使用EventTrigger设置属性

Question

我想使用EventTrigger来设置某个属性，但是存在一些问题：

1) EventTriggers只支持Actions，所以我必须使用storyBoard来设置属性。

2) 当我使用storyboard时，有两个选项：

• Stop：动画停止后，值会恢复到动画开始之前的状态
• HoldEnd：这会锁定属性，使得无论是代码还是用户交互都无法更改动画所持有的属性

在下面的示例中，当按钮被点击时，我想将IsChecked属性设置为False，并且我想让用户能够更改IsChecked，或者我想通过代码更改该属性。

示例:

<EventTrigger
    SourceName="myButton"
    RoutedEvent="Button.Click">
    <EventTrigger.Actions>
        <BeginStoryboard>
            <Storyboard>
                <BooleanAnimationUsingKeyFrames
                    Storyboard.TargetName="myCheckBox"
                    Storyboard.TargetProperty="IsChecked"
                    FillBehavior="Stop">
                    <DiscreteBooleanKeyFrame
                        KeyTime="00:00:00"
                        Value="False" />
                </BooleanAnimationUsingKeyFrames>
            </Storyboard>
        </BeginStoryboard>
    </EventTrigger.Actions>
</EventTrigger>

我意识到可以在故事板完成后使用“Completed”事件将值设置为False。 但是，在这种情况下，我希望将逻辑包含在XAML中，因为此逻辑将用于自定义控件，并且仅限于UI。

- Chris Nicol

Answer 1

只需创建您自己的操作。

namespace WpfUtil
{
    using System.Reflection;
    using System.Windows;
    using System.Windows.Interactivity;


    /// <summary>
    /// Sets the designated property to the supplied value. TargetObject
    /// optionally designates the object on which to set the property. If
    /// TargetObject is not supplied then the property is set on the object
    /// to which the trigger is attached.
    /// </summary>
    public class SetPropertyAction : TriggerAction<FrameworkElement>
    {
        // PropertyName DependencyProperty.

        /// <summary>
        /// The property to be executed in response to the trigger.
        /// </summary>
        public string PropertyName
        {
            get { return (string)GetValue(PropertyNameProperty); }
            set { SetValue(PropertyNameProperty, value); }
        }

        public static readonly DependencyProperty PropertyNameProperty
            = DependencyProperty.Register("PropertyName", typeof(string),
            typeof(SetPropertyAction));


        // PropertyValue DependencyProperty.

        /// <summary>
        /// The value to set the property to.
        /// </summary>
        public object PropertyValue
        {
            get { return GetValue(PropertyValueProperty); }
            set { SetValue(PropertyValueProperty, value); }
        }

        public static readonly DependencyProperty PropertyValueProperty
            = DependencyProperty.Register("PropertyValue", typeof(object),
            typeof(SetPropertyAction));


        // TargetObject DependencyProperty.

        /// <summary>
        /// Specifies the object upon which to set the property.
        /// </summary>
        public object TargetObject
        {
            get { return GetValue(TargetObjectProperty); }
            set { SetValue(TargetObjectProperty, value); }
        }

        public static readonly DependencyProperty TargetObjectProperty
            = DependencyProperty.Register("TargetObject", typeof(object),
            typeof(SetPropertyAction));


        // Private Implementation.

        protected override void Invoke(object parameter)
        {
            object target = TargetObject ?? AssociatedObject;
            PropertyInfo propertyInfo = target.GetType().GetProperty(
                PropertyName,
                BindingFlags.Instance|BindingFlags.Public
                |BindingFlags.NonPublic|BindingFlags.InvokeMethod);

            propertyInfo.SetValue(target, PropertyValue);
        }
    }
}

在这种情况下，我将绑定到我的视图模型上名为DialogResult的属性。

<Grid>

    <Button>
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Click">
                <wpf:SetPropertyAction PropertyName="DialogResult" TargetObject="{Binding}"
                                       PropertyValue="{x:Static mvvm:DialogResult.Cancel}"/>
            </i:EventTrigger>
        </i:Interaction.Triggers>
        Cancel
    </Button>

</Grid>

- Neutrino

Answer 2

虽然我非常喜欢XAML，但对于这种任务，我会切换到代码后台。 附加行为是一种很好的模式。请注意，Expression Blend 3 提供了一种标准方法来编写和使用行为。在Expression社区网站上有一些现有的行为。

- Sergey Aldoukhov

Answer 3

我修改了Neutrino的解决方案，使得在指定值时xaml看起来不那么冗长：

抱歉没有呈现xaml的图片，想象一下一个[=]汉堡按钮，你单击它后它会变成[<-]返回按钮，并切换Grid的可见性。

xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"

...

