未将对象引用设置到对象的实例。急
未将对象引用设置到对象的实例。
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。
异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。
源错误:
行 35： sqlconn = New SqlConnection(constr)
行 36：
行 37： sqlconn.Open()
行 38： Dim daohang As SqlCommand
行 39： Dim daohangreader As SqlDataReader
--------------
行 37： sqlconn.Open()报错
源码如下:
Imports System.Data.SqlClient
Imports System.Data
Public Class top
Inherits System.Web.UI.UserControl
#Region " Web 窗体设计器生成的代码 "
'该调用是 Web 窗体设计器所必需的。
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
End Sub
Protected WithEvents ImageButton1 As System.Web.UI.WebControls.ImageButton
Protected WithEvents Label1 As System.Web.UI.WebControls.Label
'注意: 以下占位符声明是 Web 窗体设计器所必需的。
'不要删除或移动它。
Private designerPlaceholderDeclaration As System.Object
Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
'CODEGEN: 此方法调用是 Web 窗体设计器所必需的
'不要使用代码编辑器修改它。
InitializeComponent()
End Sub
#End Region
'Protected root As String = ConfigurationSettings.AppSettings( "webroot ")
Protected webtitle As String = ConfigurationSettings.AppSettings( "webtitle ")
Private constr As String = ConfigurationSettings.AppSettings( "app_connstr ")
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'在此处放置初始化页的用户代码
If Not Page.IsPostBack Then
Dim sqlconn As SqlConnection
sqlconn = New SqlConnection(constr)
sqlconn.Open()
Dim daohang As SqlCommand
Dim daohangreader As SqlDataReader
daohang = New SqlCommand( "select Video_TypeName,Video_TypeID from tb_VideoType ", sqlconn)
daohangreader = daohang.ExecuteReader()
While daohangreader.Read
Label1.Text += "| <A href= 'list.aspx?type_id= " + daohangreader.Item( "Video_TypeID ").ToString + " '> " + daohangreader.Item( "Video_TypeName ").ToString + " </a> "
End While
daohangreader.Close()
sqlconn.Close()
End If
End Sub
End Class
--------------
Web.config
<configuration>
<appSettings>
<add key= "app_connstr " value= "Data Source=.;uid=sa;pwd=;database=eMedia "/>
-------------
Web.config在根目录下,报错文件在次目录下
--------
断点调试.报这个错误
ServerVersion <error: an exception of type: {System.InvalidOperationException} occurred> String
[解决办法]
<add key= "app_connstr " value= "Data Source=.;uid=sa;pwd=;database=eMedia "/>
你的數據庫鏈接字符串有問題。
"Data Source=Aron1;Initial Catalog=pubs;User Id=myUsername;Password=myPassword; "
具體的 鏈接方法看這個網站
http://www.connectionstrings.com/index.asp
[解决办法]
<add key= "app_connstr " value= "Data Source=.;Initial Catalog=eMedia;persist security info=True;User Id=sa;Password=; "/>
同时检查下Sql的Sa用户密码是否为空
[解决办法]
数据库连接字符串问题,其实不用自己写,有个方法取到:
从工具箱--数据选项卡--拖也个sqldataAdapter组件,它会自动生成这个连接字符串的(配制下就行了).
LZ可以试下
[解决办法]
发个我平常用的一个Sql操作类，用此类试试
'****************************************************************************************************
'类名：clsSqlDb
'说明：SQLServer数据库相关处理类
'引用：System.Data.SqlClient
'编辑：雅博
'****************************************************************************************************
Imports System.Data
Imports System.Data.SqlClient
Public Class clsSqlDb
'1.定义接口
'1-1.数据库连接字符串接口
Private vConnStr As String = " "
Public Property ConnStr() As String
Get
Return vConnStr
End Get
Set(ByVal value As String)
vConnStr = value
End Set
End Property
'1-2.定义传递的信息字符
Private vMessageInfo As String = " "
Public Property MessageInfo() As String
Get
Return vMessageInfo
End Get
Set(ByVal value As String)
vMessageInfo = value
End Set
End Property
'重写New
Public Sub New(Optional ByVal vConnString As String = " ")
If vConnString.Trim <> " " Then ConnStr = vConnString
End Sub
'2.操作的过程函数
'2-1.定义检查数据记录是否存在
Public Function IsRecordExists(ByVal sqlString As String) As Boolean
MessageInfo = " "
Dim myCn As New SqlConnection(ConnStr)
Try
myCn.Open()
Dim myCmd As New SqlCommand(sqlString, myCn)
Dim dr As SqlDataReader = myCmd.ExecuteReader
Dim i As Integer = 0
While dr.Read
i += 1
Exit While
End While
dr.Close()
If i > 0 Then
MessageInfo = "数据记录存在。 "
Return True
Else
MessageInfo = "数据记录不存在。 "
Return False
End If
Catch ex As Exception
MessageInfo = ex.ToString.Trim + "。 "
Return False
Finally
If myCn.State = ConnectionState.Open Then myCn.Close()
myCn = Nothing
End Try
End Function
'2-2.定义执行SQL语句
Public Function ExecuteSqlString(ByVal sqlString As String) As Boolean
