wpf 使用 EventTrigger 设置属性

Setting a property with an EventTrigger

提问by Chris Nicol

I want to be able to set a property with an EventTrigger, there's a number of problems with this.

我希望能够使用 EventTrigger 设置属性，这有很多问题。

1) EventTriggers only support Actions, so I must use a storyBoard to set my properties.

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

2) Once I use a storyboard, I have two options:

2）一旦我使用故事板，我有两个选择：

• Stop: Once the animation has stopped the value reverts back to before the animation started
• HoldEnd: This locks the property, so that neither code, nor user interaction can change the property that the animation is holding.

• 停止：一旦动画停止，该值将恢复到动画开始之前
• HoldEnd：这会锁定属性，这样代码和用户交互都不能更改动画所持有的属性。

In the below example, I want to set the IsChecked property to False when the button is clicked and I want the user to be able to change the IsChecked and/or I want to be able to change the property in code.

在下面的示例中，我想在单击按钮时将 IsChecked 属性设置为 False，并且我希望用户能够更改 IsChecked 和/或我希望能够在代码中更改该属性。

Example:

例子：

<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>

I realize that I can use the "Completed" event after the storyboard completes to set the value to False. However, in this instance I want to contain the logic within the XAML, as this logic will be used on a custom control and is only specific to the UI.

我意识到我可以在故事板完成后使用“Completed”事件将该值设置为 False。但是，在本例中，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特定于 UI。

采纳答案by Sergey Aldoukhov

As much as I love XAML, for this kinds of tasks I switch to code behind. Attached behaviorsare a good pattern for this. Keep in mind, Expression Blend 3 provides a standard wayto program and use behaviors. There are a few existing oneson the Expression Community Site.

尽管我喜欢 XAML，但对于此类任务，我切换到代码隐藏。附加行为是一个很好的模式。请记住，Expression Blend 3提供了一种标准的方式来编程和使用行为。有几个现有的表达社区网站。

回答by Neutrino

Just create your own action.

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);
        }
    }
}

In this case I'm binding to a property called DialogResult on my viewmodel.

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>

回答by FocusedWolf

I modified Neutrino's solution to make the xaml look less verbose when specifying the value:

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

Sorry for no pictures of the rendered xaml, just imagine a [=] hamburger button that you click and it turns into [<-] a back button and also toggles the visibility of a Grid.

抱歉，没有渲染的 xaml 的图片，想象一下您单击 [=] 汉堡包按钮，它会变成 [<-] 后退按钮并切换网格的可见性。

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>

You can also specify values this way like in Neutrino's solution:

您还可以像在 Neutrino 的解决方案中那样以这种方式指定值：

<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>

And here's the code.

这是代码。

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
    }
}

回答by rmoore

Stopping the Storyboard can be done in the code behind, or the xaml, depending on where the need comes from.

停止 Storyboard 可以在后面的代码或 xaml 中完成，这取决于需求来自何处。

If the EventTrigger is moved outside of the button, then we can go ahead and target it with another EventTrigger that will tell the storyboard to stop. When the storyboard is stopped in this manner it will not revert to the previous value.

如果 EventTrigger 移到按钮之外，那么我们可以继续使用另一个 EventTrigger 来定位它，该 EventTrigger 会告诉故事板停止。当故事板以这种方式停止时，它不会恢复到以前的值。

Here I've moved the Button.Click EventTrigger to a surrounding StackPanel and added a new EventTrigger on the the CheckBox.Click to stop the Button's storyboard when the CheckBox is clicked. This lets us check and uncheck the CheckBox when it is clicked on and gives us the desired unchecking behavior from the button as well.

在这里，我已将 Button.Click EventTrigger 移至周围的 StackPanel，并在 CheckBox.Click 上添加了一个新的 EventTrigger，以在单击 CheckBox 时停止 Button 的故事板。这使我们可以在单击 CheckBox 时选中和取消选中它，并为我们提供所需的按钮取消选中行为。

    <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>

To stop the storyboard in the code behind, we will have to do something slightly different. The third button provides the method where we will stop the storyboard and set the IsChecked property back to true through code.

为了在后面的代码中停止故事板，我们将不得不做一些稍微不同的事情。第三个按钮提供了我们将停止故事板并通过代码将 IsChecked 属性设置回 true 的方法。

We can't call myStoryboard.Stop() because we did not begin the Storyboard through the code setting the isControllable parameter. Instead, we can remove the Storyboard. To do this we need the FrameworkElement that the storyboard exists on, in this case our StackPanel. Once the storyboard is removed, we can once again set the IsChecked property with it persisting to the UI.

我们不能调用 myStoryboard.Stop() 因为我们没有通过设置 isControllable 参数的代码开始 Storyboard。相反，我们可以删除 Storyboard。为此，我们需要故事板所在的 FrameworkElement，在本例中是我们的 StackPanel。一旦故事板被移除，我们可以再次设置 IsChecked 属性，并将其持久化到 UI。

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