从字符串“”到类型 'Integer' 的转换在 for each 语句上无效

Question

正如标题所说，我从下面的代码中得到一个错误，它基本上选择 ListView 上的多个输入，并将其放入数据库中。这是代码：

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        For Each item As ListViewItem In ListView1.SelectedItems
        Dim StudentID = Integer.Parse(item.SubItems(0).Text)
        Dim FirstName = item.SubItems(1).Text
        Dim LastName = item.SubItems(2).Text
            DBConn()
            SQLSTR = "INSERT INTO '" & TextBox4.Text & "' (StudentID, FirstName, LastName) VALUES ('" & StudentID & "', '" & FirstName & "', '" & LastName & "') "
            alterDB()
            MsgBox("Students succesfully added", msgboxtitle)
        Next
    MsgBox("Students added!", , msgboxtitle)
End Sub

准确的错误是：

An unhandled exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll

Additional information: Conversion from string "" to type 'Integer' is not valid.

Answer 1

您可以使用CInt() 转换为整数。 MSDN Reference

我建议在定义变量之前 Dim variable As Type。

    Dim item As ListViewItem        
    Dim StudentID as Integer
    Dim FirstName as String
    Dim LastName as String

    For Each item In ListView1.SelectedItems
        StudentID = CInt(item.SubItems(0).Text)
        FirstName = item.SubItems(1).Text
        LastName = item.SubItems(2).Text

从字符串“”到类型 'Integer' 的转换在 for each 语句上无效

Conversion from string "" to type 'Integer' is not valid on a for each statement

sql

vb.net

string

integer

type-conversion