I have made a GroupingView that has a checkbox in the group header to check all rows in that group. Of course you need to be using CheckboxSelectionModel with this. If you check it, it will select all the rows in that group and will collapse the group (configurable). That was easy...
I wanted something more, not all rows in a group are going to always be checked or unchecked. There may be a couple that are checked and a couple that are unchecked so I needed a 3rd state to the checkbox. Say your group has 5 rows and you check 3 of them, the checkbox in the group header shouldn't show the check in the checkbox but it shouldn't show nothing in the checkbox. I now have a "some" check state!
The repo I have on GitHub has a full demo of this. All you have to do is change the path to Ext JS 3.
GitHub repo: https://github.com/mitchellsimoens/E...oxGroupingView
Will take pictures in a little bit.