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Handle ItemsSource updates without an ObservableCollection (#138)
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132 changes: 132 additions & 0 deletions
132
src/BlazorBindings.Maui/Elements/Internal/ItemsSourceComponent.cs
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,132 @@ | ||
| using System.Collections.ObjectModel; | ||
| using System.Diagnostics; | ||
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| namespace BlazorBindings.Maui.Elements.Internal; | ||
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| /// <summary> | ||
| /// This component creates an observable collection, which is updated by blazor renderer. | ||
| /// This allows to use it for cases, when MAUI expects an ObservableCollection to handle the updates, | ||
| /// but instead of forcing the user to use ObservableCollection on their side, we manage the updates by Blazor. | ||
| /// Probably not the most performant way, is there any other option? | ||
| /// </summary> | ||
| internal class ItemsSourceComponent<TControl, TItem> : NativeControlComponentBase, IElementHandler, IContainerElementHandler, INonPhysicalChild | ||
| { | ||
| private readonly ObservableCollection<TItem> _observableCollection = new(); | ||
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| [Parameter] | ||
| public IEnumerable<TItem> Items { get; set; } | ||
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| [Parameter] | ||
| public Action<TControl, ObservableCollection<TItem>> CollectionSetter { get; set; } | ||
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| [Parameter] | ||
| public Func<TItem, object> KeySelector { get; set; } | ||
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| private TControl _parent; | ||
| public object TargetElement => _parent; | ||
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| private HashSet<object> _keys; | ||
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| protected override RenderFragment GetChildContent() => builder => | ||
| { | ||
| _keys?.Clear(); | ||
| bool shouldAddKey = true; | ||
| int index = 0; | ||
| foreach (var item in Items) | ||
| { | ||
| var key = KeySelector == null ? item : KeySelector(item); | ||
| if (KeySelector == null) | ||
| { | ||
| // Blazor doesn't allow duplicate keys. Therefore we add keys until the first duplicate. | ||
| // In case KeySelector is provided, we don't check for that here, since it's user's responsibility now. | ||
| _keys ??= new(); | ||
| shouldAddKey &= _keys.Add(key); | ||
| if (!shouldAddKey) | ||
| key = null; | ||
| } | ||
| builder.OpenComponent<ItemHolderComponent>(1); | ||
| builder.SetKey(key); | ||
| builder.AddAttribute(2, nameof(ItemHolderComponent.Item), item); | ||
| builder.AddAttribute(3, nameof(ItemHolderComponent.Index), index); | ||
| builder.AddAttribute(4, nameof(ItemHolderComponent.ObservableCollection), _observableCollection); | ||
| if (key != null) | ||
| builder.AddAttribute(5, nameof(ItemHolderComponent.HasKey), true); | ||
| builder.CloseComponent(); | ||
| index++; | ||
| } | ||
| }; | ||
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| void IContainerElementHandler.AddChild(object child, int physicalSiblingIndex) | ||
| { | ||
| _observableCollection.Insert(physicalSiblingIndex, (TItem)child); | ||
| } | ||
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| void IContainerElementHandler.RemoveChild(object child, int physicalSiblingIndex) | ||
| { | ||
| Debug.Assert(Equals(_observableCollection[physicalSiblingIndex], child)); | ||
| _observableCollection.RemoveAt(physicalSiblingIndex); | ||
| } | ||
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| void IContainerElementHandler.ReplaceChild(int physicalSiblingIndex, object oldChild, object newChild) | ||
| { | ||
| Debug.Assert(Equals(_observableCollection[physicalSiblingIndex], oldChild)); | ||
| if (!Equals(_observableCollection[physicalSiblingIndex], newChild)) | ||
| _observableCollection[physicalSiblingIndex] = (TItem)newChild; | ||
| } | ||
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| public void RemoveFromParent(object parentElement) | ||
| { | ||
| } | ||
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| public void SetParent(object parentElement) | ||
| { | ||
| _parent = (TControl)parentElement; | ||
| CollectionSetter(_parent, _observableCollection); | ||
| } | ||
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| private class ItemHolderComponent : NativeControlComponentBase, IElementHandler | ||
| { | ||
| [Parameter] | ||
| public TItem Item { get; set; } | ||
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| [Parameter] | ||
| public ObservableCollection<TItem> ObservableCollection { get; set; } | ||
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| [Parameter] | ||
| public int? Index { get; set; } | ||
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| [Parameter] | ||
| public bool HasKey { get; set; } | ||
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| public object TargetElement => Item; | ||
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| public override Task SetParametersAsync(ParameterView parameters) | ||
| { | ||
| var previousIndex = Index; | ||
| var previousItem = Item; | ||
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| // Task should be completed immediately | ||
| var task = base.SetParametersAsync(parameters); | ||
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| if (previousIndex == null) | ||
| return task; | ||
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| if (previousIndex == Index && Equals(previousItem, Item)) | ||
| return task; | ||
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| // Generally it will not be invoked, but it is needed when Source has duplicate items, or component has key. | ||
| // The problem here is that we don't know whether previous items are going to be removed or added. | ||
