Web Forms :: Code-Behind Null Reference Exception Accessing Controls With Derived PageBase?
Feb 16, 2010
I have a class that derives from System.Web.UI.Page and have set my pages to derive from this custom page class instead of Page. At runtime, the controls are never initialized and throw a NullReferenceException. I've changed some class names and namespaces in the pasted code to protect the innocent. The only thing that I currently override in my PageBase is OnPreLoad and I do call the base.OnPreLoad. I'll eventually add more functionality to this PageBase but for now all that it has is this:
[Code]....
I've tried putting this into a class library (with System.Web referenced) and I've also tried moving the class into the web application and had the same results either way. As another strange twist, I have another class with derives from PageBase called IndexPageBase and it doesn't have this problem:
[Code]....
[Code]....
[Code]....
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i have null reference exception in grid view, in the
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the full code :
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Dec 10, 2010
I am getting the Null reference exception in
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also when I used the Quickwatch, I get this error message.
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Jul 9, 2012
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protected void ImageButton2_Click1(object sender, ImageClickEventArgs e)
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Jan 20, 2011
I have a .ascx file residing in another page which has a button on it. On click I run a select statement that accesses the textbox for a value.
However, it keeps returning a Null Exception Error. I am trying access the textbox and its text through
[Code]....
I also tried -[Code]....
I also tried -[Code]....
But none of them work. Please can someone advise me how I find the textbox and then access its text?I have looked round the forums / google and cant find a way of doing this!
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Dec 15, 2010
let me see if I can explain this clearly. I have a gridview control
and I am trying to use the Edit function. In my gridview, there are numerous rows. I pick one to change and click Edit. I then see the boss name in my gridview and click "Change". When I click Change, I'm expecting two fields to appear, one is a label, the other is a DropDownList. I get this error when I click:
System.NullReferenceException was unhandled by user code
Message=Object reference not set to an instance of an object.
Source=App_Web_lzmklgbg
StackTrace:
at Training_TRManageOrg.LinkButton1_Click(Object sender, EventArgs e) in d:projectsediting.aspx.cs:line 108
at System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e)
at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument)
at System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument)
at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)
at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
InnerException:
Gridview HTML:
<asp:TemplateField HeaderText="Director">
<EditItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("director") %>'></asp:Label>
<asp:LinkButton ID="LinkButton1" runat="server" OnClick="LinkButton1_Click">Change</asp:LinkButton>
<asp:Label ID="Label4" runat="server" Text="Director" Visible="False"></asp:Label>
-
<asp:DropDownList ID="DropDownList2" runat="server" DataSourceID="trDirector"
DataTextField="name" DataValueField="id" onselectedindexchanged="DropDownList2_SelectedIndexChanged"
Visible="False"></asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("director") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
Code Behind:
protected void LinkButton1_Click(object sender, EventArgs e)
{
DropDownList DropDownList1 = ((DropDownList)FindControl("DropDownList1"));
DropDownList1.Visible = true; // this line is where the exception occurs
Label3.Visible = true;
}
I figure I must be overlooking something so I'm asking what am I missing?
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Oct 19, 2010
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Aug 20, 2010
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[Code]....
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[Code]....
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[Code]....
Here is the view code:
[Code]...
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My controller calls a class in my model which is getting data from a REST web service. The class in the model then passes the data back to the controller using an IList, like so:
[Code]....
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[Code]....
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[Code]....
[Code]....
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PageBase:
public abstract class PageBase : ClientSidePageBase
{
public WebMessage Message
{
get
[code]...
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Security Exception:
Description:
The application attempted to perform an operation not allowed by the security policy. To grant this application the required permission contact your system administrator or change the application's trust level in the configuration file.
Exception Details: System.Security.SecurityException:
System.Security.Permissions.SecurityPermission
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Nov 15, 2010
In a recent post, I expressed a need to access the properties for the body using declarative syntax, see
Contentplaceholder for replacing attributes?
But, the syntax confuses the editor which is not acceptable.
