Question

这是我的代码。我一直有错误“类型字符串的值无法转换为system.data.datatable”

Function GetTable() As DataTable
        Dim SQLConnection As New SqlConnection(ConfigurationManager.ConnectionStrings("Zeinchatconnection").ToString())
        Dim CommSQL As New SqlClient.SqlCommand
        Dim ChatDataAdapter As SqlDataAdapter
        Dim paramSQL As SqlClient.SqlParameter
        Dim DStable As DataSet
        Dim table As New DataTable
        Dim szName As String = ""
        Dim szNumber As String = ""
        Try
            If SQLConnection.State = ConnectionState.Closed Then
                SQLConnection.Open()
            End If
            CommSQL.Connection = SQLConnection
            CommSQL.CommandType = CommandType.StoredProcedure
            CommSQL.CommandText = "spc_newselect"



        CommSQL.ExecuteNonQuery()

        ChatDataAdapter = New SqlDataAdapter(CommSQL)
        ChatDataAdapter.Fill(DSTable)

        table.Rows.Clear()
        table.Clear()
        table = DStable.Tables(0)

        Dim i As Integer = 0

        For i = 0 To table.Rows.Count - 1
            szName = szName & "  " & table.Rows(i).Item(0) & table.Rows(i).Item(1)
            szNumber = szNumber & "  " & table.Rows(i).Item(0) & table.Rows(i).Item(1)
        Next

        GetTable = "1"
    Catch ex As System.Data.SqlClient.SqlException
        GetTable = "0"
    Catch ex As Exception
        GetTable = "0"

        If (IsNothing(ChatDataAdapter) = False) Then ChatDataAdapter.Dispose()
        If (IsNothing(CommSQL) = False) Then CommSQL.Dispose()
        SQLConnection.Close()
    End Try
    Return table


End Function

错误所在的部分是gettable =“1”及以下。

Answer 1

您的函数GetTable会返回DataTable

您无法将"1"转换为DataTable，因为消息显示行GetTable = "1"

上发生了什么

如果您想返回DataTable并设置标志以查看状态;改变你的函数定义：

Function GetTable(byref result as Integer) As DataTable

然后代替GetTable = "1"将其更改为result = 1。这样，您可以检查结果值并返回DataTable：

Dim res as Integer
Dim dt as DataTable = GetTable(res)
If res = 1 then
    'It worked!
End If

旁注：启用选项严格

Answer 2

GetTable = "1"表示您要设置函数的returnValue。由于您的函数定义为Function GetTable() As DataTable，因此编译器会显示错误！

下面几行有一个正确的返回标准（Return table）所以我不确定你的目标是GetTable = "1"？

我认为您希望有一个额外的returnValue来指示您的函数调用是否成功。但事实上，函数可能只有一个returnValue。

您可以选择将表格var设置为空，或使用参数参数...

' possible solution 1 - using nothing value
Function GetTable() As DataTable
    Try
        ' your code goes here
        ' remove GetTable = "1" 
    Catch ex as Exception
        ' change GetTable = "0" to 
        table = nothing
    End Try
    ' other code ...
End Function

' possible solution 2 - ref param
Function GetTable(ByRef status as integer) as DataTable
   Try
        ' your code goes here
        ' remove GetTable = "1" 
        status = 1
    Catch ex as Exception
        ' change GetTable = "0" to 
        status = 0
    End Try
    ' other code ...
End Function

在解决方案2中，您还可以选择布尔参数，表示您的通话成功与否。

'vb.net中的类型字符串的值无法转换为system.data.datatable'

2 个答案: