MVVM "Thumb.DragStarted"事件的问题

Question

我试图通过使用MVVMLight EventToCommand触发Slider Thumb.DragStarted事件，但它不起作用。同样的事情是完美的滑块事件ValueChanged。

下面是我的代码:

<Slider
    Width="150"
    AutoToolTipPlacement="BottomRight"
    AutoToolTipPrecision="2"
    IsSnapToTickEnabled="True"
    Maximum="{Binding SilderMaxValue}"
    Minimum="0"
    Value="{Binding SliderValue}">                                        
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="ValueChanged">
                <cmd:EventToCommand
                    Command="{Binding SliderValueChangedCommand}"
                    PassEventArgsToCommand="True" />
             </i:EventTrigger>
        <i:EventTrigger EventName="Thumb.DragStarted">
                <cmd:EventToCommand
                    Command="{Binding SliderDragStartedCommand}"
                    PassEventArgsToCommand="True" />
        </i:EventTrigger>                                  
</Slider>

谢谢. .

Answer 1

我看到了你的帖子，而我正试图做类似的事情(尽管与Thumb.DragCompleted)。在任何情况下，我都使用了附加属性。我将把我的解决方案贴出来，以防对任何人有用。

---

SliderDragBehavoirs.cs:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;
using System.Windows.Media;
namespace WpfApplication1
{
    public static class SliderDragBehaviors
    {
        public static readonly DependencyProperty DragCompletedCommandProperty =
            DependencyProperty.RegisterAttached("DragCompletedCommand", typeof(ICommand), typeof(SliderDragBehaviors),
            new FrameworkPropertyMetadata(new PropertyChangedCallback(DragCompleted)));
        private static void DragCompleted(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var slider = (Slider)d;
            var thumb = GetThumbFromSlider(slider);
            thumb.DragCompleted += thumb_DragCompleted;
        }
        private static void thumb_DragCompleted(object sender, DragCompletedEventArgs e)
        {
            FrameworkElement element = (FrameworkElement)sender;
            element.Dispatcher.Invoke(() =>
                {
                    var command = GetDragCompletedCommand(element);
                    var slider = FindParentControl<Slider>(element) as Slider;
                    command.Execute(slider.Value);
                });
        }
        public static void SetDragCompletedCommand(UIElement element, ICommand value)
        {
            element.SetValue(DragCompletedCommandProperty, value);
        }
        public static ICommand GetDragCompletedCommand(FrameworkElement element)
        {
            var slider = FindParentControl<Slider>(element);
            return (ICommand)slider.GetValue(DragCompletedCommandProperty);
        }
        private static Thumb GetThumbFromSlider(Slider slider)
        {
            var track = slider.Template.FindName("PART_Track", slider) as Track;
            return track == null ? null : track.Thumb;
        }
        private static DependencyObject FindParentControl<T>(DependencyObject control)
        {
            var parent = VisualTreeHelper.GetParent(control);
            while (parent != null && !(parent is T))
            {
                parent = VisualTreeHelper.GetParent(parent);
            }
            return parent;
        }
    }
}

这里有几件事值得注意。因为该命令是连接到Slider的，但是事件是在Thumb上触发的，所以必须能够向上/向下查看可视化树，以便从另一个树中获取一个。

---

XAML例子:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:behaviors="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525">
    <Grid x:Name="grid">
        <Slider behaviors:SliderDragBehaviors.DragCompletedCommand="{Binding Path=DragCompletedCommand}"/>
    </Grid>
</Window>

---

希望对你有帮助

Answer 2

我对Tom Allen的代码有一个问题，因为滑块模板在我想用命令绑定它的时候不可用。基本上，我所需要做的就是等待滑块控件加载并再次尝试。下面是我需要做的修改，以使它工作:

    private static void DragCompleted(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        //the Template of the slider is not available now
        //we have to wait for the slider to load completely in order to do this
        var slider = (Slider)d;
        slider.Loaded += slider_Loaded;
    }
    static void slider_Loaded(object sender, RoutedEventArgs e)
    {
        var slider = (Slider)sender;
        var thumb = GetThumbFromSlider(slider);
        thumb.DragCompleted += thumb_DragCompleted;
    }

希望有帮助!关于