c# - 在 WPF 中，您可以在没有代码隐藏的情况下过滤 CollectionViewSource 吗？

Question

真的，这个主题说明了一切。

<CollectionViewSource x:Key="MyData"
    Source="{Binding}" Filter="{ SomethingMagicInXaml? }" />

并不是说我不能有代码在后面。它只会对我唠叨。

Answer 1

如果您“足够努力”，您几乎可以在 XAML 中做任何事情，up to writing whole programs in it .

你永远不会绕过代码背后(好吧，如果你使用库，你不必编写任何但应用程序当然仍然依赖它)，这是一个在这种特定情况下你可以做什么的例子:

<CollectionViewSource x:Key="Filtered" Source="{Binding DpData}"
                      xmlns:me="clr-namespace:Test.MarkupExtensions">
    <CollectionViewSource.Filter>
        <me:Filter>
            <me:PropertyFilter PropertyName="Name" Value="Skeet" />
        </me:Filter>
    </CollectionViewSource.Filter>
</CollectionViewSource>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Markup;
using System.Windows.Data;
using System.Collections.ObjectModel;
using System.Windows;
using System.Text.RegularExpressions;

namespace Test.MarkupExtensions
{
    [ContentProperty("Filters")]
    class FilterExtension : MarkupExtension
    {
        private readonly Collection<IFilter> _filters = new Collection<IFilter>();
        public ICollection<IFilter> Filters { get { return _filters; } }

        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            return new FilterEventHandler((s, e) =>
                {
                    foreach (var filter in Filters)
                    {
                        var res = filter.Filter(e.Item);
                        if (!res)
                        {
                            e.Accepted = false;
                            return;
                        }
                    }
                    e.Accepted = true;
                });
        }
    }

    public interface IFilter
    {
        bool Filter(object item);
    }

    // Sketchy Example Filter
    public class PropertyFilter : DependencyObject, IFilter
    {
        public static readonly DependencyProperty PropertyNameProperty =
            DependencyProperty.Register("PropertyName", typeof(string), typeof(PropertyFilter), new UIPropertyMetadata(null));
        public string PropertyName
        {
            get { return (string)GetValue(PropertyNameProperty); }
            set { SetValue(PropertyNameProperty, value); }
        }
        public static readonly DependencyProperty ValueProperty =
            DependencyProperty.Register("Value", typeof(object), typeof(PropertyFilter), new UIPropertyMetadata(null));
        public object Value
        {
            get { return (object)GetValue(ValueProperty); }
            set { SetValue(ValueProperty, value); }
        }
        public static readonly DependencyProperty RegexPatternProperty =
            DependencyProperty.Register("RegexPattern", typeof(string), typeof(PropertyFilter), new UIPropertyMetadata(null));
        public string RegexPattern
        {
            get { return (string)GetValue(RegexPatternProperty); }
            set { SetValue(RegexPatternProperty, value); }
        }

        public bool Filter(object item)
        {
            var type = item.GetType();
            var itemValue = type.GetProperty(PropertyName).GetValue(item, null);
            if (RegexPattern == null)
            {
                return (object.Equals(itemValue, Value));
            }
            else
            {
                if (itemValue is string == false)
                {
                    throw new Exception("Cannot match non-string with regex.");
                }
                else
                {
                    return Regex.Match((string)itemValue, RegexPattern).Success;
                }
            }
        }
    }
}

如果您想在 XAML 中做一些事情，标记扩展是您的 friend 。

(您可能想拼出扩展的名称，即 me:FilterExtension，因为 Visual Studio 中的即时检查可能会无缘无故地提示，它仍然可以编译和当然可以运行，但警告可能很烦人。
也不希望 CollectionViewSource.Filter 出现在 IntelliSense 中，它不希望您通过 XML-element-notation 设置该处理程序)