遇到老生常谈的问题了，不知道错到哪里了。

[有图有派]

各位大佬，我在写数据库基础类，在调试的时候出现了如截图的错误，不知道该怎么处理，请大佬们指点迷津下，谢谢！


程序如下：

Option Explicit Off
Imports System.Data.SqlClient
#Region "数据库基本操作类库"
Public Class PublicClass
#Region "数据库连接类"
    Public sqlconn As New SqlClient.SqlConnection
    Public Sub open_conn()
        'Dim sqlconnstr As String
        Try
            sqlconn.ConnectionString = ("server=127.0.0.1;integrated security=False;Initial Catalog=YNCSys;User ID=sa;Pwd=adminsa226200")
        Catch ex As Exception
            Throw ex
        End Try
    End Sub
#End Region
#Region "select 语句,需要输入T-SQL语句"
    Public Function dataSelect(ByVal strsql As String, ByVal strTableName As String) As DataSet
        Dim mydataset As New DataSet
        Dim mySqlAdapter As SqlClient.SqlDataAdapter
        Try
            sqlconn.Open()
            mySqlAdapter = New SqlClient.SqlDataAdapter(strsql, sqlconn)
            mySqlAdapter.Fill(mydataset, strTableName)
            sqlconn.Close()
            mySqlAdapter = Nothing
        Catch ex As Exception
            If sqlconn.State = ConnectionState.Open Then
                sqlconn.Close()
            End If
            Throw ex
        End Try
        Return mydataset
    End Function
#End Region
#Region "数据插入操作，参数为insert语句和表名"
    Public Sub dataInsert(ByVal strSql As String, ByVal strTableName As String)
        Dim mysqlcomm As SqlClient.SqlCommand
        Try
            sqlconn.Open()
            mysqlcomm = New SqlClient.SqlCommand(strSql, sqlconn)
            mysqlcomm.ExecuteNonQuery()
            sqlconn.Close()
            mysqlcomm = Nothing
        Catch ex As Exception
            If sqlconn.State = ConnectionState.Open Then
                sqlconn.Close()
            End If
            Throw ex
        End Try
    End Sub
#End Region
#Region "修改数据模块，参数为updata和表名"
    Public Sub dataUpdate(ByVal strSql As String, ByVal strTableName As String)
        Dim mysqlcomm As New SqlClient.SqlCommand
        Try
            sqlconn.Open()
            mysqlcomm = New SqlClient.SqlCommand(strSql, sqlconn)
            mysqlcomm.ExecuteNonQuery()
            sqlconn.Close()
            mysqlcomm = Nothing
        Catch ex As Exception
            If sqlconn.State = ConnectionState.Open Then
                sqlconn.Close()
            End If
            Throw ex
        End Try
    End Sub
#End Region
#Region "删除数据操作,参数为delete和要删除的表名"
    Public Sub dataDelete(ByVal strSql As String, ByVal strTableName As String)
        Dim mysqlcomm As New SqlClient.SqlCommand
        Try
            sqlconn.Open()
            mysqlcomm = New SqlClient.SqlCommand(strSql, sqlconn)
            mysqlcomm.ExecuteNonQuery()
            sqlconn.Close()
            mysqlcomm = Nothing
        Catch ex As Exception
            If sqlconn.State = ConnectionState.Open Then
                sqlconn.Close()
            End If
            Throw ex
        End Try
    End Sub
#End Region
#Region "控件绑定方法,参数为SQL存储过程和DataGridView控件"
    Public Sub BDDataToDataGridView(ByVal PRO As String, ByVal DGV As DataGridView)
        sqlconn.Open()
        Dim sqlcmd As New System.Data.SqlClient.SqlCommand
        sqlcmd.Connection = sqlconn
        Dim da As New System.Data.SqlClient.SqlDataAdapter()
        da.SelectCommand = sqlcmd
        da.SelectCommand.CommandType = CommandType.StoredProcedure
        da.SelectCommand.CommandText = "select * from '" + PRO.ToString().Trim() + "'" '通过SQL的存储过程绑定数据
        Dim ds As New DataSet()
        da.SelectCommand.Connection = sqlconn
        da.Fill(ds)
        DGV.DataSource = ds.Tables(0)
        DGV.Refresh()
    End Sub
#Region "控件绑定方法,参数为SQL存储过程和ComboBox控件"
    Public Sub BDToComboBox(ByVal PRO As String, ByVal ComboBox As ComboBox)
        sqlconn.Open()
        Dim sqlcmd As New System.Data.SqlClient.SqlCommand
        sqlcmd.Connection = sqlconn
        Dim da As New System.Data.SqlClient.SqlDataAdapter()
        da.SelectCommand = sqlcmd
        da.SelectCommand.CommandText = "select * from '" + ComboBox.SelectedText.Trim + "'" '通过SQL的存储过程绑定数据
        Dim ds As New DataSet()
        da.SelectCommand.Connection = sqlconn
        da.Fill(ds)
        ComboBox.DataSource = ds.Tables(0)
        ComboBox.Refresh()
    End Sub
#End Region
#End Region
End Class
#End Region

[脆皮大雪糕]

错误提示那么清晰明了：connectionstring没有设置嘛 然后看你的代码，在open_conn方法里面进行了设置。那么接下来的问题就是这个方法被调用了吗？最简单的办法，在这一行加个断点，看在报错前会不会跑到这个断点就明白了。