If outside the loginView, the gridview can show correctly!
Put inside Login View and use below code
<LoggedInTemplate>
<asp:GridView ID="GridView1" runat="server">
</asp:GridView>
</LoggedInTemplate>
((GridView)LoginView1.FindControl("GridView1")).DataSource = query;
((GridView)LoginView1.FindControl("GridView1")).DataBind();
Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
Line 22: ((GridView)LoginView1.FindControl("GridView1")).DataSource = query;
How to show GridView inside Login with databind in c#?