Asp.net 在数据库表中填写登录页信息时发生以下错误

对象引用未设置为对象的实例

Source Error: 


Line 17:     {
Line 18:         SqlConnection cnn = new SqlConnection(@"Data Source=.\SQLEXPRESS;Initial Catalog=class;Integrated Security=True");
Line 19:         cnn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["sqlconnection "].ConnectionString;
Line 20:         cnn.Open();
Line 21:         SqlCommand cmd = new SqlCommand();

Source File: c:\Users\VIJU\Documents\Visual Studio 2010\WebSites\Class\Default2.aspx.cs    Line: 19 

描述：执行当前web请求期间发生未处理的异常。请查看堆栈跟踪以了解有关错误的更多信息以及错误在代码中的起源

异常详细信息：

System.NullReferenceException

：对象引用未设置为对象的实例

Source Error: 


Line 17:     {
Line 18:         SqlConnection cnn = new SqlConnection(@"Data Source=.\SQLEXPRESS;Initial Catalog=class;Integrated Security=True");
Line 19:         cnn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["sqlconnection "].ConnectionString;
Line 20:         cnn.Open();
Line 21:         SqlCommand cmd = new SqlCommand();

Source File: c:\Users\VIJU\Documents\Visual Studio 2010\WebSites\Class\Default2.aspx.cs    Line: 19 

堆栈跟踪：

[NullReferenceException: Object reference not set to an instance of an object.]
   Default2.Button1_Click(Object sender, EventArgs e) in c:\Users\VIJU\Documents\Visual Studio 2010\WebSites\Class\Default2.aspx.cs:19
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +118
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +112
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563

我猜是这样的：

cnn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["sqlconnection "].ConnectionString

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我打赌sqlconnection不存在，或者在您的web.config中拼写错误。

我认为您的连接字符串键名有问题。 更正如下：

cnn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["sqlconnection"].ConnectionString;

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请添加aspx文件的代码和您的代码隐藏文件。