Object reference not set to an instance of an object. - asp.net

Question

My codes below don't have any errors during the compile time but when I open the page an error occur at the Guid currentUserId = (Guid)currentUser.ProviderUserKey; stating that Object reference not set to an instance of an object.
foreach(DataRowView ProfileInfo in UserProfileDataSource.Select(DataSourceSelectArguments.Empty))
{
//Some codes where I display data from database
}
protected void UserProfileDataSource_Selecting(object sender, SqlDataSourceSelectingEventArgs e)
{
MembershipUser currentUser = Membership.GetUser();
Guid currentUserId = (Guid)currentUser.ProviderUserKey;
e.Command.Parameters["USERID"].Value = currentUserId;
}
and here is my SQLDataSource
<asp:SqlDataSource ID="UserProfileDataSource" runat="server"
ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
onselecting="UserProfileDataSource_Selecting"
ProviderName="<%$ ConnectionStrings:ConnectionString.ProviderName %>"
SelectCommand="SELECT "TITLE", "FAMILYNAME", "GIVENNAME", "MIDDLENAME", "POSITION", "INSTITUTIONNAME", "USERID", "REGISTEREDDATE" FROM "MEMBERINFO" WHERE ("USERID" = ?)">
<SelectParameters>
<asp:Parameter Name="USERID" Type="Object" />
</SelectParameters>
</asp:SqlDataSource>
Ernie

Answer 1

you should check to make sure that currentUser is not null before trying to access it:
if ( currentUser != null )
{
/* do stuff here */
}
else
{
/* do something else, like show an error message perhaps */
}

Answer 2

try this code:
string username = HttpContext.Current.User.Identity.Name;
if(!string.IsNullOrEmpty(username))
{
MembershipUser currentUser = Membership.GetUser(username);
Guid currentUserId = new Guid(currentUser.ProviderUserKey.ToString());
}

Answer 3

You appear to be allowing anonymous users to access a page that requires a logged in user. You can't get the user if they haven't logged in yet.
Security consists of two parts, authorization and authentication. Authentication is logging in, but authorization is denying access to pages to unauthorized users (such as ones that have not yet logged in, or do not have the correct roles assigned to them).
If your page depends on an authenticated user, then you should deny anonymous users access. If the page does not depend on an authenticated user, but merely makes use of member information if they are authenticated, then you need to guard against calling member functions (or anything that uses member data) if the user is not authenticated.

Answer 4

The issue is Bad code.
Try these steps:-
In your website, set the "Start page" to the correct "login" page.
Once you login, correctly and then land on the page, you should be able to access this property.
You may get into the same error if you click logout button and the landing page might be referring to this membership information.
So the work-around is simple.
1.Set the start page correctly.
2.Handle the 2 cases:- user is logged in and user is not logged in efficiently.
an example is as below:-
protected void Page_Load(object sender, EventArgs e)
{
if (Membership.GetUser() == null)
{ Label1.Text = "";
Label_TotalCoxxxxxxxxx.Text = "";
Label_TotalSuxxxxxxxxx.Text ="";
}
else {
string loggedinuser = Membership.GetUser().ToString();
Label1.Text = loggedinuser;
Label_TotalCoxxxxxxxxx.Text = "Total of xxxxxxxxxx Added in the current Month:-";
Label_TotalSuxxxxxxxxx.Text = "Total of yyyyyyyyyy done in the current Month:-";
}
}