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Collection Binders

Binders that show ViewModel collections as lists of UI elements.

Overview​

BinderPurpose
ViewModelObservableListBinderDynamic list with a View factory
ViewModelCollectionBinder<T>Static collection (fixed Views)
ViewModelObservableDictionaryBinderDictionary with a View factory
VirtualizedListItemSourceBinderData source for a VirtualizedList

ViewModelObservableListBinder​

The main binder for showing an ObservableList<IViewModel>. Creates and destroys Views as items are added and removed.

How it works​

ObservableList<IViewModel> (ViewModel)
    → ViewModelObservableListBinder
        → IViewFactory.Create(viewModel) on Add
        → IViewFactory.Release(view) on Remove

Inspector properties​

PropertyTypeDescription
FactoryIViewFactory<MonoView>Factory that creates Views (PrefabViewFactory or PrefabViewPool)
FilterICollectionFilter<IViewModel>Optional filter
OrderICollectionOrder<IViewModel>Optional ordering

Mode​

OneWay and OneTime.

Example ViewModel​

[ViewModel]
public partial class TodoListViewModel
{
    [OneTimeBind]
    private IReadOnlyObservableListSync<TodoItemViewModel> _items;

    public TodoListViewModel(TodoStorage storage)
    {
        _items = storage.Todos.CreateSync(
            todo => new TodoItemViewModel(todo)
        );
    }
}

MonoBinder variant: ObservableListViewModelMonoBinder.

ViewModelCollectionBinder<T>​

For static collections with pre-created Views:

// Inspector: the _views array is filled in advance
// On bind: View[0].Initialize(collection[0]), View[1].Initialize(collection[1])...
// Extra Views are hidden through SetActive(false)

Fits a fixed number of items (for example 5 inventory slots).

VirtualizedListItemSourceBinder​

Sets the ItemsSource of a VirtualizedList:

[ViewModel]
public partial class ListViewModel
{
    [OneTimeBind]
    private FilteredList<ItemViewModel> _filteredItems;

    [OneTimeBind]
    private ObservableList<ItemViewModel> _items;

    public ListViewModel()
    {
        _items = new ObservableList<ItemViewModel>();
        _filteredItems = new FilteredList<ItemViewModel>(_items);
    }
}

Inspector properties​

PropertyDescription
FilterICollectionFilter<IViewModel>
OrderICollectionOrder<IViewModel>

Creates an internal FilteredList<IViewModel> when a filter or an order is set.

Mode: OneTime.

View Factories​

Factories are used by ViewModelObservableListBinder to create Views:

PrefabViewFactory​

Creates Views through Object.Instantiate:

Create(viewModel) → Instantiate(prefab) → SetSibling → Initialize(viewModel)
Release(view) → DestroyViewAndGameObject()

PrefabViewPool​

Reuses Views through an ObjectPool:

Create(viewModel) → Pool.Get() → Initialize(viewModel) → SetActive(true)
Release(view) → Deinitialize() → SetActive(false) → Pool.Release()

Properties:

  • _initialCount: initial pool size
  • _maxCount: maximum size
tip

Use PrefabViewPool for lists that update often (chat, feed).

More: View Factories.

Filtering and ordering​

ICollectionFilter<T>​

public interface ICollectionFilter<in T>
{
    bool Matches(T item);
}

Implement it for a custom filter:

[Serializable]
public class CompletedFilter : ICollectionFilter<IViewModel>
{
    public bool Matches(IViewModel item) =>
        item is ItemViewModel viewModel && viewModel.IsCompleted;
}

ICollectionOrder<T>​

public interface ICollectionOrder<in T> : IComparer<T> { }

Implement Compare as for a regular IComparer<T>. An empty slot in the Inspector keeps the source collection order.

Built-in filters​

FilterBehaviour
AndCollectionFilter<T>Passes an item that every nested filter passes
OrCollectionFilter<T>Passes an item that at least one nested filter passes
NotCollectionFilter<T>Inverts the nested filter
ConditionalCollectionFilter<T>Applies the nested filter only while IsEnabled is on
ConverterCollectionFilter<T>Passes an item for which IConverter<T, bool> returned true
PredicateCollectionFilter<T>A wrapper over Predicate<T> for filters from code

An empty nested slot passes everything.

Built-in orders​

OrderBehaviour
SequenceCollectionOrder<T>Applies the nested orders in turn: the first one that tells the items apart decides
InverseCollectionOrder<T>Reverses the nested order
ComparisonCollectionOrder<T>A wrapper over IComparer<T> or Comparison<T> for orders from code

See also​