Question

我知道我的标题不是很有用，而且我认为这很难说。在visual basic中，我的目标是在代码传递给try语句之前运行一段代码，但如果它没有通过try语句则不运行它。

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

每次运行时都说＆＃34;数据成功添加＆＃34;即使有错误。

Answer 1

因此，简而言之，您遇到以下问题：

Try
   A
Catch SomeExceptionThrownByA
   B
End Try

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

右？

解决这个问题的方法很少。因为，在您的情况下，您想要跳过 all 以下代码，最简单的是：

选项1

Try
   A
Catch SomeExceptionThrownByA
   B
   Return
End Try

C

替代方案是：

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，否则选择选项3，因为它会使Try-Catch块保持简短。我不喜欢选项2，因为它

使得Catch块不应该在块A（而不是块C）和
如果C也可以抛出SomeExceptionThrownByA。

Answer 2

在我看来，通过将验证推广到不同的方法，您会得到更好的服务。

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
     ...

我之所以这样说是您希望或需要验证其他数据时会发生什么？通过分离验证，您可以为自己提供更大的灵活性并使代码更清晰。

Answer 3

你可以嵌套Try / Catch去获得你想要的结果。

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 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代替下面的代码并使用If .. End If来检查数据集中是否已存在该对象？

说实话，使用这种方法捕捉不正确输入的日期是有缺陷的。如果有人试图在2016年6月8日进入2016年6月8日，则不会被您的有效性测试所捕获。最好使用DateTimePicker代替。

    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

如果代码在传递try语句之前如何运行代码

4 个答案: