Question

您好，我正在开发一个非常小的Windows应用程序，试图再次进入事物的摇摆。我遇到的问题是，当没有检查单选按钮时，我试图抛出异常，以便出现一个消息框告诉用户选择一个单选按钮。但是，我无法记住抛出什么异常或如何实现它。我已经提供了一个小代码片段供您查看我是如何做到这一点的。我打算在if语句之后添加一个else语句，但是不记得要抛出什么。该应用程序是一个非常基本的小型计算器。

 if ((bool)Addition.IsChecked.HasValue && Addition.IsChecked.Value)
            {
                calcualteAdditionSum(val1, val2);
            }

            if ((bool)Subtract.IsChecked.HasValue && Subtract.IsChecked.Value)
            {
                calculateSubtractSun(val1, val2);
            }

            if ((bool)Remainder.IsChecked.HasValue && Remainder.IsChecked.Value)
            {
                calculateRemainderSun(val1, val2);
            }

            if ((bool)Multiply.IsChecked.HasValue && Multiply.IsChecked.Value)
            {
                calculateMultiplySum(val1, val2);
            }

            if ((bool)Division.IsChecked.HasValue && Division.IsChecked.Value)
            {
                calculateDivisionSum(val1, val2);
            }


        }

        catch
        {
            MessageBox.Show("Please ensure you have selected a checkBox\nand provided a number in the textboxes");
        }

Answer 1

你不必抛出异常或抓住任何东西。只需创建一个bool变量，并在过程开始时将其初始化为false。如果选择了任何按钮，此变量将存储信息。在每个true块内将其值更改为if，并在结尾处检查其状态。如果它仍然是false，请显示一条消息。

修改

基本上，当发生不好的事情时，你应该抛出异常。我不会将选择任何单选按钮归类为坏事。

Answer 2

我会将第2，第3，第4和第5个{-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE ConstraintKinds #-} import GHC.TypeLits newtype Field (n :: Symbol) v = Field { unField :: v } deriving Show data Person1 = Person1 { _age :: Field "age" Int , _name :: Field "name" String } data Person2 = Person2 { _age' :: Field "age" Int , _name' :: Field "name" String , _lib' :: Field "lib" String } deriving instance Show Person1 deriving instance Show Person2 data Label (l :: Symbol) = Get class Has a l b | a l -> b where from :: a -> Label l -> b instance Has Person1 "age" Int where from (Person1 a _) _ = unField a instance Has Person1 "name" String where from (Person1 _ a) _ = unField a instance Has Person2 "age" Int where from (Person2 a _ _) _ = unField a instance Has Person2 "name" String where from (Person2 _ a _) _ = unField a age :: Has a "age" b => a -> b age pnt = from pnt (Get :: Label "age") name :: Has a "name" b => a -> b name pnt = from pnt (Get :: Label "name") -- Parameterized constraint kind for "Simon-ness" of a record. type Simon a = (Has a "name" String, Has a "age" Int) spj :: Person1 spj = Person1 (Field 56) (Field "Simon Peyton Jones") smarlow :: Person2 smarlow = Person2 (Field 38) (Field "Simon Marlow") (Field "rts") catNames :: (Simon a, Simon b) => a -> b -> String catNames a b = name a ++ name b addAges :: (Simon a, Simon b) => a -> b -> Int addAges a b = age a + age b names :: String names = name smarlow ++ "," ++ name spj -- "Simon Marlow,Simon Peyton Jones" ages :: Int ages = age spj + age smarlow -- 94语句更改为if语句（除非我错过了某些内容 - 如果他们是单选按钮，那么它似乎不可能一次有多个条件）然后我会在结尾添加一个else if语句，显示一个消息框，向用户解释选择单选按钮之一。不需要例外。

在没有选择单选按钮时尝试抛出异常

2 个答案: