The ASP.NET GridView allows for a row of data to be edited by setting the EditIndex property of the GridView, placing the entire row in edit mode.
You may not want the entire row in edit mode if you are using DropDownList controls for several columns in the EditItemTemplate. If each DropDownList has many options then loading them all at once may result in a sluggish page. Also, if your data structure is more like a 2 dimensional array rather than a set of rows, you may want to edit each cell individually.
Here I will demonstrate how to achieve this and also how to deal with event validation without disabling it.
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