Question

当我离开牢房时，我得到fatal error: unexpectedly found nil while unwrapping an Optional value。

以下是代码：

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)")

    }

}

以下是我从调试器获得的内容：

        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打印两次。首先是nil，第二次是预期的内容。如果我用destination.ingredientItem = selectedIngredient替换destination.ingredientItem = recipeItem.ingredients[0].ingredient，则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部分（或第0部分？）并将{{1}}调用移至if语句以使其更安全。

Answer 2

修正：

{{1}}

Answer 3

您的代码容易出错，因为无论如何都可以执行segue 部分
获取所选项目的更好方法是在代理内部调用indexPathForSelectedRow()方法

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    if indexPath.section == 1 {
         performSegueWithIdentifier("showIngredientInRecipe", sender: self)
    }
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "showIngredientInRecipe" {
        //get selected item
        let indexPath = self.tableView.indexPathForSelectedRow() {
            let selectedIngredient = recipeItem.ingredients[indexPath.row]
            print("selectedIngredient \n \(selectedIngredient)")
            //segue
            let svc = segue.destinationViewController as! UINavigationController
            let destination = svc.topViewController as! IngredientDetailViewController
            destination.ingredientItem = selectedIngredient
        }
    }
}

prepareForSegue首先返回nil

3 个答案: