连接已打开？？

[cat54]

在button1的点击事件里执行如下操作，con是sqlconnection是绝对没问题的
try
con.Open()
Catch exp As Exception
If exp.Message <> "" Then
Panel1.Visible = True
Exit Sub
End If
End Try
Dim a As New formmain()
Dim com As New SqlClient.SqlCommand()
com.CommandText = "select lastname from employees where lastname='" & TextBox1.Text & "'"
com.Connection = con
dap.SelectCommand = com
dap = New SqlClient.SqlDataAdapter(com)
dap.SelectCommand.ExecuteNonQuery()
ds.Clear()
dap.Fill(ds)
If ds.Tables(0).Rows.Count < 1 Then
'MsgBox(ds.Tables(0).Rows.Count)
MsgBox("非法用户")
TextBox1.Text = ""
TextBox2.Text = ""
TextBox1.Focus()
Else

loginid = TextBox1.Text
a.Show()
Me.Hide()
dap.Dispose()
ds.Clear()
com.Dispose()
End If
con.Close()

点击第一次没有关系，但连续点击就会出错说连接已经打开。

怎样解决呢

[LongBow007]

把 con.open写在try外面试试

[36B]

同意楼上的！

[icanfly_jlh]

应该把con.close()放在finally块中,这样能确保不论有异常抛出都会关闭连接
试着这样写:
==================================================

Dim a As New formmain()
Dim com As New SqlClient.SqlCommand()
com.CommandText = "select lastname from employees where lastname='" & TextBox1.Text & "'"
com.Connection = con
dap.SelectCommand = com

try
con.Open()
dap = New SqlClient.SqlDataAdapter(com)
dap.SelectCommand.ExecuteNonQuery()
ds.Clear()
dap.Fill(ds)
If ds.Tables(0).Rows.Count < 1 Then
'MsgBox(ds.Tables(0).Rows.Count)
MsgBox("非法用户")
TextBox1.Text = ""
TextBox2.Text = ""
TextBox1.Focus()
Else

loginid = TextBox1.Text
a.Show()
Me.Hide()
dap.Dispose()
ds.Clear()
com.Dispose()
End If
Catch exp As Exception
'你的处理
'Exit Sub 不需要
finally
con.Close()
End Try

[cnhgj]

if con.state.tostring = "closed" then
con.open()
end if
先判断连接是否关闭，如果关闭再open

[CMIC]

try
If Not cn.State = ConnectionState.Open Then
con.Open()
End If
.......

[cat54]

感谢！