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Implementation of paging and sorting for the GridView control that works with an array of objects

, 16 Mar 2007
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The article describes how to implement paging and sorting for the GridView control that works with an array of objects.

Screenshot - gridviewex.gif

Introduction

Fairly often, such a data presentation model is used: an array of objects is bound to a GridView control with predefined columns. This model was popularized by the DotNetNuke web framework and has the advantage of working with the business objects instead of nameless rows of a data table. A classic example:

<asp:GridView id="gv" runat="server" AutoGenerateColumns="False" ...
    <Columns>
        <asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name"  />
        ... 
    </Columns>
</asp:GridView>

and elsewhere in Page_Load:

if (!IsPostBack)
{
    gv.DataSource = someArray;
    gv.DataBind();
}

A pretty good model, in my opinion. But, the GridView control does not have built-in ability for sorting and paging if it is bound to an array of objects. Let's implement it.

The code overview

I inherit my control from the GridView control and override the OnInit method in order to add two event handlers.

this.PageIndexChanging += new GridViewPageEventHandler(BaseGridView_PageIndexChanging);
this.Sorting += new GridViewSortEventHandler(BaseGridView_Sorting);

The paging implementation is trivial.

void BaseGridView_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
     this.PageIndex = e.NewPageIndex;
     BindDataSource();
}

The sorting one is rather complicated. The GridView control has a sorting event handler, but it does not save information about the previous sorting state. So, I added a few variables to save the data: PreviousSortExpression, CurrentSortExpression, and CurrentSortDirection.

void BaseGridView_Sorting(object sender, GridViewSortEventArgs e)
{
      //for unknown reason e.SortExpression always is Ascending
      if (PreviousSortExpression == e.SortExpression)
      {
          e.SortDirection = SortDirection.Descending;
          PreviousSortExpression = null;
      }
      else
          PreviousSortExpression = e.SortExpression;

     CurrentSortExpression = e.SortExpression;
     CurrentSortDirection = e.SortDirection;
     ChangeHeaders(this.HeaderRow);
     BindDataSource();
}

A little something is lacking. There is no visual presentation whether the grid is sorted and how it is sorted. So, I change the sorted column header to show this information. I do it by means of two Unicode symbols: the up arrow (\u25bc) and the down arrow (\u25b2).

private void ChangeHeaders(GridViewRow headerRow)
{
    for (int i = 0; i < headerRow.Cells.Count; i++)
    {
        if (headerRow.Cells[i] is DataControlFieldCell)
        {
            DataControlField field = 
              ((DataControlFieldCell)headerRow.Cells[i]).ContainingField;

            //remove all previous sorting marks if they exist
            Regex r = new Regex(@"\s(\u25bc|\u25b2)");
            field.HeaderText = r.Replace(field.HeaderText, "");

            if (field.SortExpression != null && field.SortExpression == 
                CurrentSortExpression)
            {
                //add current sorting state mark
                if (CurrentSortDirection == SortDirection.Ascending)
                    field.HeaderText += " \u25b2";
                else
                    field.HeaderText += " \u25bc";
            }
        }
    }
}

Now, about filling the grid with data. I add the event that occurs when the data source is requested and the method that will handle this event.

public delegate void DataSourceRequestedEventHandler(out Array dataSource);
public event DataSourceRequestedEventHandler DataSourceRequested;

Refilling of the grid occurs when a user sorts the grid or changes the current page. For initial filling, the BindDataSource method is used.

public void BindDataSource()
{
    Array dataSource = null;
  
    //request for the data source
    if (DataSourceRequested != null)
       DataSourceRequested(out dataSource);
    
    if (dataSource == null)  
       throw new Exception("Failed to get data source.");   

    //sort the data in case of need
    if (CurrentSortExpression != null)
    {
        ArrayList ar = new ArrayList(dataSource);
        ar.Sort(new ArrayComparer(CurrentSortExpression, 
                                  CurrentSortDirection));
        dataSource = ar.ToArray();
    }
   
    base.DataSource = dataSource;
    base.DataBind();
}

ArrayComparer is the implementation of the IComparer interface to compare two objects by a specified property in a specified order (ascending or descending).

How to use it

First of all, because I hide all the paging and sorting functionality inside the new control, I have to reject the old data binding method explicitly. So, I add an event handler for all requests for the data source and the method to call the data binding. And also, it is needed to allow paging and sorting in the GridView Smile | :)

<cc:GridViewEx ID="gv" runat="server" AllowPaging=True AllowSorting=True 
        OnDataSourceRequested="gv_DataSourceRequested" 
        AutoGenerateColumns="False">
    <Columns>
        <asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name"  />
        ... 
    </Columns>>

That is all you need to use this control, no additional work for paging or sorting is required. The full code can be found in the above demo.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Mykola Tarasyuk
Software Developer (Senior)
Ukraine Ukraine
I am a software developer from Ukraine. In my spare time (this means "very rarely last years"), I am blogging about ASP.Net and web development.


Comments and Discussions

 
Questionnative SqlDataSource of Gridview PinmemberCyNETT16-Jul-08 5:48 
How can I use my SqlDataSource1 (defined in .aspx file) which already works with my GridView ?
When I modify my Gridview with your code - exception is thrown: Failed to get data source.
AnswerRe: native SqlDataSource of Gridview PinmemberMykola Tarasyuk16-Jul-08 9:31 
GeneralQuestion Pinmembercontini9-Apr-08 4:47 
GeneralRe: Question [modified] PinmemberMykola Tarasyuk9-Apr-08 7:46 
GeneralRe: Question Pinmembercontini10-Apr-08 0:22 
GeneralRe: Question PinmemberMykola Tarasyuk10-Apr-08 6:04 
GeneralRe: Question Pinmembercontini11-Apr-08 2:31 
GeneralRe: Question PinmemberMykola Tarasyuk11-Apr-08 6:16 
GeneralThanks for the control PinmemberMember 27980349-Mar-08 8:17 
QuestionFancy triangles in compact framework? Pinmemberscoroop3-Aug-07 3:18 
AnswerRe: Fancy triangles in compact framework? PinmemberMykola Tarasyuk3-Aug-07 7:11 
GeneralThanks! [modified] Pinmemberdarshan arney27-Jul-07 7:43 
GeneralSorting on aggregate element. PinmemberMassimo Ugues17-Jul-07 6:04 
AnswerRe: Sorting on aggregate element. PinmemberMykola Tarasyuk18-Jul-07 20:25 
GeneralRe: Sorting on aggregate element. PinmemberMassimo Ugues23-Aug-07 0:19 
QuestionHi' Pinmemberturbochris23-Apr-07 11:28 
AnswerRe: Hi' PinmemberMykola Tarasyuk24-Apr-07 21:56 
GeneralRe: Hi' Pinmemberturbochris25-Apr-07 15:09 
GeneralRe: Hi' PinmemberMykola Tarasyuk25-Apr-07 19:42 
GeneralRe: Hi' PinmemberMykola Tarasyuk27-Apr-07 4:54 

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