How to format and modify value in data grid row at run time based on previous row values

Download Sample Project

This was a question was asked by one of my site visitors, Mike. Following is the text of the question:

This is a similar question to one you have already answered in formatting Grid Views. However there are 2 main differences. First: I want to change the value of a column (not the format) in any row if the row preceding it has a certain value in the same column.

This question translates to How do you change value of a data grid column based on values of previous row(s). I generalized this question to cover all previous rows and not just the preceding row. Answer to all such questions relies on handling events like RowDataBound or RowCreated events. When a data grid or grid view renders, RowDataBound fires when row is being data bound and then RowCreated is fired after it has been data bound and row has been created. So depending on at what stage of rendering you want to change behavior of a row, you will subscribe either of these events. In the sample project, I am subscribing to RowDataBound event.

Next step is to access values from previous rows. Here you have choice. One, you can keep some local vaiable that stores values from previous row(s) and then use them in current row event handling. Two, you can access the previous GridRow based on index. In this sample i will discuss the approach of accessing previous row based on index and then extracting values from certain cells.

In RowDataBound event handler, GridViewRowEventArgs provides you access to DataItem associated with current row only. You do not have access to DataItem associated with previous rows. But at this point, previous rows have been prepared for rendering. You have access to all the cell values associated with previous row. You can access GridRow object of previous rows and extract text from cells that you are interested in. In the sample project, I am accessing ListPrice from fourth column and then displaying it in current row along with price associated with current row. Well, this does not sound like something that is very interesting or useful. But it serves the purpose of demonstrating you will accomplish the task.

Here is the code snippet from sample project.

protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
 if (e.Row.RowType == DataControlRowType.DataRow)
 {
  double price = -1.0;
  double prevPrice = -1.0 ;
  // Access the previous row.
  if (e.Row.RowIndex != 0)
  {
   GridViewRow prevRow = this.productsGrid.Rows[e.Row.RowIndex - 1];
   if (null != prevRow && 
    prevRow.RowType == DataControlRowType.DataRow)
   {
    double.TryParse(prevRow.Cells[3].Text, out prevPrice);
   }
  }
  var thisRowData = e.Row.DataItem as DataRowView;
  if (!Convert.IsDBNull(thisRowData["ListPrice"]))
  {
   double.TryParse(thisRowData["ListPrice"].ToString(), out price);
  }
  var ctrl = e.Row.FindControl("prevPriceLabel") as Label;
  if (null != ctrl)
  {
   ctrl.Text = string.Format("{0} - {1}", prevPrice, price);
  }
 }
}

The attached sample project is a VS2010 project. There is no VS2010 or .Net4.0 implementation in the project. So if you are using VS2008 or prior, you should be able to copy the implementation files into your own project.

Feel free to send me any request for any other grid view implementation you would like to be answered or implemented.