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，出现未经处理的异常。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 10: class CommonDB行 11: {行 12: static string strConn = System.Configuration.ConfigurationSettings.AppSettings["strConn"].ToString();行 13: public static DataSet getDataSet(string sql)行 14: {
源文件: F:\Users\Visual Studio\Enterprise\DAL\CommonDB.cs 行: 12
堆栈跟踪:
[NullReferenceException: 未将对象引用设置到对象的实例。] DAL.CommonDB..cctor() in F:\Users\Visual Studio\Enterprise\DAL\CommonDB.cs:12[TypeInitializationException: “DAL.CommonDB”的类型初始值设定项引发异常。] DAL.CommonDB.getDataSet(String sql) in F:\Users\Visual Studio\Enterprise\DAL\CommonDB.cs:21 DAL.UserDB.isUserExist(String username, String userpwd) in F:\Users\Visual Studio\Enterprise\DAL\UserDB.cs:21 BLL.UserBLL.isUserExist(String username, String userpwd) in F:\Users\Visual Studio\Enterprise\BLL\UserBLL.cs:16 Web.Login.btnSubmit_Click(Object sender, EventArgs e) in F:\Users\Visual Studio\Enterprise\Web\Login.aspx.cs:24 System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9692746 System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +108 System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +12 System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +15 System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3562
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