Repeater (Lists)

Repeater keeps one Component and ViewModel alive for each item of a list Signal, matched by a key. It does the add and remove bookkeeping that instantiate and Component.remove() otherwise need by hand. Its signature is in the Python API.

from tesserae import Repeater, Signal

items = Signal([])  # the single source of truth

repeater = Repeater(view, items, "Card_View.yaml", CardViewModel, container)

# in a project, a name is enough: Views/Card_View.yaml and CardViewModel (ViewModels/Card_ViewModel.py)
repeater = Repeater(view, items, "Card", into=container)

items.update(lambda lst: [*lst, new_id])               # adds one
items.update(lambda lst: [i for i in lst if i != id])  # removes one

Argument	Default	Use
viewmodel_cls	found by the view's name	the ViewModel class; left out, it is NameViewModel in Name_ViewModel.py, beside the view or in the project's ViewModels/
key	the item itself	for items that are dicts or dataclasses: a function returning a stable, hashable key
args	lambda item: (item,)	what is forwarded to viewmodel_cls(component, *args): override it for a ViewModel that needs more than the item

examples/todo_list/ in the repository forwards the shared items Signal too, so an item can remove itself.

What it does and doesn't do

Repeater adds or removes instances to match the set of keys present:

• It never reorders an instance that is already there. The engine's tree has no child-reorder operation.
• It never re-applies a changed item's data to an existing instance. An item's mutable fields belong to that item's own ViewModel, through its own Signals. Repeater only asks which keys are present.

Repeater.remove() tears every remaining instance down and unsubscribes, the way Component.remove() does.

Iterating

len(repeater)               # how many instances are alive
for key, component, vm in repeater:
    ...
repeater[key]               # (component, viewmodel) for one key

In a scrolling list

Put the container the Repeater fills inside a ScrollView: see Layout.