使用VB连接数据库时出错 [英] Error at connection to database using VB

问题描述

我的代码和/或连接需要帮助。我收到的错误是：



系统类型的未处理异常。 System.Data.dll中发生InvalidOperationException



附加信息：ExecuteReader需要一个开放且可用的连接。连接的当前状态已关闭。



在此代码中:(第4行）

I need help on my codes and/or connection.I'm getting an error that says:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll

Additional information: ExecuteReader requires an open and available Connection. The connection's current state is closed.

In this code:(Line 4)

cmd.Connection = cn
        cmd.CommandText = "SELECT ID, LastName, FirstName FROM tblMembers WHERE ID = @ID"
        cmd.Parameters.Add(New SqlClient.SqlParameter("@ID", SqlDbType.Int)).Value = dg1.Item(0, e.RowIndex).Value
        dr = cmd.ExecuteReader
        If dr.HasRows() Then
            With dr
                .Read()
                txtLname.Text = dr("LastName")
                txtFname.Text = dr("FirstName")
            End With
        End If

但是如果我尝试打开连接。发生这种情况。



System.Data.dll中出现未处理的System.InvalidOperationException类型异常



附加信息：连接未关闭。连接的当前状态是打开的。



使用以下代码:(第1行）

But if I try to open the connection. This happens.

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll

Additional information: The connection was not closed. The connection's current state is open.

With this code:(Line 1)

cn.Open()
        cmd.Connection = cn
        cmd.CommandText = "SELECT ID, LastName, FirstName FROM tblMembers WHERE ID = @ID"
        cmd.Parameters.Add(New SqlClient.SqlParameter("@ID", SqlDbType.Int)).Value = dg1.Item(0, e.RowIndex).Value
        dr = cmd.ExecuteReader
        If dr.HasRows() Then
            With dr
                .Read()
                txtLname.Text = dr("LastName")
                txtFname.Text = dr("FirstName")
            End With
        End If

我尝试了什么：



我尝试运行调试而不用打开连接，它说我需要在第4行打开连接（Executereader），但是如果我打开连接，它说连接没有关闭。

What I have tried:

I tried to run the debug without opening the connection and it says I need to open the connection at line 4 (Executereader) but if I open the connection, it says that the connection was not closed.

推荐答案

信息不足。我猜你在其他地方有代码打开连接但从不关闭它。



所有连接对象都应该在你完成后创建和处理它。一个非常简单的方法是使用语句：

Not enough information. I'm going to guess that you have code elsewhere that opens a connection but never closes it.

All connection objects should be created and disposed when you're finished with it. A very simple way of doing that is the using statement:

using (var conn = new SqlConnection(...))
{
    ... your command and query code goes here ...
}

我怀疑这里有问题：

I suspect a problem here:

cn.Open()
cmd.Connection = cn

但是因为我们有不知道那些对象是什么，不可能给出明确的答案。

But since we have no idea of what are those objects, it impossible to give a definitive answer.

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