我使用以下代码进行登录。
public logininfo ViewLoginByUsernameAndPassword(logininfo linfo)
{
logininfo linf = null;
SqlDataReader dr = null;
try
{
con.Open();
SqlCommand com = new SqlCommand("adminlogin", con);
com.CommandType = CommandType.StoredProcedure;
SqlParameter q = new SqlParameter();
q = com.Parameters.AddWithValue("@username", linfo.username);
q = com.Parameters.AddWithValue("@password", linfo.password);
dr = com.ExecuteReader();
linf = new logininfo();
while (dr.Read())
{
linf.username = dr["username"].ToString();
linf.password = dr["password"].ToString();
}
}
catch (Exception ex)
{
return new logininfo();
}
finally
{
dr.Close();
con.Close();
}
return linf;
}
当我尝试登录时，我发现了一个NullReferenceException ...并且异常是
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.
************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an
object.
at
chitty.App_Code.DAL.SERVICES.loginservice.ViewLoginByUsernameAndPassword
(logininfo linfo)
at chitty.frmlogin.btn_login_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32
clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr
wparam, IntPtr lparam)
************** Loaded Assemblies **************
mscorlib
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
CodeBase: file:///C:/WINDOWS/Microsoft.NET/Framework/v4.0.30319/mscorlib.dll
----------------------------------------
chitty
Assembly Version: 1.0.0.0
Win32 Version: 1.0.0.0
CodeBase: file:///C:/Program%20Files/itek/chittysoft/chitty.exe
----------------------------------------
System.Windows.Forms
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 built by: RTMRel
CodeBase:
file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms
/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 built by: RTMRel
CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/
v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 built by: RTMRel
CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System/
v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Data
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_32/System.Data/
v4.0_4.0.0.0__b77a5c561934e089/System.Data.dll
----------------------------------------
System.Core
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 built by: RTMRel
CodeBase:
file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Core/
v4.0_4.0.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------
System.Configuration
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
CodeBase:
file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Configuration/
v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Xml
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 built by: RTMRel
CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Xml/
v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
System.Transactions
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_32/System.Transactions/
v4.0_4.0.0.0__b77a5c561934e089/System.Transactions.dll
----------------------------------------
System.EnterpriseServices
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
CodeBase:
file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_32/System.EnterpriseServices/
v4.0_4.0.0.0__b03f5f7f11d50a3a/System.EnterpriseServices.dll
----------------------------------------
************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.
For example:
<configuration>
<system.windows.forms jitDebugging="true" />
</configuration>
When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.
我还在app.config中设置了“jitdebugging = true”。但仍然会发生此错误。请为此找到解决方案。
答案 0 :(得分：0)
我想这是因为你试图在finally块中关闭dr，最后块将一直执行，因为它将一直调用。
在打开或创建dr的对象之前可能会出现错误，在该情况下dr可能永远不会被分配或打开，并且您强行关闭它。
尝试在Catch块中移动这些代码而不是最后，或者如果你确定con和dr可用并打开，你可以在try块之外写下这些语句。
finally
{
dr.Close();
con.Close();
}