Dim myCn As New SqlConnection(ConnStr)
Try
myCn.Open()
Dim myCmd As New SqlCommand(sqlString, myCn)
Dim dr As SqlDataReader = myCmd.ExecuteReader()
MessageInfo = "执行SQL语句完成。 "
Return True
Catch ex As Exception
MessageInfo = ex.ToString.Trim + "。 "
Return False
Finally
If myCn.State = ConnectionState.Open Then myCn.Close()
myCn = Nothing
End Try
End Function
'2-3.定义取得表单中某一个特定条件下的具体字段的值
Public Function GetFieldValueFromTableBySqlString(ByVal sqlStr As String) As String
Dim fieldValueString As String = " "
Dim myCn As New SqlConnection(ConnStr)
Try
myCn.Open()
Dim myCmd As New SqlCommand(sqlStr, myCn)
Dim Dr As SqlDataReader = myCmd.ExecuteReader
While Dr.Read
fieldValueString = Dr(0).ToString.Trim
Exit While
End While
Dr.Close()
Catch ex As Exception
Finally
If myCn.State = ConnectionState.Open Then myCn.Close()
myCn = Nothing
End Try
Return fieldValueString
End Function
'2-4.定义取得表单中某一个特定条件下的具体字段的值
Public Function GetFieldValueFromTableByOtherFieldLimit(ByVal conditionFieldName As String, ByVal conditionFieldValue As String, ByVal GetValueFieldName As String, ByVal tableName As String) As String
Dim sqlStr As String = "select " & GetValueFieldName & " from " & tableName & " where " & conditionFieldName & "= ' " & conditionFieldValue & " ' "
Return GetFieldValueFromTableBySqlString(sqlStr)
End Function
'2-5.获得DataSet
Public Function GetDataSetBySql(ByVal sqlString As String) As DataSet
Try
Dim adapter As SqlDataAdapter = New SqlDataAdapter(sqlString, ConnStr)
Dim ds As New DataSet
adapter.Fill(ds)
Return ds
Catch ex As Exception
Return Nothing
End Try
End Function
'2-6.定义获得DataTable
Public Function GetDataTableBySql(ByVal sqlstring As String) As DataTable
Try
Dim adapter As SqlDataAdapter = New SqlDataAdapter(sqlstring, ConnStr)
Dim tbl As New DataTable
adapter.Fill(tbl)
Return tbl
Catch ex As Exception
Return Nothing
End Try
End Function
'2-7.获得数据项目
Public Function GetDataToStrBySql(ByVal sqlstring As String, ByVal ColSplit As String, ByVal RowSplit As String) As String
If ColSplit = " " Then ColSplit = "| "
If RowSplit = " " Then RowSplit = "√ "
Dim ds As DataSet = GetDataSetBySql(sqlstring)
Dim str As String = " "
If Not ds Is Nothing Then
If ds.Tables.Count > 0 Then
Dim tbl As DataTable = ds.Tables(0)
Dim i As Integer = 0, j As Integer = 0, k As Integer = tbl.Rows.Count
Dim strR(k) As String
Dim row As DataRow
For Each row In tbl.Rows
strR(i) = row(0).ToString.Trim
For j = 1 To tbl.Columns.Count - 1
strR(i) += ColSplit + row(j).ToString.Trim
Next
i += 1
Next
str = strR(0)
For j = 1 To i - 1
str += RowSplit + strR(j)
Next
End If
End If
Return str
End Function
'2-8.定义获取数据库连接字符串
Public Function GetConnectionString(ByVal Param_DataSource As String, ByVal Param_DbName As String, ByVal Param_SSPI As String, ByVal Param_UID As String, ByVal Param_Psw As String) As String
Dim myConnStr As String = "Data Source= " + Param_DataSource + ";Initial Catalog= " + Param_DbName
If LCase(Param_SSPI) = "sspi " Then
myConnStr += ";integrated security=SSPI;persist security info=False; "
Else
myConnStr += ";persist security info=True;user id= " + Param_UID & ";password= " + Param_Psw
End If
Return myConnStr
End Function
'2-9.定义检查数据库服务器连接是否正常
Public Function IsSqlConnectionSucceed(ByVal cnSrv As String, ByVal cnSSPI As String, ByVal cnUid As String, ByVal cnPsw As String) As Boolean
Dim myCn As SqlConnection = Nothing
Dim Param_ConnStr As String = Me.GetConnectionString(cnSrv, "master ", cnSSPI, cnUid, cnPsw)
MessageInfo = " "
Try
myCn = New SqlConnection(Param_ConnStr)
myCn.Open()
If myCn.State = ConnectionState.Open Then
MessageInfo = "数据库连接成功。 "
Return True
Else
MessageInfo = "数据库连接不成功。 "
Return False
End If
Catch ex As Exception
MessageInfo = ex.Message.Trim
Return False
Finally
If myCn.State = ConnectionState.Open Then myCn.Close()
If Not myCn Is Nothing Then myCn = Nothing
End Try
End Function
End Class
[解决办法]
daohang = New SqlCommand( "select Video_TypeName,Video_TypeID from tb_VideoType ", sqlconn)
字段和数据库里字段是否有出入
[解决办法]
你没连上数据库..连接字符串没写错.是你登录错误.
给你一个验证sa密码的方法:
sql-> 查询分析器-> File-> 连接-> sqlserver身份验证...试试你能不能用sa+空密码登录.如果不能就去sql的安全里重设密码.OK.