<Grid>
    <Button x:Name="optionsButton">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Click">
                <local:SetterAction PropertyName="Visibility" Value="Collapsed" />
                <local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsBackButton}" Value="Visible" />
                <local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsPanel}" Value="Visible" />
            </i:EventTrigger>
        </i:Interaction.Triggers>

        <glyphs:Hamburger Width="10" Height="10" />
    </Button>

    <Button x:Name="optionsBackButton" Visibility="Collapsed">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Click">
                <local:SetterAction PropertyName="Visibility" Value="Collapsed" />
                <local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsButton}" Value="Visible" />
                <local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsPanel}" Value="Collapsed" />
            </i:EventTrigger>
        </i:Interaction.Triggers>

        <glyphs:Back Width="12" Height="11" />
    </Button>
</Grid>

...

<Grid Grid.RowSpan="2" x:Name="optionsPanel" Visibility="Collapsed">

</Grid>

您也可以像Neutrino的解决方案一样，使用这种方式指定值：

<Button x:Name="optionsButton">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="Click">
            <local:SetterAction PropertyName="Visibility" Value="{x:Static Visibility.Collapsed}" />
            <local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsBackButton}" Value="{x:Static Visibility.Visible}" />
            <local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsPanel}" Value="{x:Static Visibility.Visible}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>

    <glyphs:Hamburger Width="10" Height="10" />
</Button>

这里是代码。

using System;
using System.ComponentModel;
using System.Reflection;
using System.Windows;
using System.Windows.Interactivity;

namespace Mvvm.Actions
{
    /// <summary>
    /// Sets a specified property to a value when invoked.
    /// </summary>
    public class SetterAction : TargetedTriggerAction<FrameworkElement>
    {
        #region Properties

        #region PropertyName

        /// <summary>
        /// Property that is being set by this setter.
        /// </summary>
        public string PropertyName
        {
            get { return (string)GetValue(PropertyNameProperty); }
            set { SetValue(PropertyNameProperty, value); }
        }

        public static readonly DependencyProperty PropertyNameProperty =
            DependencyProperty.Register("PropertyName", typeof(string), typeof(SetterAction),
            new PropertyMetadata(String.Empty));

        #endregion

        #region Value

        /// <summary>
        /// Property value that is being set by this setter.
        /// </summary>
        public object Value
        {
            get { return (object)GetValue(ValueProperty); }
            set { SetValue(ValueProperty, value); }
        }

        public static readonly DependencyProperty ValueProperty =
            DependencyProperty.Register("Value", typeof(object), typeof(SetterAction),
            new PropertyMetadata(null));

        #endregion

        #endregion

        #region Overrides

        protected override void Invoke(object parameter)
        {
            var target = TargetObject ?? AssociatedObject;

            var targetType = target.GetType();

            var property = targetType.GetProperty(PropertyName, BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static | BindingFlags.Instance);
            if (property == null)
                throw new ArgumentException(String.Format("Property not found: {0}", PropertyName));

            if (property.CanWrite == false)
                throw new ArgumentException(String.Format("Property is not settable: {0}", PropertyName));

            object convertedValue;

            if (Value == null)
                convertedValue = null;

            else
            {
                var valueType = Value.GetType();
                var propertyType = property.PropertyType;

                if (valueType == propertyType)
                    convertedValue = Value;

                else
                {
                    var propertyConverter = TypeDescriptor.GetConverter(propertyType);

                    if (propertyConverter.CanConvertFrom(valueType))
                        convertedValue = propertyConverter.ConvertFrom(Value);

                    else if (valueType.IsSubclassOf(propertyType))
                        convertedValue = Value;

                    else
                        throw new ArgumentException(String.Format("Cannot convert type '{0}' to '{1}'.", valueType, propertyType));
                }
            }

            property.SetValue(target, convertedValue);
        }

        #endregion
    }
}

编辑：Interactivity DLL不再是Blend的一部分，现在是“Microsoft.Xaml.Behaviors.Wpf”NuGet包。代码在此处列出：https://github.com/microsoft/XamlBehaviorsWpf

