Added MultiSelect

[wogus3602]

2023-02-09.3.06.19.mov

[ZofiaBernadetta]

Hi @wogus3602 👋

Thanks for the taking the time to work on this! I was playing around with the example app and I noticed a couple of issues.

• The first time I click on a row, the row is highlighted and then immediately goes back to normal. The first selection is not being registered.
• Multiple selection does not work with drag and drop.

You can see both the issues on the screen recording:

Screen.Recording.2023-02-13.at.21.11.08.mov

[RCCoop]

@ZofiaBernadetta , the multi-select not working with drag & drop is something I can work on, since it's my code that ignored the possibility of multiple dragged items. Maybe once @wogus3602 is done with everything else on this PR, I can take that responsibility last :-)

[brendand]

@RCCoop did you ever add support for multi-select drag & drop?

[RCCoop]

@brendand , I haven't, sorry. I've been working on other projects lately that don't use OutlineView, so I haven't had time to look at it.

[tt-tsquared]

I don't think the updated code is correct for multiple selected items. I grabbed your code for an app I'm working on and besides renaming it selectRows my current code is:
func selectRows(
for items: [OutlineViewItem],
in outlineView: NSOutlineView
) {
// Returns -1 if row is not found.
let indices = items.compactMap { outlineView.row(forItem: $0) == -1 ? nil : outlineView.row(forItem: $0) }
outlineView.selectRowIndexes(IndexSet(indices), byExtendingSelection: false)
}

[tt-tsquared]

To get selectionChanged(xxx) to be called when I chose a new outline row I had to comment out some of your code. The first check for isEmpty shouldn't be needed because selectionChanged(emptySet) still needs to be called if you unselect every row. Also returning early because selectedItems and newSelection counts are same caused single selecting new items to not call selectionChanged(xxx) too. Also wasn't sure why the if selectedItems.allSatisfy call was there too?
Current code I'm using:
func outlineViewSelectionDidChange(_ notification: Notification) {
let outlineView = notification.object as! NSOutlineView
let selectedRowIndexes = outlineView.selectedRowIndexes

#warning("Check with original author why commented out code was needed")
//if !selectedRowIndexes.isEmpty {
let newSelections = selectedRowIndexes.compactMap {
outlineView.item(atRow: $0).map(typedItem)
}

// if selectedItems.count == newSelections.count {
// return
// }

        //if selectedItems.allSatisfy({ newSelections.contains($0) }) {
            selectedItems = newSelections
            selectionChanged(Set(selectedItems.map(\.value)))
        //}
    //}
}