如何为具有 MVVM 架构的 WinRT 应用重用 XAML 中的交互行为

Question

为了绑定 "loaded" 和 "unloaded" 事件，我在 XAML 页面中使用了以下代码：

<Page ...>
<interactivity:Interaction.Behaviors>
    <core:EventTriggerBehavior EventName="Loaded">
        <core:InvokeCommandAction Command="{Binding LoadedCommand}" />
    </core:EventTriggerBehavior>
    <core:EventTriggerBehavior EventName="Unloaded">
        <core:InvokeCommandAction Command="{Binding UnloadedCommand}" />
    </core:EventTriggerBehavior>
</interactivity:Interaction.Behaviors>
<Grid />
</Page>

一切都按预期工作，但是我正在将这段相同的代码复制到每个视图中吗？我怎样才能使它可重用？

编辑

我使用此中的代码创建了一个附件属性。

我的附件属性看起来像这样：

public static class UiBehaviors
{
    public static readonly DependencyProperty AttachedTriggersProperty = DependencyProperty.RegisterAttached("AttachedTriggers", typeof(EventTriggerCollection), typeof(UiBehaviors), new PropertyMetadata(null, OnAttachedTriggersChanged));

    private static void OnAttachedTriggersChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        BehaviorCollection triggers = Interaction.GetBehaviors(d);

        if (e.OldValue != null)
        {
            foreach (EventTriggerBehavior trigger in (EventTriggerCollection)e.OldValue)
                triggers.Remove(trigger);
        }

        if (e.NewValue == null)
            return;

        foreach (EventTriggerBehavior trigger in (EventTriggerCollection)e.NewValue)
            triggers.Add(trigger);

    }

    public static void SetAttachedTriggers(DependencyObject element, EventTriggerCollection value)
    {
        element.SetValue(AttachedTriggersProperty, value);
    }

    public static EventTriggerCollection GetAttachedTriggers(DependencyObject element)
    {
        return (EventTriggerCollection)element.GetValue(AttachedTriggersProperty);
    }
}

public class EventTriggerCollection : Collection<EventTriggerBehavior>
{
}

我的 Xaml 看起来像这样：

<Style x:Name="Test" TargetType="UserControl">
    <Setter Property="storeApplication:UiBehaviors.AttachedTriggers">
        <Setter.Value>
            <storeApplication:EventTriggerCollection>
                <core:EventTriggerBehavior EventName="Loaded">
                    <core:InvokeCommandAction Command="{Binding LoadedCommand}"  />
                </core:EventTriggerBehavior>
                <core:EventTriggerBehavior EventName="Unloaded">
                    <core:InvokeCommandAction Command="{Binding UnloadedCommand}" />
                </core:EventTriggerBehavior>
            </storeApplication:EventTriggerCollection>
        </Setter.Value>
    </Setter>
</Style>

EventTriggerCollection 需要 x:shared=False 属性，以便在每次访问属性时创建一组新的触发器。没有它，触发器将只对访问属性的第一个控件起作用。

不幸的是，我无法使用此属性，因为它在 WinRT 中不受支持。看到这个 post。我现在卡住了:(我错过了什么？

Answer 1

您可以子class您的页面或定义附加的属性在单个属性中执行相同的操作。

例如对于基础 class 解决方案：

MainPage.xaml

<local:MyAppPageBase
    x:Class="App16.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App16"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    LoadedCommand="{Binding LoadedCommand}"
    UnloadedCommand="{Binding UnloadedCommand}">
    <Grid />
</local:MyAppPageBase>

MainPage.xaml.cs

using System.Windows.Input;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace App16
{
    public abstract class MyAppPageBase : Page
    {
        #region LoadedCommand
        /// <summary>
        /// LoadedCommand Dependency Property
        /// </summary>
        private static readonly DependencyProperty _LoadedCommandProperty =
            DependencyProperty.Register(
                "LoadedCommand",
                typeof(ICommand),
                typeof(MyAppPageBase),
                new PropertyMetadata(null));

        /// <summary>
        /// Identifies the LoadedCommand dependency property.
        /// </summary>
        public static DependencyProperty LoadedCommandProperty { get { return _LoadedCommandProperty; } }

        /// <summary>
        /// Gets or sets the LoadedCommand property. This dependency property 
        /// indicates the command to execute when the page loads.
        /// </summary>
        public ICommand LoadedCommand
        {
            get { return (ICommand)GetValue(LoadedCommandProperty); }
            set { this.SetValue(LoadedCommandProperty, value); }
        }
        #endregion

        #region UnloadedCommand
        /// <summary>
        /// UnloadedCommand Dependency Property
        /// </summary>
        private static readonly DependencyProperty _UnloadedCommandProperty =
            DependencyProperty.Register(
                "UnloadedCommand",
                typeof(ICommand),
                typeof(MyAppPageBase),
                new PropertyMetadata(null));

        /// <summary>
        /// Identifies the UnloadedCommand dependency property.
        /// </summary>
        public static DependencyProperty UnloadedCommandProperty { get { return _UnloadedCommandProperty; } }

        /// <summary>
        /// Gets or sets the UnloadedCommand property. This dependency property 
        /// indicates the command to execute when the page unloads.
        /// </summary>
        public ICommand UnloadedCommand
        {
            get { return (ICommand)GetValue(UnloadedCommandProperty); }
            set { this.SetValue(UnloadedCommandProperty, value); }
        }
        #endregion

        public MyAppPageBase()
        {
            this.Loaded += (s, e) =>
            {
                if (LoadedCommand?.CanExecute(null) == true)
                {
                    LoadedCommand.Execute(null);
                }
            };

            this.Unloaded += (s, e) =>
            {
                if (UnloadedCommand?.CanExecute(null) == true)
                {
                    UnloadedCommand.Execute(null);
                }
            };
        }
    }

    public sealed partial class MainPage : MyAppPageBase
    {
        public MainPage()
        {
            this.InitializeComponent();
        }
    }
}