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Oct 27, 2010
I have a GridView with the following columns
<asp:TemplateField HeaderText="Name">
<FooterTemplate>
<asp:TextBox ID="txt_Name" runat="server"></asp:TextBox>
</FooterTemplate>
<ItemTemplate>
<asp:Label ID="lbl_name" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "t_Name") %>' />
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<EditItemTemplate>
<asp:TextBox ID="txt_name" runat="server" Width="100px" Text='<%#DataBinder.Eval(Container.DataItem,"t_Name") %>'></asp:TextBox>
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</asp:TemplateField>
<asp:TemplateField HeaderText="Created By">
<ItemTemplate>
<asp:Label ID="lbl_tabcreatedby" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "t_CreatedBy") %>' />
</ItemTemplate>
</asp:TemplateField>
<asp:CommandField HeaderText="Modify" ShowEditButton="True" />
<asp:CommandField HeaderText="Delete" ShowDeleteButton="True" />
<asp:TemplateField HeaderText="Add a New Name">
<FooterTemplate>
<asp:LinkButton ID="lnkbtn_AddName" runat="server" CommandName="Insert">Add Name</asp:LinkButton>
</FooterTemplate>
</asp:TemplateField>
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protected void gv_Name_RowCommand(object sender, GridViewCommandEventArgs e)
{
string t_Name = ((TextBox)(gv_Name.FooterRow.FindControl("txt_Name"))).Text;
// Insert Code
}
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However I can get the text if I disable the ViewState for the page.
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Jan 16, 2010
I downloaded a sample Rolodex from here: [URL] the file to download is at the bottom of the page and it is called 'RolodexDatalist.zip (6.71 kb)' So I changed the HTML to it points to my SQL Server DB. I changed the ConnectionString to this:
<connectionStrings>
<add name="CustomersConnectionString" connectionString="Data Source=EXCEL-4J2W8KYNPSQLEXPRESS;Initial Catalog=Customers;Integrated Security=True"
providerName="System.Data.SqlClient" />
</connectionStrings>
Now, everything points to my DB! I thought, ok great, this should be pretty easy. However, when I debug, I get this error message: 'Null reference was unhandled by user code. Object reference not set to instance of an object. Troubleshooting Tips: use the "new" keyword to set an instance of an object.' This line is yellow:
Dim conStr As String = ConfigurationManager _
.ConnectionStrings("conStr").ConnectionString
Here is the code-behind:
Imports System.Data
Imports System.Data.SqlClient
Imports System.Collections.Generic
Partial Class VB
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
If Not IsPostBack Then
ViewState("CurrentAlphabet") = "ALL"
Me.GenerateAlphabets()
Me.BindDataList()
End If
End Sub
Private Sub BindDataList()
Dim conStr As String = ConfigurationManager _
.ConnectionStrings("conStr").ConnectionString
Dim con As New SqlConnection(conStr)
Dim cmd As New SqlCommand("spx_GetContacts")
cmd.Connection = con
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.AddWithValue("@Alphabet", ViewState("CurrentAlphabet"))
con.Open()
dlContacts.DataSource = cmd.ExecuteReader()
dlContacts.DataBind()
con.Close()
If ViewState("CurrentAlphabet").ToString().Equals("ALL") Then
lblView.Text = "all Contacts."
Else
lblView.Text = "Contacts whose name starts with " & _
ViewState("CurrentAlphabet").ToString()
End If
End Sub
Private Sub GenerateAlphabets()
Dim alphabets As New List(Of Alphabet)()
Dim alphabet As New Alphabet()
alphabet.Value = "ALL"
alphabet.isNotSelected = Not alphabet.Value _
.Equals(ViewState("CurrentAlphabet"))
alphabets.Add(alphabet)
For i As Integer = 65 To 90
alphabet = New Alphabet()
alphabet.Value = [Char].ConvertFromUtf32(i)
alphabet.isNotSelected = Not alphabet.Value _
.Equals(ViewState("CurrentAlphabet"))
alphabets.Add(alphabet)
Next
rptAlphabets.DataSource = alphabets
rptAlphabets.DataBind()
End Sub
Protected Sub Alphabet_Click(ByVal sender As Object, ByVal e As EventArgs)
Dim lnkAlphabet As LinkButton = DirectCast(sender, LinkButton)
ViewState("CurrentAlphabet") = lnkAlphabet.Text
Me.GenerateAlphabets()
Me.BindDataList()
End Sub
End Class
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Nov 24, 2010
I have created one itemtemplate to display one button in subgrid(grid in grid) in .ascx page:
<asp:datagrid id="grid1" runat="server>
<columns>
<asp:TemplateColumn HeaderText="Close Manually" ItemStyle-HorizontalAlign="left">
[code]...
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