是否可以在 EventTrigger 中给出条件？我为单选按钮编写了以下 EventTrigger (Mouse.MouseLeave)。我希望不应该为处于选中状态（IsChecked = True）的项目触发此操作。
<EventTrigger RoutedEvent="Mouse.MouseLeave" SourceName="border">
<BeginStoryboard Name="out_BeginStoryboard" Storyboard="{StaticResource out}" />
<RemoveStoryboard BeginStoryboardName="over_BeginStoryboard" />
</EventTrigger>
请告诉我如何实现这一目标？
提前致谢。
【问题讨论】：
标签： wpf
您不能以这种方式使用 EventTrigger。调用 EventTriggers 的 WPF 的 RoutedEventHandler 没有提供任何使触发器有条件的机制，并且您无法通过子类化 TriggerAction 来解决此问题，因为没有要覆盖的受保护的 Invoke() 或 Execute() 操作。
然而，这可以很容易地使用自定义类来完成。以下是它的使用方法：
<Border>
<my:ConditionalEventTrigger.Triggers>
<my:ConditionalEventTriggerCollection>
<my:ConditionalEventTrigger RoutedEvent="Mouse.MouseLeave"
Condition="{Binding IsChecked, ElementName=checkbox}">
<BeginStoryboard Name="out_BeginStoryboard" Storyboard="{StaticResource out}" />
<RemoveStoryboard BeginStoryboardName="over_BeginStoryboard" />
</my:ConditionalEventTrigger>
</my:ConditionalEventTriggerCollection>
</my:ConditionalEventTrigger.Triggers>
...
以下是它的实现方式：
[ContentProperty("Actions")]
public class ConditionalEventTrigger : FrameworkContentElement
{
public RoutedEvent RoutedEvent { get; set; }
public List<TriggerAction> Actions { get; set; }
// Condition
public bool Condition { get { return (bool)GetValue(ConditionProperty); } set { SetValue(ConditionProperty, value); } }
public static readonly DependencyProperty ConditionProperty = DependencyProperty.Register("Condition", typeof(bool), typeof(ConditionalEventTrigger));
// "Triggers" attached property
public static ConditionalEventTriggerCollection GetTriggers(DependencyObject obj) { return (ConditionalEventTriggerCollection)obj.GetValue(TriggersProperty); }
public static void SetTriggers(DependencyObject obj, ConditionalEventTriggerCollection value) { obj.SetValue(TriggersProperty, value); }
public static readonly DependencyProperty TriggersProperty = DependencyProperty.RegisterAttached("Triggers", typeof(ConditionalEventTriggerCollection), typeof(ConditionalEventTrigger), new PropertyMetadata
{
PropertyChangedCallback = (obj, e) =>
{
// When "Triggers" is set, register handlers for each trigger in the list
var element = (FrameworkElement)obj;
var triggers = (List<ConditionalEventTrigger>)e.NewValue;
foreach(var trigger in triggers)
element.AddHandler(trigger.RoutedEvent, new RoutedEventHandler((obj2, e2) =>
trigger.OnRoutedEvent(element)));
}
});
public ConditionalEventTrigger()
{
Actions = new List<TriggerAction>();
}
// When an event fires, check the condition and if it is true fire the actions
void OnRoutedEvent(FrameworkElement element)
{
DataContext = element.DataContext; // Allow data binding to access element properties
if(Condition)
{
// Construct an EventTrigger containing the actions, then trigger it
var dummyTrigger = new EventTrigger { RoutedEvent = _triggerActionsEvent };
foreach(var action in Actions)
dummyTrigger.Actions.Add(action);
element.Triggers.Add(dummyTrigger);
try
{
element.RaiseEvent(new RoutedEventArgs(_triggerActionsEvent));
}
finally
{
element.Triggers.Remove(dummyTrigger);
}
}
}
static RoutedEvent _triggerActionsEvent = EventManager.RegisterRoutedEvent("", RoutingStrategy.Direct, typeof(EventHandler), typeof(ConditionalEventTrigger));
}
// Create collection type visible to XAML - since it is attached we cannot construct it in code
public class ConditionalEventTriggerCollection : List<ConditionalEventTrigger> {}
享受吧！
【讨论】：
sealed internal 并拍打他们 :-( 无论如何，当你尝试（并失败）用一堆方法来实现条件事件触发器时，你几乎结束了与您在此处获得的确切解决方案一致。我添加的一个小调整是，它仅在条件更改时添加和删除虚拟触发器，而不是每次触发事件时。
这对我有用...
