mat-selection-list: selectAll and deselectAll methods should trigger selectionChange event

selectAll() and deselectAll() methods on MatSelectionList should automatically trigger the selectionChange event.

What is the use-case or motivation for this proposal?

Select some documents from a list.

The MatListOptions have [value] populated with an object containing a number of properties of the document (name, file size, last edited date, expiry date, etc.). You want to communicate a warning to the user that specifies the number of expired documents in their current selection. It’s easy enough to calculate the number of expired documents in the current selection when the selectionChange event is fired, but if the user decides to selectAll, this event is not triggered, so additional workarounds need to be made to cover this case.

Is there anything else we should know?

[despian]

What if you have a user interaction wired up to selectAll/deselectAll?

I think it would be nice to have the option to trigger this event without having to write extra code.

How about an optional extra parameter to the selectAll and deselectAll methods which would fire the event?

E.g.

selectAll(fireSelectionChange: boolean = false): void {
  ...
}

[jelbourn]

Seeing this now- I believe we should emit the event when the change comes from the user pressing Ctrl + A to trigger the select-all / deselect-all (but not when it happens programatically).