maui-collectionview（毛伊岛收藏视图）

CollectionView —.NET MAUI

CollectionView is the primary control for displaying scrollable lists and grids of data in.NET MAUI. It replaces ListView with better performance, flexible layouts, and no ViewCell requirement.

When to Use

• Displaying a scrollable list or grid of data items
• Binding a collection of objects to a templated item layout
• Adding selection (single or multiple), grouping, or pull-to-refresh
• Implementing infinite scroll / incremental loading
• Showing swipe actions on list items
• Displaying an empty state when no data is available

When Not to Use

• Static layouts with a fixed number of items — use Grid or StackLayout directly
• Map pin lists — use the Microsoft.Maui.Controls.Maps NuGet package
• Table-based data entry forms — use standard form controls
• Simple text-only lists with no interaction — consider BindableLayout on a StackLayout

Inputs

• A data source (typically ObservableCollection<T>) bound to ItemsSource
• A DataTemplate defining how each item renders
• Optional: layout configuration, selection mode, grouping model, empty view

Basic Setup

<CollectionView ItemsSource="{Binding Items}">
    <CollectionView.ItemTemplate>
        <DataTemplate x:DataType="models:Item">
            <HorizontalStackLayout Padding="8" Spacing="8">
                <Image Source="{Binding Icon}" WidthRequest="40" HeightRequest="40" />
                <Label Text="{Binding Name}" VerticalOptions="Center" />
            </HorizontalStackLayout>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

Key rules:

• Bind ItemsSource to an ObservableCollection<T> so the UI updates on add/remove.
• Each item template root must be a Layout or View — never use ViewCell.
• Always set x:DataType on DataTemplate for compiled bindings.

Layouts

Set ItemsLayout to control arrangement. Default is VerticalList.

Grid Layout

<CollectionView ItemsSource="{Binding Items}">
    <CollectionView.ItemsLayout>
        <GridItemsLayout Orientation="Vertical"
                         Span="2"
                         VerticalItemSpacing="8"
                         HorizontalItemSpacing="8" />
    </CollectionView.ItemsLayout>
    <CollectionView.ItemTemplate>
        <DataTemplate x:DataType="models:Item">
            <Border Padding="8" StrokeThickness="0">
                <VerticalStackLayout>
                    <Image Source="{Binding Image}" HeightRequest="120" Aspect="AspectFill" />
                    <Label Text="{Binding Name}" FontAttributes="Bold" />
                </VerticalStackLayout>
            </Border>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

Horizontal List

<CollectionView ItemsSource="{Binding Items}"
                ItemsLayout="HorizontalList" />

Selection

Selection Mode

<CollectionView ItemsSource="{Binding Items}"
                SelectionMode="Single"
                SelectedItem="{Binding CurrentItem, Mode=TwoWay}"
                SelectionChangedCommand="{Binding ItemSelectedCommand}" />

For Multiple selection, bind SelectedItems (type IList<object>):

<CollectionView SelectionMode="Multiple"
                SelectedItems="{Binding ChosenItems, Mode=OneWay}" />

Selected Visual State

Highlight selected items using VisualStateManager:

<CollectionView.ItemTemplate>
    <DataTemplate x:DataType="models:Item">
        <Grid Padding="8">
            <VisualStateManager.VisualStateGroups>
                <VisualStateGroup Name="CommonStates">
                    <VisualState Name="Normal">
                        <VisualState.Setters>
                            <Setter Property="BackgroundColor" Value="Transparent" />
                        </VisualState.Setters>
                    </VisualState>
                    <VisualState Name="Selected">
                        <VisualState.Setters>
                            <Setter Property="BackgroundColor"
                                    Value="{AppThemeBinding Light={StaticResource Primary}, Dark={StaticResource PrimaryDark}}" />
                        </VisualState.Setters>
                    </VisualState>
                </VisualStateGroup>
            </VisualStateManager.VisualStateGroups>
            <Label Text="{Binding Name}" />
        </Grid>
    </DataTemplate>
</CollectionView.ItemTemplate>

Grouping

1. Create a group class inheriting from List<T>:

public class AnimalGroup : List<Animal>
{
    public string Name { get; }
    public AnimalGroup(string name, List<Animal> animals) : base(animals)
    {
        Name = name;
    }
}