我想根据鼠标悬停在 UI 元素上并且 UI 元素的关联所有者处于活动状态（即启用以使玩家移动）来执行动画。
为了支持这些要求，我使用了相对源绑定来克服对事件触发条件的支持不足。
例子：
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding RelativeSource={RelativeSource self}, Path=IsMouseOver}" Value="True" />
<Condition Binding="{Binding Path=IsPlayer1Active}" Value="True" />
</MultiDataTrigger.Conditions>
<MultiDataTrigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<ColorAnimation Storyboard.TargetProperty="Background.GradientStops[0].Color" To="#FF585454" Duration="0:0:.25"/>
<ColorAnimation Storyboard.TargetProperty="Background.GradientStops[1].Color" To="Black" Duration="0:0:2"/>
</Storyboard>
</BeginStoryboard>
</MultiDataTrigger.EnterActions>
</MultiDataTrigger>
【讨论】：
这是我修改后的Ray's answer 版本，它仅在设置源触发器时创建和附加虚拟事件，而不是每次都这样做。我认为这对我的场景会更好，因为我要针对数百个项目发起事件，而不仅仅是一两个：
[ContentProperty("Actions")]
public class ConditionalEventTrigger : FrameworkContentElement
{
static readonly RoutedEvent DummyEvent = EventManager.RegisterRoutedEvent(
"", RoutingStrategy.Direct, typeof(EventHandler), typeof(ConditionalEventTrigger));
public static readonly DependencyProperty TriggersProperty = DependencyProperty.RegisterAttached(
"Triggers", typeof(ConditionalEventTriggers), typeof(ConditionalEventTrigger),
new FrameworkPropertyMetadata(RefreshTriggers));
public static readonly DependencyProperty ConditionProperty = DependencyProperty.Register(
"Condition", typeof(bool), typeof(ConditionalEventTrigger)); // the Condition is evaluated whenever an event fires
public ConditionalEventTrigger()
{
Actions = new List<TriggerAction>();
}
public static ConditionalEventTriggers GetTriggers(DependencyObject obj)
{ return (ConditionalEventTriggers)obj.GetValue(TriggersProperty); }
public static void SetTriggers(DependencyObject obj, ConditionalEventTriggers value)
{ obj.SetValue(TriggersProperty, value); }
public bool Condition
{
get { return (bool)GetValue(ConditionProperty); }
set { SetValue(ConditionProperty, value); }
}
public RoutedEvent RoutedEvent { get; set; }
public List<TriggerAction> Actions { get; set; }
// --- impl ----
// we can't actually fire triggers because WPF won't let us (stupid sealed internal methods)
// so, for each trigger, make a dummy trigger (on a dummy event) with the same actions as the real trigger,
// then attach handlers for the dummy event
public static void RefreshTriggers(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
var targetObj = (FrameworkElement)obj;
// start by clearing away the old triggers
foreach (var t in targetObj.Triggers.OfType<DummyEventTrigger>().ToArray())
targetObj.Triggers.Remove(t);
// create and add dummy triggers
foreach (var t in ConditionalEventTrigger.GetTriggers(targetObj))
{
t.DataContext = targetObj.DataContext; // set and Track DataContext so binding works
// targetObj.GetDataContextChanged().WeakSubscribe(dc => t.DataContext = targetObj.DataContext);
var dummyTrigger = new DummyEventTrigger { RoutedEvent = DummyEvent };
foreach (var action in t.Actions)
dummyTrigger.Actions.Add(action);
targetObj.Triggers.Add(dummyTrigger);
targetObj.AddHandler(t.RoutedEvent, new RoutedEventHandler((o, args) => {
if (t.Condition) // evaluate condition when the event gets fired
targetObj.RaiseEvent(new RoutedEventArgs(DummyEvent));
}));
}
}
class DummyEventTrigger : EventTrigger { }
}
public class ConditionalEventTriggers : List<ConditionalEventTrigger> { }
它是这样使用的：
<Border>
<local:ConditionalEventTrigger.Triggers>
<local:ConditionalEventTriggers>
<local:ConditionalEventTrigger RoutedEvent="local:ClientEvents.Flash" Condition="{Binding IsFlashing}">
<BeginStoryboard Name="FlashAnimation">...
