如果代码在通过 try 语句之前，如何运行编码

Question

我知道我的标题信息量不大，而且在我看来很难表达。在 visual basic 中，我的目标是运行一段代码，如果它之前的代码通过了 try 语句，而不是运行如果它没有通过 try 语句。

我的代码如下：

Public Class Form2
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim newCustomersRow As DataRow = Form1.Book_StoreDataSet.Customer.NewRow()
        newCustomersRow("Title") = TextBox1.Text()
        newCustomersRow("First Name") = TextBox2.Text()
        newCustomersRow("Last Name") = TextBox3.Text()
        newCustomersRow("Address Line 1") = TextBox4.Text()
        newCustomersRow("Town") = TextBox5.Text()
        newCustomersRow("County") = TextBox6.Text()
        newCustomersRow("Post Code") = TextBox7.Text()
        newCustomersRow("Card Type") = TextBox8.Text()
        newCustomersRow("Card Number") = TextBox9.Text()
        Try
            newCustomersRow("Expiry Date") = TextBox10.Text()
        Catch ex As ArgumentException
            MsgBox("Please enter date like this: DD/MM/YY.")
            TextBox1.Text = ""
            TextBox2.Text = ""
            TextBox3.Text = ""
            TextBox4.Text = ""
            TextBox5.Text = ""
            TextBox6.Text = ""
            TextBox7.Text = ""
            TextBox8.Text = ""
            TextBox9.Text = ""
            TextBox10.Text = ""
        End Try
        Try
            Form1.Book_StoreDataSet.Customer.Rows.Add(newCustomersRow)
            MsgBox("Data added successfully")
            TextBox1.Text = ""
            TextBox2.Text = ""
            TextBox3.Text = ""
            TextBox4.Text = ""
            TextBox5.Text = ""
            TextBox6.Text = ""
            TextBox7.Text = ""
            TextBox8.Text = ""
            TextBox9.Text = ""
            TextBox10.Text = ""
        Catch a As ConstraintException
            MsgBox("That Card Number already exists.")
        End Try
    End Sub
End Class

每次它运行都会显示 "Data added successfully"，即使出现错误也是如此。

Answer 1

所以，简而言之，您遇到了以下问题：

Try
   A
Catch SomeExceptionThrownByA
   B
End Try

C?  ' only run this if there was no exception before

对吗？

解决这个问题的方法很少。因为，在你的情况下，你想跳过 all 以下代码，最简单的代码是：

选项 1

Try
   A
Catch SomeExceptionThrownByA
   B
   Return
End Try

C

备选方案是：

选项 2

Try
   A
   C
Catch SomeExceptionThrownByA
   B
End Try

或

选项 3

Dim success = False
Try
   A
   success = True
Catch SomeExceptionThrownByA
   B
End Try

If success Then
   C
End If

就个人而言，如果可能的话，我更喜欢选项 1，否则我更喜欢选项 3，因为它使 Try-Catch 块变短。我不太喜欢选项 2，因为它

使 Catch 块应该捕获块 A（而不是块 C）和
如果 C 也可以抛出 SomeExceptionThrownByA，事情就变得复杂了。

Answer 2

您可以嵌套 Try/Catch 得到您想要的结果。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim newCustomersRow As DataRow =    Form1.Book_StoreDataSet.Customer.NewRow()
    newCustomersRow("Title") = TextBox1.Text()
    newCustomersRow("First Name") = TextBox2.Text()
    newCustomersRow("Last Name") = TextBox3.Text()
    newCustomersRow("Address Line 1") = TextBox4.Text()
    newCustomersRow("Town") = TextBox5.Text()
    newCustomersRow("County") = TextBox6.Text()
    newCustomersRow("Post Code") = TextBox7.Text()
    newCustomersRow("Card Type") = TextBox8.Text()
    newCustomersRow("Card Number") = TextBox9.Text()
    Try
        newCustomersRow("Expiry Date") = TextBox10.Text()
         Try
             Form1.Book_StoreDataSet.Customer.Rows.Add(newCustomersRow)
             MsgBox("Data added successfully")
             TextBox1.Text = ""
             TextBox2.Text = ""
             TextBox3.Text = ""
             TextBox4.Text = ""
             TextBox5.Text = ""
             TextBox6.Text = ""
             TextBox7.Text = ""
             TextBox8.Text = ""
             TextBox9.Text = ""
             TextBox10.Text = ""
         Catch a As ConstraintException
             MsgBox("That Card Number already exists.")
         End Try

    Catch ex As ArgumentException
        MsgBox("Please enter date like this: DD/MM/YY.")
        TextBox1.Text = ""
        TextBox2.Text = ""
        TextBox3.Text = ""
        TextBox4.Text = ""
        TextBox5.Text = ""
        TextBox6.Text = ""
        TextBox7.Text = ""
        TextBox8.Text = ""
        TextBox9.Text = ""
        TextBox10.Text = ""
    End Try

End Sub
 End Class

Answer 3

在我看来，将验证提取到不同的方法中会更好。

所以（原谅语法，我的 VB 已经有一段时间了）：

Private Sub Button1_Click(sender As Object, e As EventArgs)     
     var isValid = ValidateData()
     if (!isValid) then 
        MessageBox....
        return
     end if
     try 
        Form1.Book_StoreDataSet.Customer.Rows.Add(newCustomersRow)
        ....
     catch
     ...

我之所以这么说，是因为当您想要或需要验证其他数据时会发生什么？通过分离验证，您可以更加灵活并保持代码更简洁。

Answer 4

在我看来，使用 Try..Catch..End Try 进行数据验证并不理想。当然，最好使用 Date.TryParse 而不是像下面的代码，并使用 If .. End If 检查对象是否已存在于数据集中？

老实说，使用这种方法来捕获输入不正确的日期是有缺陷的。如果有人试图将 2016 年 6 月 8 日输入为 08/06/2016，它不会被您的有效性测试捕获。最好改用 DateTimePicker。

    If Not Date.TryParse(TextBox10.Text, newCustomersRow("Expiry Date")) Then
        MsgBox("Please enter date like this: DD/MM/YY.")
        TextBox1.Text = ""
        TextBox2.Text = ""
        TextBox3.Text = ""
        TextBox4.Text = ""
        TextBox5.Text = ""
        TextBox6.Text = ""
        TextBox7.Text = ""
        TextBox8.Text = ""
        TextBox9.Text = ""
        TextBox10.Text = ""
    Else
        Try
            Form1.Book_StoreDataSet.Customer.Rows.Add(newCustomersRow)
            MsgBox("Data added successfully")
            TextBox1.Text = ""
            TextBox2.Text = ""
            TextBox3.Text = ""
            TextBox4.Text = ""
            TextBox5.Text = ""
            TextBox6.Text = ""
            TextBox7.Text = ""
            TextBox8.Text = ""
            TextBox9.Text = ""
            TextBox10.Text = ""
        Catch a As ConstraintException
            MsgBox("That Card Number already exists.")
        End Try
    End If

如果代码在通过 try 语句之前，如何运行编码

How to run code if the code before it passes a try statement

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如果代码在通过 try 语句之前，如何 运行 编码

How to run code if the code before it passes a try statement

vb.net

visual-studio-2010

如果代码在通过 try 语句之前，如何运行编码