ios - prepareForSegue 首先返回 nil

Question

当我从单元格中转出时，我遇到了 fatal error :在展开可选值时意外发现 nil。

代码如下:

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    if indexPath.section == 1 {
        let listIngredients = recipeItem.ingredients[indexPath.row]
        selectedIngredient = listIngredients.ingredient
    }
    tableView.deselectRowAtIndexPath(indexPath, animated: false)
    performSegueWithIdentifier("showIngredientInRecipe", sender: self)


}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "showIngredientInRecipe" {
        let svc = segue.destinationViewController as! UINavigationController
        let destination = svc.topViewController as! IngredientDetailViewController

        destination.ingredientItem = selectedIngredient


        print("selectedIngredient \n \(selectedIngredient)")

    }

}

这是我从调试器中得到的:

        selectedIngredient
        nil

        selectedIngredient
        Optional(Ingredient {
            name = Rye Whiskey;
            inStock = 1;
            type = IngredientType {
                name = Spirit;
            };
        })

        fatal error: unexpectedly found nil while unwrapping an Optional value

如您所见，selectedIngredient 打印了两次。第一次为零，第二次为预期内容。如果我将 destination.ingredientItem = selectedIngredient 替换为 destination.ingredientItem = recipeItem.ingredients[0].ingredient segue 运行正常，没有错误。

Answer 1

您正在检查 indexPath 的部分是否为 1，如果不是，它仍将执行 segue。确保您的可选单元格位于第 1 节(或第 0 节？)并将您的 performSegueWithIdentifier("showIngredientInRecipe", sender: self) 调用移到 if 语句以使其更安全。