线
// targetObj.GetDataContextChanged().WeakSubscribe(dc => t.DataContext = targetObj.DataContext);
正在使用我写的响应式框架和一些扩展方法，基本上我们需要订阅目标对象的.DataContextChanged事件，但是我们需要使用弱引用来完成。如果您的对象从未更改其数据上下文，那么您根本不需要此代码
【讨论】：
我知道这是一篇旧帖子，但是当我最终在这里寻求答案时，这对我有用。基本上我想要一个面板，它会在鼠标悬停时从屏幕右侧进行动画处理，然后在鼠标离开时返回。但是，只有当面板没有固定时。 IsShoppingCartPinned 属性存在于我的 ViewModel 上。就您的场景而言，您可以将 IsShoppingCartPinned 属性替换为您的复选框 IsChecked 属性，并在 EventTriggers 上运行任何类型的动画。
代码如下：
<Grid.Style>
<Style TargetType="{x:Type Grid}">
<Setter Property="Margin" Value="0,20,-400,20"/>
<Setter Property="Grid.Column" Value="0"/>
<Style.Triggers>
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding IsShoppingCartPinned}" Value="False"/>
<Condition Binding="{Binding RelativeSource={RelativeSource Self}, Path=IsMouseOver}" Value="True"/>
</MultiDataTrigger.Conditions>
<MultiDataTrigger.EnterActions>
<BeginStoryboard Name="ExpandPanel">
<Storyboard>
<ThicknessAnimation Duration="0:0:0.1" Storyboard.TargetProperty="Margin" To="0,20,0,20"/>
</Storyboard>
</BeginStoryboard>
</MultiDataTrigger.EnterActions>
<MultiDataTrigger.ExitActions>
<BeginStoryboard Name="HidePanel">
<Storyboard>
<ThicknessAnimation Duration="0:0:0.1" Storyboard.TargetProperty="Margin" To="0,20,-400,20"/>
</Storyboard>
</BeginStoryboard>
</MultiDataTrigger.ExitActions>
</MultiDataTrigger>
<DataTrigger Binding="{Binding IsShoppingCartPinned}" Value="True">
<DataTrigger.EnterActions>
<RemoveStoryboard BeginStoryboardName="ExpandPanel"/>
<RemoveStoryboard BeginStoryboardName="HidePanel"/>
</DataTrigger.EnterActions>
<DataTrigger.Setters>
<Setter Property="Margin" Value="0"/>
<Setter Property="Grid.Column" Value="1"/>
</DataTrigger.Setters>
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Style>
【讨论】：
根据您的情况，您需要：
<EventTrigger RoutedEvent="Checked" SourceName="border">
编辑： 根据您的 cmets，您正在寻找一个多数据触发器。
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition SourceName="border" Property="IsMouseOver" Value="false" />
</MultiDataTrigger.Conditions>
<MultiDataTrigger.EnterActions>
<BeginStoryboard Name="out_BeginStoryboard" Storyboard="{StaticResource out}" />
<RemoveStoryboard BeginStoryboardName="over_BeginStoryboard" />
</MultiDataTrigger.EnterActions>
</MultiDataTrigger>
【讨论】：
<Condition SourceName="checkbox" Proerty="IsChecked" Value="True" />）
基于 Ray 和 Orion，这是我的版本，目标是您可以将 2 个触发器绑定到一个按钮，并在单击时翻转状态（或更多状态，如果您愿意，它应该适用于所有 Control）。当您绑定 ConditionProperty 时，您必须将 ConditionValue 写为 False 表示 True，将 Ture 表示为 False，这有点棘手。我猜这是因为在更新绑定之前执行了按钮的事件处理程序。它是这样使用的：
<Button x:Name="HoldButton" Content="{Binding Status.Running}"/>
<mut:ConditionalEventTrigger.ConditionTriggers>
<mut:ConditionalEventTriggers>
<mut:ConditionalEventTrigger RoutedEvent="ButtonBase.Click" ConditionProperty="{Binding Status.Running}" ConditionValue="False">
<BeginStoryboard x:Name="OnHold_BeginStoryboard" Storyboard="{StaticResource OnHold}"/>
</mut:ConditionalEventTrigger>
<mut:ConditionalEventTrigger RoutedEvent="ButtonBase.Click" ConditionProperty="{Binding Status.Running}" ConditionValue="True">
