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DataGridView SelectionChanged event behaves strange

Mar 23, 2009 archive

In this post, we’ll look at how the DataGridView SelectionChanged event can behave strange and how to fix it if it does.

In a project, I use a DataGridView to bind data to a grid view. I then listen for its SelectionChanged event and configure other controls according to the data in the grid. For instance, I may disable a move down button if the grid has less than two items or if the selected row is the last one.

However, the SelectionChanged event behaves strange. It fires several times when data is being bound and when the control is displayed. The last time it fires, the RowCount property of the grid is 1, no matter how many rows it contains. This makes my enable/disable functionality fail.

This behavior can be recreated like:

  • Add a DataGridView to a form.
  • Bind its SelectionChanged event and set a local integer to its RowCount.
  • Add a breakpoint to the SelectionChanged event, so it can be inspected.
  • In the form constructor, create a List<String> with several strings and bind it to the grid.
  • Run the application.

As you probably will see, the SelectionChanged event fires several times. The last time it fires, it’s said to contain 1 row, although it has several. Furthermore, the SelectionChanged event also doesn’t fire when the list goes from containing no items to one item, nor from containing one item to no items.

For the data binding, I found the DataSourceChanged event to behave much more stable. It fires every time I modify the data source and fires correctly. For the move up/down functionality, I listen for the CurrentCellChanged event.

After some further issues with SelectionChanged, I found that it also applies to the CurrentCell property as well. If the control has not yet been displayed, this property will be null.

Therefore, when you need to update the GUI according to DataGridView events, follow this pattern:

  1. Create a function that enables and disabled your GUI controls correctly.
  2. Create an event handler that executes this function.
  3. Bind the event handler to the following events of the grid view:
  • CurrentCellChanged
  • DataSourceChanged
  • VisibleChanged

This will hopefully make your GUI behave the way you want it to.