| // We use previousIndex here, because this part of the code is executed before items are actually added/removed to ObservableCollection. | ||
| if ((HasKey || previousIndex == Index) && !Equals(ObservableCollection[previousIndex.Value], Item)) | ||
| ObservableCollection[previousIndex.Value] = Item; | ||
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| return task; | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,53 @@ | ||
| using Microsoft.AspNetCore.Components.Rendering; | ||
| using System.Collections.Immutable; | ||
| using System.Collections.Specialized; | ||
| using MC = Microsoft.Maui.Controls; | ||
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| namespace BlazorBindings.Maui.Elements; | ||
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| public abstract partial class ItemsView<T> | ||
| { | ||
| [Parameter] public IEnumerable<T> ItemsSource { get; set; } | ||
| [Parameter] public Func<T, object> ItemKeySelector { get; set; } | ||
| [Parameter] public RenderFragment<T> ItemTemplateSelector { get; set; } | ||
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| // Whether we should attempt to create ObservableCollection on our own (via diffing), or assign it directly. | ||
| private bool AssignItemsSourceDirectly => ItemsSource is INotifyCollectionChanged || ItemsSource is IImmutableList<T>; | ||
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| protected override bool HandleAdditionalParameter(string name, object value) | ||
| { | ||
| switch (name) | ||
| { | ||
| case nameof(ItemsSource): | ||
| if (!Equals(ItemsSource, value)) | ||
| { | ||
| ItemsSource = (IEnumerable<T>)value; | ||
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| if (AssignItemsSourceDirectly) | ||
| NativeControl.ItemsSource = ItemsSource; | ||
| } | ||
| return true; | ||
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| case nameof(ItemKeySelector): | ||
| ItemKeySelector = (Func<T, object>)value; | ||
| return true; | ||
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| case nameof(ItemTemplateSelector): | ||
| ItemTemplateSelector = (RenderFragment<T>)value; | ||
| return true; | ||
| } | ||
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| return base.HandleAdditionalParameter(name, value); | ||
| } | ||
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| protected override void RenderAdditionalPartialElementContent(RenderTreeBuilder builder, ref int sequence) | ||
| { | ||
| base.RenderAdditionalPartialElementContent(builder, ref sequence); | ||
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| RenderTreeBuilderHelper.AddDataTemplateSelectorProperty<MC.ItemsView, T>(builder, sequence++, ItemTemplateSelector, (x, template) => x.ItemTemplate = template); | ||
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| sequence++; | ||
| if (!AssignItemsSourceDirectly) | ||
| RenderTreeBuilderHelper.AddItemsSourceProperty<MC.ItemsView, T>(builder, sequence, ItemsSource, ItemKeySelector, (x, items) => x.ItemsSource = items); | ||
| } | ||
| } |
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60 changes: 60 additions & 0 deletions
60
src/BlazorBindings.UnitTests/Elements/CollectionViewTests.razor
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,60 @@ | ||
| @using System.Collections.Specialized; | ||
| @using System.Collections.ObjectModel; | ||
| @using System.Collections.Immutable; | ||
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| @inherits ElementTestBase | ||
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| @code { | ||
| [Test] | ||
| public async Task CreateCollectionViewWithItemTemplate() | ||
| { | ||
| var items = new (int Index, string Name)[] { (1, "First"), (2, "Seconds"), (3, ("Third")) }; | ||
| var collectionView = await Render<MC.CollectionView>( | ||
| @<CollectionView ItemsSource="items"> | ||
| <ItemTemplate> | ||
| <VerticalStackLayout> | ||
| <Label>@context.Index</Label> | ||
| <Label>@context.Name</Label> | ||
| </VerticalStackLayout> | ||
| </ItemTemplate> | ||
| </CollectionView>); | ||
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| // It's nice that it doesn't crash at least, but is there any way to get templated items here?... | ||
| Assert.That(collectionView.ItemsSource, Is.EqualTo(items)); | ||
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| // For a regular collections we attempt to detect changes in the collection. | ||
| Assert.That(collectionView.ItemsSource is INotifyCollectionChanged); | ||
| } | ||
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| [Test] | ||
| public async Task ObservableItemsViewIsAssignedDirectly() | ||
| { | ||
| var items = new ObservableCollection<int>(new[] { 1, 2, 3, 4 }); | ||
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| var collectionView = await Render<MC.CollectionView>( | ||
| @<CollectionView ItemsSource="items"> | ||
| <ItemTemplate> | ||
| <Label>@context</Label> | ||
| </ItemTemplate> | ||
| </CollectionView>); | ||
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| // Since collection is already observable, no need to diff additionally. | ||
| Assert.That(collectionView.ItemsSource, Is.SameAs(items)); | ||
| } | ||
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| [Test] | ||
| public async Task ImmutableItemsViewIsAssignedDirectly() | ||
| { | ||
| var items = ImmutableList.Create(1, 2, 3, 4); | ||
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| var collectionView = await Render<MC.CollectionView>( | ||
| @<CollectionView ItemsSource="items"> | ||
| <ItemTemplate> | ||
| <Label>@context</Label> | ||
| </ItemTemplate> | ||
| </CollectionView>); | ||
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| // Since collection is immutable, there is no point in detecting changes there. | ||
| Assert.That(collectionView.ItemsSource, Is.SameAs(items)); | ||
| } | ||
| } |
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