<StopStoryboard BeginStoryboardName="OnHold_BeginStoryboard"/>
</mut:ConditionalEventTrigger>
</mut:ConditionalEventTriggers>
</mut:ConditionalEventTrigger.ConditionTriggers>
</Button>
代码如下：
using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Markup;
namespace MyUtility.Trigger
{
[ContentProperty("Actions")]
public class ConditionalEventTrigger : FrameworkContentElement
{
public static readonly DependencyProperty ConditionTriggersProperty = DependencyProperty.RegisterAttached(
"ConditionTriggers",
typeof(ConditionalEventTriggers),
typeof(ConditionalEventTrigger),
new FrameworkPropertyMetadata(OnConditionalEventTriggersChanged));
public static ConditionalEventTriggers GetConditionTriggers(FrameworkElement element)
{
return (ConditionalEventTriggers)element.GetValue(ConditionTriggersProperty);
}
public static void SetConditionTriggers(FrameworkElement element, List<ConditionalEventTrigger> value)
{
element.SetValue(ConditionTriggersProperty, value);
}
public static readonly DependencyProperty ConditionPropertyProperty = DependencyProperty.Register(
"ConditionProperty",
typeof(bool),
typeof(ConditionalEventTrigger));
public bool ConditionProperty
{
get
{
return (bool)GetValue(ConditionPropertyProperty);
}
set
{
SetValue(ConditionPropertyProperty, value);
}
}
public static readonly DependencyProperty ConditionValueProperty = DependencyProperty.Register(
"ConditionValue",
typeof(bool),
typeof(ConditionalEventTrigger));
public bool ConditionValue
{
get
{
return (bool)GetValue(ConditionValueProperty);
}
set
{
SetValue(ConditionValueProperty, value);
}
}
private static readonly RoutedEvent m_DummyEvent = EventManager.RegisterRoutedEvent(
"ConditionalEventTriggerDummyEvent",
RoutingStrategy.Direct,
typeof(EventHandler),
typeof(ConditionalEventTrigger));
public RoutedEvent RoutedEvent { get; set; }
public List<TriggerAction> Actions { get; set; }
public ConditionalEventTrigger()
{
Actions = new List<TriggerAction>();
}
public static void OnConditionalEventTriggersChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
var element = (FrameworkElement)obj;
var triggers = (ConditionalEventTriggers)e.NewValue;
foreach(ConditionalEventTrigger t in triggers)
{
element.RemoveHandler(t.RoutedEvent, new RoutedEventHandler((obj2, e2) => t.OnRoutedEvent(element)));
element.AddHandler(t.RoutedEvent, new RoutedEventHandler((obj2, e2) => t.OnRoutedEvent(element)));
}
}
public void OnRoutedEvent(FrameworkElement element)
{
this.DataContext = element.DataContext;
if (this.ConditionProperty == this.ConditionValue)
{
// .Net doesn't allow us fire a trigger directly, so we bingd trigger on Element and then fire the element.
var dummyTrigger = new EventTrigger { RoutedEvent = m_DummyEvent };
foreach (TriggerAction action in this.Actions)
{
dummyTrigger.Actions.Add(action);
}
element.Triggers.Add(dummyTrigger);
try
{
element.RaiseEvent(new RoutedEventArgs(m_DummyEvent));
}
finally
{
element.Triggers.Remove(dummyTrigger);
}
}
}
}
public class ConditionalEventTriggers : List<ConditionalEventTrigger> {}
}
【讨论】：