Filtering results in ASP.NET Web Forms

Question

I'm trying to walk through a tutorial on web forms, and my attempts to filter search results isn't working quite right:

The contents of the asp page look like this:

<form id="form1" runat="server">

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="button1" runat="server" onclick="button1_Click" Text="Submit" />
<asp:GridView ID="GridView1" AllowPaging="true" PageSize="8" AutoGenerateColumns="false" runat="server"
OnPageIndexChanging="GridView1_PageIndexChanging">

   <Columns>
      <asp:BoundField HeaderText="Qual ID" DataField="ID" />
      <asp:BoundField HeaderText="Client Name" DataField="Client_Name" />
      <asp:BoundField HeaderText="Project" DataField="Project_Name" />
      <asp:BoundField HeaderText="Uploaded By" DataField="Uploaded_By" />
   </Columns>

</asp:GridView>
</form>

And the code behind file:

public partial class Sample1 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

    SourceDataContext db = new SourceDataContext();

    GridView1.DataSource = from q in db.Cust
                           orderby q.ID
                           select q;
    GridView1.DataBind();
}

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.PageIndex = e.NewPageIndex;

    GridView1.DataBind();
}
protected void button1_Click(object sender, EventArgs e)
{
    string client = TextBox1.Text;

    SourceDataContext db = new SourceDataContext();

    GridView1.DataSource = from q in db.Cust
                           where q.Client_Name == client
                           orderby q.ID
                           select q;
    GridView1.DataBind();

}
}

The filtering works, although it the paging stops working. Any suggestions appreciated.

Thanks.

Answer 1

Issue 1: This should only run on GET requests. ViewState will take over on PostBacks and populate the grid.

protected void Page_Load(object sender, EventArgs e) 
{ 
    if(!this.Page.IsPostback)
    {
        SourceDataContext db = new SourceDataContext(); 

        GridView1.DataSource = from q in db.Cust 
                               orderby q.ID 
                               select q; 
        GridView1.DataBind(); 
    }
}

Issue 2: You need to reset the page index because the recordset changed. The current page may not exist.

protected void button1_Click(object sender, EventArgs e)      
{      
    string client = TextBox1.Text;      

    SourceDataContext db = new SourceDataContext();      

    GridView1.DataSource = from q in db.Cust      
                           where q.Client_Name == client      
                           orderby q.ID      
                           select q;      
    GridView1.DataBind();    

    GridView1.PageIndex = 0;

}   

Issue 3: You're calling DataBind(), but not setting a new datasource.

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)              
{              
    GridView1.PageIndex = e.NewPageIndex;                         
} 

Also,

consider caching the recordset and filtering that instead of making a call to the server for a new recordset, however, this depends on "need". Caching a recordset will not find any new records obviously, which may not fit your business need.

consider setting your events in Code Behind in the OnInit method:

protected void Page_Init(object sender, EventArgs e) 
{
    this.GridView1.PageIndexChanging += GridView1_PageIndexChanging;
}

Answer 2

it seems to me that there are two problems

1. on Page_Load enclose binding in !IsPostBack
2. GridView1_PageIndexChanging do not bind again
3. see the catch by Chris Gessler

Code

public partial class Sample1 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
    if(!IsPostBack)  
    {

    SourceDataContext db = new SourceDataContext();

    GridView1.DataSource = from q in db.Cust
                           orderby q.ID
                           select q;
    GridView1.DataBind();
   }
}

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.PageIndex = e.NewPageIndex;


}
protected void button1_Click(object sender, EventArgs e)
{
    string client = TextBox1.Text;

    SourceDataContext db = new SourceDataContext();

    GridView1.DataSource = from q in db.Cust
                           where q.Client_Name == client
                           orderby q.ID
                           select q;
    GridView1.DataBind();
    GridView1.PageIndex = 0;

}
}