参见：https://devblogs.microsoft.com/dotnet/open-sourcing-xaml-behaviors-for-wpf/

从旧版Blend Microsoft.Expression.Interactions.dll迁移到新的开源Interactivity dll的步骤（希望我的旧注释是正确的；p）：

1. Install the "Microsoft.Xaml.Behaviors.Wpf" NuGet package.

2. Edit xaml files:
       Replace 'http://schemas.microsoft.com/expression/2010/interactivity' and
               'http://schemas.microsoft.com/expression/2010/interactions'

               with 'http://schemas.microsoft.com/xaml/behaviors'.

       Replace 'xmlns:ei="clr-namespace:Microsoft.Expression.Interactivity.Core;assembly=Microsoft.Expression.Interactions"' and
               'xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"'

               with 'xmlns:i="http://schemas.microsoft.com/xaml/behaviors"'.

3. Edit C# files:
       Replace usings in c# files 'Microsoft.Xaml.Interactivity' and
                                  'Microsoft.Xaml.Interactions'

                                  with 'Microsoft.Xaml.Behaviors'.

       Remove references to 'Microsoft.Expression.Interactions' and
                            'System.Windows.Interactivity'.

- FocusedWolf

---

当使用<local:SetterAction PropertyName="Visibility" TargetObject="{Binding ElementName=optionsPanel}" Value="{x:Static Visibility.Visible}" />时，TargetObject始终为null。 - huoxudong125

@Neutrino 我有一个关于 TargetedTriggerAction 的问题 https://stackoverflow.com/questions/40478172/why-the-targetedtriggeractions-targetobject-is-always-null - huoxudong125

Answer 4

停止Storyboard可以在代码后台或xaml中完成，具体取决于需求的来源。

如果将EventTrigger移出按钮，则可以使用另一个EventTrigger来定位它，并告诉Storyboard停止。以这种方式停止Storyboard时，它不会恢复到先前的值。

在这里，我将Button.Click EventTrigger移动到周围的StackPanel中，并在CheckBox.Click上添加了一个新的EventTrigger，以便在单击CheckBox时停止Button的Storyboard。这样，我们可以在单击时检查和取消选中CheckBox，并从按钮中获得所需的取消选中行为。

    <StackPanel x:Name="myStackPanel">

        <CheckBox x:Name="myCheckBox"
                  Content="My CheckBox" />

        <Button Content="Click to Uncheck"
                x:Name="myUncheckButton" />

        <Button Content="Click to check the box in code."
                Click="OnClick" />

        <StackPanel.Triggers>

            <EventTrigger RoutedEvent="Button.Click"
                          SourceName="myUncheckButton">
                <EventTrigger.Actions>
                    <BeginStoryboard x:Name="myBeginStoryboard">
                        <Storyboard x:Name="myStoryboard">
                            <BooleanAnimationUsingKeyFrames Storyboard.TargetName="myCheckBox"
                                                            Storyboard.TargetProperty="IsChecked">
                                <DiscreteBooleanKeyFrame KeyTime="00:00:00"
                                                         Value="False" />
                            </BooleanAnimationUsingKeyFrames>
                        </Storyboard>
                    </BeginStoryboard>
                </EventTrigger.Actions>
            </EventTrigger>

            <EventTrigger RoutedEvent="CheckBox.Click"
                          SourceName="myCheckBox">
                <EventTrigger.Actions>
                    <StopStoryboard BeginStoryboardName="myBeginStoryboard" />
                </EventTrigger.Actions>
            </EventTrigger>

        </StackPanel.Triggers>
    </StackPanel>

为了在代码后台停止故事板，我们需要进行一些稍微不同的操作。第三个按钮提供了一种方法，通过代码停止故事板并将IsChecked属性设置回true。

我们不能调用myStoryboard.Stop()，因为我们没有通过代码设置isControllable参数开始故事板。相反，我们可以删除故事板。为此，我们需要存在故事板的FrameworkElement，在这种情况下是我们的StackPanel。一旦故事板被移除，我们就可以再次设置IsChecked属性，并使其保留到UI中。

    private void OnClick(object sender, RoutedEventArgs e)
    {
        myStoryboard.Remove(myStackPanel);
        myCheckBox.IsChecked = true;
    }

- rmoore