Toggling Item State

We have the ability to add items, but now we need to extend their functionality to allow for indicating that a particular item has been completed. We also want the ability to “reset” the completion state of a particular checklist.

Add the ability to toggle to the service

We will start with allowing a particular item in a checklist to be toggled between checked/unchecked.

The approach here will be the same as any other state change we would approach. Generally, we want to:

1. Add a source for the action that will be nexted
2. Subscribe to that source
3. Have the reducer update the state signal

The reducer for this one is actually a bit tricky, but go ahead and see how much of this you can implement on your own in the ChecklistItemService.

Add the following source to ChecklistItemService:

  toggle$ = new Subject<RemoveChecklistItem>();

It might strike you as a bit odd that the type is RemoveChecklistItem that it just because the toggle needs the same information — just the id of the item being toggled.

Add the following reducer:

    this.toggle$.pipe(takeUntilDestroyed()).subscribe((checklistItemId) =>
      this.state.update((state) => ({
        ...state,
        checklistItems: state.checklistItems.map((item) =>
          item.id === checklistItemId
            ? { ...item, checked: !item.checked }
            : item
        ),
      }))
    );

There is nothing new going on here — although the reducer step looks a little complex, the basic idea is that to overwrite the old checklistItems it maps through all of them and if it finds one matching the given checklistItemId it will toggle its checked value.

NOTE: Technically right now we do not need to spread the existing ...state as checklistItems is the only property on the state. However, I will always spread the previous state by default as it is likely at some point that more properties will be added to the state (and, in fact, we will be doing that later for this particular service).

Add a checkbox to the checklist item

Now that we have support for toggling an item in the service, we just need to interact with it.

Add the following output to ChecklistItemListComponent:

  @Output() toggle = new EventEmitter<RemoveChecklistItem>();

Add a toggle button to the template of the ChecklistItemListComponent: