请帮我解决错误 [英] Please help me regarding the error

问题描述

大家好

我收到以下错误消息..请告诉我该怎么解决

Hi all

I am getting the below error..please tell me what the solution

Unable to cast object of type 'System.InvalidOperationException' to type 'System.Data.OleDb.OleDbDataReader'.

Private Sub FillList()
    With lvList .Clear() 
        .View = View.Details
        .FullRowSelect = True
        .GridLines = True
        .Columns.Add("Customer ID", 100)
        .Columns.Add("Company Name", 150)
        .Columns.Add("Contact Name", 140)
        .Columns.Add("Contact Title", 130)
        .Columns.Add("Address", 200)
        FillListView(lvList, GetData(sSql)) 'This is line that raises the error 
    End With
End Sub

Public Function GetData(ByVal sSQL As String)
    Dim cnCustomers As OleDbConnection Dim sqlCmd As OleDbCommand = New OleDbCommand(sSQL)
    Dim myData As OleDbDataReader cnCustomers = New OleDbConnection(cnString)
        Try
            cnCustomers.Open()
            sqlCmd.Connection = cnCustomers
            myData = sqlCmd.ExecuteReader
            Return myData
        Catch ex As Exception
            Return ex 
        End Try
End Function

推荐答案

如果看不到引发此异常的代码，就不可能告诉您出什么问题了.

但是，从该消息中，您正在尝试将一种异常类型强制转换为OleDbDataReader.显然这是行不通的.

Without seeing the code that''s throwing this exception it''s impossible to tell you what''s wrong.

But, from the message, you''re trying to cast one of the Exception types to an OleDbDataReader. That''s obviously not going to work.

这是实际的问题

this is actual problem

Public Function GetData(ByVal sSQL As String)
        Dim cnCustomers As OleDbConnection
        Dim sqlCmd As OleDbCommand = New OleDbCommand(sSQL)
        Dim myData As OleDbDataReader

        cnCustomers = New OleDbConnection(cnString)

        Try
            cnCustomers.Open()

            sqlCmd.Connection = cnCustomers

            myData = sqlCmd.ExecuteReader

            Return myData
        Catch ex As Exception
            Return ex 
        End Try
    End Function

查看带下划线的部分进行比较
发生异常时，它返回ex，它是 Exception class
的对象 通常情况下，它会返回 OleDbDataReader mydata

还有你的
FillListView将第二个参数用作 OleDbDataReader

因此，请更改该return语句，

see underlined portion compare them
when exception occur it return ex which is object of Exception class
and in normal case it returns OleDbDataReader mydata

and your
FillListView is taking second argument as OleDbDataReader

so change that return statement,

Catch ex As Exception
         Return Nothing  'or Return new OleDbDataReader()
     End Try

祝您编码愉快！
:)

Happy Coding!
:)

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