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asp.net c# gridview label value disappear when sorting

I have a gridview that contain label, the value of this label is assigned in code behind,
I enabled sorting in my gridview and when I click the header to sort the value of the label disappear but the other DataFields doesnt.
<asp:TemplateField HeaderText="<%$Resources:mj.resource, req_category%>" SortExpression="category_id">
<ItemTemplate>
<asp:Label ID="category_id" runat="server"></asp:Label>
</ItemTemplate>
</asp:TemplateField>

Have you set EnableViewState="false" on the GridView or at the page level?
Are you using DataSourceControl (like SqlDataSource) to bind data to the GridView?
If so, you'd have to manually sort and bind data again in the Sorting event.

Hyperlink in datagrid

I am inserting record in datagrid by binding it with data table and I had set autogenerate field ON for datagrid. Now all I want is first column which will comes in datagrid should be hyperlink field and when I will click on link it should redirect to another page. Please help

do like :
<ItemTemplate>
<asp:HyperLink ID="Edit" runat="server" Text="Edit" NavigateUrl='<%# Eval("DataKeyName", "~/View.aspx?Id={0}") %>' />
</ItemTemplate>
Edit:
You need to change the column type to a Hyperlink column.
and where to set is your job Sandesh
<Columns>
<asp:hyperlinkfield headertext="NewsHeadline"
datatextfield="NewsHeadline"
datanavigateurlfield="NewsURL"
datanavigateurlformatstring="http://{0}" />
</Columns>

how to add a link button in the grid view by visual studio?

I want to add a link button in grid view that will navigate to the next form in the website. but i want to know how to insert that button into the grid view column? please help me..

You can add Link buttons in the Item template of a gridview.
<asp:TemplateField>
<ItemTemplate>
<asp:LinkButton ID="Link" runat="server" PostBackUrl="MyNextPage.aspx">Edit</asp:LinkButton>
</ItemTemplate>
</asp:TemplateField>

<Columns>
<asp:TemplateField>
<HeaderTemplate>
// TEXT FOR COLUMN NAME
</HeaderTemplate>
<ItemTemplate>
// ADD LINK BUTTON HERE.
</ItemTemplate>
</asp:TemplateField>
</Columns>
Add this inside grid view.

try this
<asp:GridView ID="GridView1" runat="server">
<Columns>
<asp:ButtonField ButtonType="Link" HeaderText="LinkButton"/>
</Columns>
</asp:GridView>

Make Sure your GridViews datasource is bound. Set Auto-Generate Columns to false.
Open GridViewTask , add new column with Hyperlink Field proper name and path . You are done.

How to set focus on last row of grid

I need to set focus on the last row of the grid after a grid row updation takes place. Can anyone help me out on this?
Below is my gridview,
<asp:GridView ID="grdViewForComment" runat="server" OnRowDataBound="Row_DataBound" AutoGenerateColumns="false">
<Columns>
<asp:TemplateField HeaderText="Advanced search">
<ItemTemplate>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>

Check adding below code
grdViewForComment.Rows[19].Focus(); // RowIndex here.
grdViewForComment.Rows.Count-1

Binding a Button to a GridView

This a pretty simple question, I'm just not sure how to do it exactly. I would like to bind a Button or perhaps ImageButton to a GridView in ASP.NET/C#. Currently, the GridView has two columns and is bound to a DataTable with two columns. I want to add a third column to the GridView, which will include the Button.
I know GridView has ButtonField, but I'm not too sure how to go about using it to do what I want. I want to dynamically generate these Buttons and add them to the GridView.
Here is how my GridView looks right now:
<asp:GridView
ID="GridView1"
Runat="server">
<Columns>
<asp:HyperLinkField
HeaderText="Display Name"
DataNavigateUrlFields="DISPNAME"
DataNavigateUrlFormatString="ViewItem.aspx"
DataTextField="DISPNAME">
<ItemStyle Width="70%" />
</asp:HyperLinkField>
<asp:BoundField
DataField="TypeDisp"
HeaderText="Type">
<ItemStyle Width="20%" />
</asp:BoundField>
</Columns>
</asp:GridView>

You can use a template field like the following,
<TemplateField>
<ItemTemplate>
<asp:ImageButton ImageUrl="image url" CommandName="SomeCommand" CommandArgument='<%# Eval("Id") %>'/>
</ItemTemplate>
</TemplateField>
Then you can handle the RowCommand event of the GridView and check the e.CommandName to see what command to be executed and you can get the e.CommandArgument as well which could be the row Id like I used in the code above.

If we are talking a button that's always present, you can use ButtonField, or even use a TemplateField and provide the template with the button, and bind the data to the button (sounds like you may want to bind data to the attributes of the button?)
If you are looking to dynamically generate buttons in the UI, tap into the RowCreated event and add the button the GridView. You'd have to do this on every page load; the GridView won't remember a button created programmatically.
HTH.