The other day I was trying to figure out why the ItemCommand associated with an ImageButton in a DataGrid had stopped firing and was surprised by why...

Here is the grid in action:

When I clicked on any of the ImageButtons in the grid, the page did post back, but the ItemCommand didn't fire. I experimented with binding the grid at different points in the page lifecycle, but that didn't help. I also tried switching from a DataGrid to a GridView, thinking such a drastic change might get rid of whatever oddity was going on. No such luck.

Finally, I noticed that the grid attribute EnableViewState was false. Originally, this grid had contained some template items with editable content, including text boxes, drop down lists and checkboxes, and ViewState was turned on. But I replaced that functionality with some client side logic using JavaScript and JSON web service calls, so I figured no viewstate was needed any more, and had turned it off. It wasn't until a few weeks later when someone clicked on these image buttons that the problem showed up.

So, long story short, I changed EnableViewState to true, and voila, it started to work again. It beats me why viewstate is needed for a command event to fire when an image is clicked (I could see the image.x and image.y variables in the postback even when it was turned off), somehow the event bubbling from the image click to the containing DataGrid's ItemCommand handler (RowCommand in the GridView) is dependant on viewstate being turned on. If anyone knows why I am all ears!