MatSelectionList should update option selection state when list of options changes

[benelliott]

What is the expected behavior?

MatSelectionList should update option selection state when list of options changes

What is the current behavior?

If you change the list of options after the view has been initialised, MatSelectionList does not update the model of the new options to reflect that they are selected in the model.

What are the steps to reproduce?

https://stackblitz.com/edit/angular-material2-issue-ptk4tc?file=app/app.component.ts

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Latest StackBlitz template

Is there anything else we should know?

MatSelectionList should listen to options.changes on the options QueryList:

components/src/material/list/selection-list.ts

Line 323 in fc0b971

@ContentChildren(MatListOption, {descendants: true}) options: QueryList<MatListOption>;

This is how MatSelect works:

components/src/material/select/select.ts

Line 550 in 9eeb4b5

this.options.changes.pipe(startWith(null), takeUntil(this._destroy)).subscribe(() => {

[benelliott]

One problem is that MatSelectionList does not internally keep track of its selection state - instead it delegates this to each corresponding option item (except for _tempValues which is only used for initialisation). I think that to fix this bug we would need to introduce a longer-lived version of _tempValues that can be consulted whenever an option item is added.

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