DataGrid & The Custom Row Selection

We have one module where you select rows from a grid, then can perform actions on multiple entries. The first column in the grid contains checkboxes. So whatever is ticked is what the actions should apply to. However, if you check the box, it also highlights the row. So there are actually 2 things visually that show the user what is selected.

Clicking anywhere on the row should highlight the row, but since highlighting and the checkbox shows what is selected, then we need some custom code to also check the box when the row is highlighted.

My team had made a tweak to the underlying control, which had broken the checkbox being ticked when the row is selected.

When we recreated the bug, we realised that – because there’s 2 ways of selecting (highlight and checkbox), when you click buttons to perform actions, it actually checks against what is highlighted. So even though we had introduced a bug that it no longer checks the box, it doesn’t actually cause any problems at all because the checkboxes are merely a visual thing.

A simple fix would be to just remove the column since it is redundant. Then a lot of code could be cleaned up.

However, our Product team said that even though multiselect behaviour has always existed, many users weren’t aware and so clicked each checkbox one by one. So it sounds like some users like clicking rows, some like using checkboxes, and some like using keyboard shortcuts.

The keyboard behaviour seemed rather strange too and caused extra complications with the code. You can press down/up which selects/deselect the row below/above the row that is currently focussed. However, there is no visual indicator of which row actually has the focus. Other shortcuts include pressing Spacebar which toggles the checkbox on/off. Pressing ctr+up/down jumps to the top/bottom respectively and checks the box (but if it is already checked, then it doesn’t uncheck it; which is inconsistent with up/down without the Control key). You can also press ctrl+a which selects all rows, but you cannot deselect all rows.

It really illustrates how something basic can be complicated to make all users happy. Then the more custom code you add, the more likely there’s bugs and other inconsistencies.

I was noticing inconsistencies with the shortcuts. So when I had implemented my fix, I was convinced I had broken them.

private void ListData_KeyUp(Object sender, KeyEventArgs e)
{
	if (listData.CurrentCell == null)
		return;
	
	if (e.KeyData == Keys.Down || e.KeyData == Keys.Up)
		HandleGridRowSelection(mouseActionOrSpaceKey: false);
	
	if (e.KeyData == Keys.Space)
	{
		_isSpaceKeyPressOnCheckBox = listData.CurrentCell.ColumnIndex.Equals(_checkBoxColumnIndex);
		HandleGridRowSelection(mouseActionOrSpaceKey: true);
		_isSpaceKeyPressOnCheckBox = false;
	}
	
	if ((e.Modifiers == Keys.Control && (e.KeyCode == Keys.A || e.KeyCode == Keys.Up || e.KeyCode == Keys.Down)))
		HandleCheckBoxHeaderClick(combinationKeys: true);
}

I thought I had broken the functionality because sometimes I saw it highlight all rows but it didn’t select the checkbox. Then when I was looking at the code again (which I hadn’t modified), I noticed it was called from Key Up. The ListData_KeyUp code would expect you to let go of A whilst still holding down Control. Although most people would do that due to their hand positioning, sometimes I was finding I was basically “stabbing” the keys so was releasing them roughly the same time. So in the times I had actually released Control first, then the IF statement doesn’t pass and therefore the checkboxes aren’t selected. I think the standard implementation is to check OnKeyDown and not UP.