c# - 绑定(bind)到 ListView 上 ObservableCollection 中的前 N ​​项

Question

我有一个 ObservableCollection<T>在我的应用程序中可以容纳许多项目。具体来说，这是来自潜在广泛记录器的摘要信息。我想做的是将此集合的前 3 项严格绑定(bind)到 WPF ListView .

是否有 XAML 语法或足够简单的方法来在我的 VM 中创建次要属性，以始终返回集合中的前 3 项并像正常一样更新对集合的任何更改 ObservableCollection<T>如果您正在与完整列表进行交互，您会这样做吗？

Answer 1

您可以推出自己的 ObservableCollection<T>具有返回顶部项目的属性。

举个例子

代码:

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Linq;
using System.Windows;

namespace WpfApplication1
{
    public partial class MainWindow
    {
        public MyCollection Collection { get; }

        public MainWindow()
        {
            InitializeComponent();

            Collection = new MyCollection();

            DataContext = Collection;
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            Collection.Add(Collection.Count);
        }
    }

    public sealed class MyCollection : ObservableCollection<int>
    {
        public MyCollection()
        {
            CollectionChanged += MyCollection_CollectionChanged;
        }

        private void MyCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {   // to notify XAML-side binding
            OnPropertyChanged(new PropertyChangedEventArgs(nameof(TopItems)));
        }

        public IEnumerable<int> TopItems => this.Take(3);
    }
}

XAML:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:local="clr-namespace:WpfApplication1"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        Title="MainWindow"
        Width="525"
        Height="350"
        d:DataContext="{d:DesignInstance local:MyCollection}"
        mc:Ignorable="d">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Button Click="button_Click" Content="Button" />
        <ListBox Grid.Row="1" ItemsSource="{Binding}" />
        <ListBox Grid.Row="2" ItemsSource="{Binding TopItems}" />
    </Grid>
</Window>