未设置对象实例的对象变量

Question

仅仅因为（在我的代码中）有些时候看起来sqlDataReader被打开并告诉我“已经有一个打开的数据读取器”
我决定放这一行： If Not SqlReader.IsClosed Then SqlReader.Close()

Select Case PreviousRecord 
    Case True 
     SqlComm = New SqlCommand("Select * from " & tmpName & " where FuelOrderValid = '" & True & "' Order by FuelLoadDate", ReportsSQLConn) 
    Case False 
     SqlComm = New SqlCommand("Select * from " & tmpName & " where FuelOrderValid = '" & True & "' And FuelOrderID = '" & ordNum & "' Order by FuelLoadDate", ReportsSQLConn) 
End Select  

If Not SqlReader.IsClosed Then SqlReader.Close() 

If SqlComm.Connection.State = Data.ConnectionState.Open Then 
    SqlReader = SqlComm.ExecuteReader(CommandBehavior.KeyInfo) 
Else 
    SqlComm.Connection.Open() 
    SqlReader = SqlComm.ExecuteReader(CommandBehavior.KeyInfo) 
End If 

但是现在，当它涉及到执行
If Not SqlReader.IsClosed Then SqlReader.Close()
它给出了错误的指令：
Object Variable Not Set To An Instance Of An Object
我实在无法理解WH y正在这样做。
请问有人帮我吗？

Answer 1

在致电SqlReader.IsClosed和SqlReader.Close之前SqlReader尚未初始化。你可以检查它的nothing是否这样：

If SqlReader IsNot Nothing Then 
    ' Do something with the SqlReader' 
Else 
    ' Create a new SqlReader' 
End If