** Terminating app due to uncaught exception 'NSGenericException', reason: 'The content view controller argument must be the root of its associated view controller hierarchy.'

但是，当我删除 UISplitViewController 的扩展并准备 destinationViewController 时，如下所示:

if let searchResultsViewController = ((segue.destinationViewController as? UISplitViewController)?.viewControllers.first as? UINavigationController)?.topViewController as? SearchResultsViewController {
    //prepare controller
}

它有效

What is the reason that it is not working in first case?

Answer 1

尝试将计算变量的名称从 masterViewController 更改为其他名称。您似乎正在覆盖 UISplitViewController 的内部属性。

这有效，并且在 UISplitViewController 的设置过程中不会被调用。

var masterVC: UIViewController? {
    return (viewControllers.first as? UINavigationController)?.topViewController
}

这由 SDK 中的某些内容调用并导致崩溃。

var masterViewController: UIViewController? {
    return (viewControllers.first as? UINavigationController)?.topViewController
}