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

• Download gridviewex.zip - 10.6 KB

Introduction

Fairly often the such data presentation model is used: the array of objects is bound to the GridView control with the predefined columns. Its model is popularized by the DotNetNuke web framework and has the advantage of work with the business objects instead of the nameless rows of the 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 build-in ability for sorting and paging if it is bound to the array of the 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 sorting event handler but it does not save information about previous sorting state. So I add a few variables to save the data: PreviousSortExpression, CurrentSortExpression, 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 someting is lacking. There is none visual presentation whether grid is sorted and how it is sorted. So I change sorted column header to show this information. I do it by the 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 of 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 user sorts grid or changes the current page of the data. 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 specified property in specified order(Ascending or Descending).

How to use it

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

<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 that you need to use this control, no additional work for paging or sorting use is required.
The full code you can find in the above demo.