It is easy to implement single column sort using ASP.NET DataGrid. Using Sort
functionality in DataView class, data can be sorted correctly with specific
data-type (integer, string, date etc). In this article I will show some simple
techniques to extend sort functionality for multi-column sort. With this feature,
user should be able to sort the data using multiple column selection.
Objectives
Support default sort, single-column sort with Ascending/Descending toggle and
multi-column sort using ASP.NET DataGrid control.
Sample Code
Sample code is attached with this article. Feel free to use it or modify it
depending on your requirement. Sample code provided is not of production
quality and demonstrating multi-column sort is main focus of the sample.
Topics covered
Developing multi-column sort functionality is the main topic in this article.
Basic sorting functionality in DataGrid, DataSet support for XML and some code
re-use techniques are also covered briefly.
Steps involved in supporting Single-column Sort
Using VS .net, On DataGrid properties window, select 'AllowSorting=True'
Using VS .net, On DataGrid properties window click on 'Events' icon and enter event handler name against 'SortCommand'. This will trigger VS .net to create an event handler for sort.
In HTML view of .aspx page, for the columns that require sorting, in the column header add Xml attribute "SortExpression". Value for sort expression should normally be equal to "DataField" attribute value.
ASP.NET highlights the columns that have 'SortExpression', with an underline in column-heading. User can invoke sort on any column by clicking the column header link.
In "SortCommand" event hanlder provide sorting code by re-creating DataSet and applying sort (With the support of DataView.Sort)
Bind DataView to DataGrid.DataSource' property and call 'DataBind' method of DataGrid.
Supporting Multi-Column Sort
There are many ways multi-column sort can be implemented. Approach in this article is based
on the tricks we already know for supporting single column sort.
DataGrid's Sort event handler is called for every column that defines 'SortExpression'. Event object passed in this event handler has property "SortExpression". This will have the sort expression for the column that user clicked.
Assuming that SortExpression property is always unique for each column in DataGrid, it is easy to find current column on which user selected Sort.
Set DataGrid current column's SortExpression to next in the order (Sort on each column is flagged as "ASC, DESC, No sort") and perform sort with current selection.
Till this point most of the logic is similar to single-column sort.
Provide a 'multi-sort' button to explicitly invoke multi-sort. On the event handler of this button, check for 'SortExpression' for each column (Expression should have 'ASC' or 'DESC') and concatenate them to prepare single sort expression.
Use final sort expression with DataView to sort data.
Bind DataView to DataGrid.
DataGrid: Loading data from XML vs. Database
In this sample for simplicity I have loaded DataSet from XML file. DataSet can take data from
any data source using ADO.NET. How and where to get data is not relevant in this example.
There is no technical reason of using one over other and approach might vary from application
to application.
Fig. 1 Shows sample employee data in XML file. DataSet.ReadXML method can
load XML data. DataGrid.DataSource property is used to bind DataSet through DataView.
(DataView class is used to do actual sorting of the data)
Fig. 1: Employee data from "EmpData.xml"
Code Re-use and Code-behind Programming
ASP.NET code-behind is powerful concept and it separates presentation and business logic
for any web page. When we develop any ASP.NET page we need to keep this in mind and avoid
using presentation logic in C# code wherever possible. Code-behind is not everything behind
(I mean presentation logic goes in .aspx page and business logic or complex page handling
logic goes in C# code). Also in this sample I have externalized multi-column sort code
to separate class. This way we can build once and re-use it in many other applications.
Ideally we should have WebUtils (as an example) assembly where all re-usable code for
the projects should reside.
Fig. 2 Shows sample web page showing multi-column sort.
Fig. 2: Sample - Multi Column Sort using ASP.NET DataGrid
Using IIS Management Console, create new virtual directory "MultiSortGrid" and for physical path, select 'MultiSortGrid' folder from the extracted files (Step 1 above).
In your browser type in the URL http://localhost/MultiSortGrid/SortData.aspx
Sort Type Toggle (ASC/DESC): Each time a column is clicked, "Sort type" for that column is toggled in following order: ASC, DESC, No Sort (Clear Sort). User will see the "Sort Type" in column heading text. If there is no "ASC" or "DESC" shown for any column then that column will not be included on multi-column sort. This gives user a better option of what columns should be selected for multi-column sort.
Single column sort (ASC vs. DESC): Click on any column header and DataGrid should show how data is sorted. If column label has "ASC" that means data is sorted ascending order, if column header has "(DESC)" then data is sorted in descending order. If no information is displayed next to column header then current sorting is cleared on this column and this column will not participate in multi-sort.
Multi-Column Sort: Click on each column to select "(ASC)" OR "(DESC)" OR nothing (No sort). Then click on the button that says 'Multi-Sort'. User should see the data sorted as per "ASC/DESC" designation specified in column heading.
Default sort order: Click on button that says "Default" to resent sorting order, back to default.
About the Author
Jayram Tallamraju is a Software Architect/ Sr. Programmer Analyst for Bisys Hedge
Fund Services in Boston, MA. He is MCP of .net, MCSD (Microsoft Certified Solution
Developer) and SCJD (Sun Certified Java Developer). Jay holds an MS in Electronics
and has been working in the software industry for around 10 years. He is focused
more in building server architecture and in building reusable business components.
His current area of expertise is in Microsoft technologies such as .NET, C#, Web
services, ASP.NET, VC++/VB, COM/DCOM, ASP/IIS.