1. Bind to ObservableCollection<AnimalGroup> and set IsGrouped="True":

<CollectionView ItemsSource="{Binding AnimalGroups}"
                IsGrouped="True">
    <CollectionView.GroupHeaderTemplate>
        <DataTemplate x:DataType="models:AnimalGroup">
            <Label Text="{Binding Name}"
                   FontAttributes="Bold"
                   BackgroundColor="{StaticResource Gray100}"
                   Padding="8" />
        </DataTemplate>
    </CollectionView.GroupHeaderTemplate>
    <CollectionView.ItemTemplate>
        <DataTemplate x:DataType="models:Animal">
            <Label Text="{Binding Name}" Padding="16,4" />
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

Pull-to-Refresh

Wrap CollectionView in a RefreshView. Set IsRefreshing back to false when done:

<RefreshView IsRefreshing="{Binding IsRefreshing}"
             Command="{Binding RefreshCommand}">
    <CollectionView ItemsSource="{Binding Items}" />
</RefreshView>

Incremental Loading (Infinite Scroll)

<CollectionView ItemsSource="{Binding Items}"
                RemainingItemsThreshold="5"
                RemainingItemsThresholdReachedCommand="{Binding LoadMoreCommand}" />

⚠️ Do NOT use with non-virtualizing layouts. LinearItemsLayout and GridItemsLayout support virtualization. Using BindableLayout on a StackLayout as an alternative to CollectionView has no virtualization, which triggers infinite threshold-reached events.

SwipeView — Binding from Inside DataTemplate

Commands inside a DataTemplate can't directly reach your ViewModel. Use RelativeSource AncestorType:

<CollectionView.ItemTemplate>
    <DataTemplate x:DataType="models:Item">
        <SwipeView>
            <SwipeView.RightItems>
                <SwipeItems>
                    <SwipeItem Text="Delete"
                               BackgroundColor="Red"
                               Command="{Binding BindingContext.DeleteCommand, Source={RelativeSource AncestorType={x:Type ContentPage}}}"
                               CommandParameter="{Binding}" />
                </SwipeItems>
            </SwipeView.RightItems>
            <Grid Padding="8">
                <Label Text="{Binding Name}" />
            </Grid>
        </SwipeView>
    </DataTemplate>
</CollectionView.ItemTemplate>

EmptyView

Shown when ItemsSource is empty or null.

<CollectionView ItemsSource="{Binding SearchResults}"
                EmptyView="No items found." />

For a custom empty view, wrap in ContentView:

<CollectionView ItemsSource="{Binding SearchResults}">
    <CollectionView.EmptyView>
        <ContentView>
            <VerticalStackLayout HorizontalOptions="Center" VerticalOptions="Center">
                <Image Source="empty_state.png" WidthRequest="120" />
                <Label Text="Nothing here yet" HorizontalTextAlignment="Center" />
            </VerticalStackLayout>
        </ContentView>
    </CollectionView.EmptyView>
</CollectionView>

Headers and Footers

<CollectionView ItemsSource="{Binding Items}">
    <CollectionView.Header>
        <Label Text="Header" FontAttributes="Bold" Padding="8" />
    </CollectionView.Header>
    <CollectionView.Footer>
        <Label Text="Footer" FontAttributes="Italic" Padding="8" />
    </CollectionView.Footer>
</CollectionView>

Use HeaderTemplate / FooterTemplate when headers or footers are data-bound.

Scrolling

ScrollTo

Programmatically scroll by index or item:

// Scroll to index
collectionView.ScrollTo(index: 10, position: ScrollToPosition.Center, animate: true);

// Scroll to item
collectionView.ScrollTo(item: myItem, position: ScrollToPosition.MakeVisible, animate: true);

Snap Points

<CollectionView.ItemsLayout>
    <LinearItemsLayout Orientation="Horizontal"
                       SnapPointsType="MandatorySingle"
                       SnapPointsAlignment="Center" />
</CollectionView.ItemsLayout>

• SnapPointsType: None, Mandatory, MandatorySingle
• SnapPointsAlignment: Start, Center, End

Performance Tips

• Use MeasureFirstItem for uniform item sizes — significantly faster than MeasureAllItems: <LinearItemsLayout Orientation="Vertical" ItemSizingStrategy="MeasureFirstItem" />
• Always use ObservableCollection<T>, not List<T>. Swapping a List forces a full re-render.
• Update collections on the UI thread — MainThread.BeginInvokeOnMainThread(() => Items.Add(item)).

Common Pitfalls

References

• CollectionView overview
• CollectionView layout
• CollectionView selection
• CollectionView grouping
• CollectionView scrolling
• CollectionView EmptyView