在 WPF 中，您可以在没有代码的情况下过滤 CollectionViewSource 吗? [英] In WPF can you filter a CollectionViewSource without code behind?

问题描述

主题真的说明了一切.

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

并不是我不能有代码.它只是对我唠叨.

It's not that I can't have code behind. It just nags at me.

推荐答案

如果你足够努力"，你几乎可以在 XAML 中做任何事情，最多可以在其中编写整个程序.

You can do pretty much anything in XAML if you "try hard enough", up to writing whole programs in it.

您永远不会绕过代码背后的问题(好吧，如果您使用库，您不必编写任何库，但应用程序当然仍然依赖它)，以下是在这种特定情况下您可以执行的操作的示例:

You will never get around code behind (well, if you use libraries you don't have to write any but the application still relies on it of course), here's an example of what you can do in this specific case:

<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 中做某事，标记扩展是您的朋友.

Markup extensions are your friend if you want to do something in XAML.

(您可能想拼出扩展名，即 me:FilterExtension，因为 Visual Studio 中的即时检查可能会无缘无故地抱怨，它仍然编译并当然可以运行，但警告可能很烦人.
也不要指望 CollectionViewSource.Filter 出现在 IntelliSense 中，它不希望您通过 XML-element-notation 设置该处理程序)

(You might want to spell out the name of the extension, i.e. me:FilterExtension as the on-the-fly checking in Visual Studio may complain without reason, it still compiles and runs of course but the warnings might be annoying.
Also do not expect the CollectionViewSource.Filter to show up in the IntelliSense, it does not expect you to set that handler via XML-element-notation)

这篇关于在 WPF 中，您可以在没有代码的情况下过滤 CollectionViewSource 吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！