Attached 属性（附加行为）解决方案有点复杂，因为 attached 属性需要确保它不会导致由静态 [=40 上的事件订阅引起的泄漏=]，但好处是不需要更改基础 classes，如果您想在多个项目中重用它，这一点特别有用，也许可以将其放入 NuGet 包中：

MainPage.xaml

<Page
    x:Class="App16.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App16"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    local:ElementExtensions.LoadedCommand="{Binding LoadedCommand}">
    <Grid />
</Page>

MainPage.xaml.cs

using System;
using System.Diagnostics;
using System.Windows.Input;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace App16
{
    public static class ElementExtensions
    {
        #region LoadedCommand
        /// <summary>
        /// LoadedCommand Attached Dependency Property
        /// </summary>
        private static readonly DependencyProperty _LoadedCommandProperty =
            DependencyProperty.RegisterAttached(
                "LoadedCommand",
                typeof(ICommand),
                typeof(ElementExtensions),
                new PropertyMetadata(null, OnLoadedCommandChanged));

        /// <summary>
        /// Identifies the LoadedCommand dependency property.
        /// </summary>
        public static DependencyProperty LoadedCommandProperty { get { return _LoadedCommandProperty; } }

        /// <summary>
        /// Gets the LoadedCommand property. This dependency property 
        /// indicates the command to execute when the element loads.
        /// </summary>
        public static ICommand GetLoadedCommand(DependencyObject d)
        {
            return (ICommand)d.GetValue(LoadedCommandProperty);
        }

        /// <summary>
        /// Sets the LoadedCommand property. This dependency property 
        /// indicates the command to execute when the element loads.
        /// </summary>
        public static void SetLoadedCommand(DependencyObject d, ICommand value)
        {
            d.SetValue(LoadedCommandProperty, value);
        }

        /// <summary>
        /// Handles changes to the LoadedCommand property.
        /// </summary>
        /// <param name="d">
        /// The <see cref="DependencyObject"/> on which
        /// the property has changed value.
        /// </param>
        /// <param name="e">
        /// Event data that is issued by any event that
        /// tracks changes to the effective value of this property.
        /// </param>
        private static void OnLoadedCommandChanged(
            DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ICommand oldLoadedCommand = (ICommand)e.OldValue;
            ICommand newLoadedCommand = (ICommand)d.GetValue(LoadedCommandProperty);

            if (oldLoadedCommand != null)
            {
                var handler = GetLoadedCommandHandler(d);
                handler?.Detach((FrameworkElement) d);
            }

            if (newLoadedCommand != null)
            {
                SetLoadedCommandHandler(d, new LoadedCommandHandler((FrameworkElement)d));
            }
        }
        #endregion

        #region LoadedCommandHandler
        /// <summary>
        /// LoadedCommandHandler Attached Dependency Property
        /// </summary>
        private static readonly DependencyProperty _LoadedCommandHandlerProperty =
            DependencyProperty.RegisterAttached(
                "LoadedCommandHandler",
                typeof(LoadedCommandHandler),
                typeof(ElementExtensions),
                new PropertyMetadata(null));

        /// <summary>
        /// Identifies the LoadedCommandHandler dependency property.
        /// </summary>
        public static DependencyProperty LoadedCommandHandlerProperty { get { return _LoadedCommandHandlerProperty; } }

        /// <summary>
        /// Gets the LoadedCommandHandler property. This dependency property 
        /// indicates the object that handles Loaded events on its owning element.
        /// </summary>
        internal static LoadedCommandHandler GetLoadedCommandHandler(DependencyObject d)
        {
            return (LoadedCommandHandler)d.GetValue(LoadedCommandHandlerProperty);
        }

        /// <summary>
        /// Sets the LoadedCommandHandler property. This dependency property 
        /// indicates the object that handles Loaded events on its owning element.
        /// </summary>
        internal static void SetLoadedCommandHandler(DependencyObject d, LoadedCommandHandler value)
        {
            d.SetValue(LoadedCommandHandlerProperty, value);
        }
        #endregion

        internal class LoadedCommandHandler
        {
            public LoadedCommandHandler(FrameworkElement element)
            {
                element.Loaded += OnLoaded;
            }

            public void Detach(FrameworkElement element)
            {
                element.Loaded -= OnLoaded;
            }

            private void OnLoaded(object sender, RoutedEventArgs e)
            {
                var command = GetLoadedCommand((DependencyObject) sender);
                if (command?.CanExecute(null) == true)
                {
                    command.Execute(null);
                }
            }
        }
    }

    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
            this.DataContext = new MyViewModel();
        }
    }

    public class MyViewModel
    {
        public ICommand LoadedCommand { get; private set; } = new MyCommand();
    }

    public class MyCommand : ICommand
    {
        public bool CanExecute(object parameter)
        {
            return true;
        }

        public void Execute(object parameter)
        {
            Debug.WriteLine("Blahr");
        }

        public event EventHandler CanExecuteChanged;
    }
}

如何为具有 MVVM 架构的 WinRT 应用重用 XAML 中的交互行为

How to reuse Interaction Behavior in XAML for WinRT app with an MVVM architecture

xaml

mvvm

windows-runtime

behavior

reusability