为什么识别 IsMouseOver 而不能识别 MouseDown(Wpf 样式触发器)? [英] Why IsMouseOver is recognized and MouseDown isn't (Wpf Style trigger)?

问题描述

为什么 IsMouseOver 被识别为 WPF 样式触发器而 MouseDown 不是 - 鉴于两者都是有效的 UIElement 属性，如 见这里-.第一个触发器运行良好，但第二个触发器甚至无法编译.

Why IsMouseOver is recognized as a WPF style trigger and MouseDown isn't -given that both are valid UIElement properties as seen here-. First trigger works well but second one doesn't even compile.

<Style.Triggers>
    <Trigger Property="IsMouseOver" Value="true">
        <Setter Property="OpacityMask">
            <Setter.Value>
                <LinearGradientBrush >
                    <GradientStop Color="Transparent" Offset="0"/>
                    <GradientStop Color="Black" Offset="0.5"/>
                    <GradientStop Color="Transparent" Offset="1"/>
                </LinearGradientBrush>
            </Setter.Value>
        </Setter>
    </Trigger>
    <Trigger Property="MouseDown" Value="true">
        <Setter Property="OpacityMask">
            <Setter.Value>
                <LinearGradientBrush>
                    <GradientStop Color="Black" Offset="0" />
                    <GradientStop Color="White" Offset="1" />
                </LinearGradientBrush>
            </Setter.Value>
        </Setter>
    </Trigger>
</Style.Triggers>

推荐答案

好吧，我猜你把 MouseDown 事件误认为是属性.没有 IsMouseDown 属性，但存在类似的 IsPressed 属性，但仅适用于继承 ButtonBase 的类.如果您想保持代码隐藏干净，您应该只在代码隐藏中使用事件或编写附加属性.

Well, I guess you are mistaking MouseDown event for property. There is no IsMouseDown property but there exist similar IsPressed property but only for classes inheriting ButtonBase. You should just use event in code-behind or write an attached property if you want to keep your code-behind clean.

这就是你的做法.创建类:

This is how you do it. Create class:

using System;
using System.Windows;

namespace Mrpyo
{
    public static class MouseDownHelper 
    {
        public static readonly DependencyProperty IsEnabledProperty = DependencyProperty.RegisterAttached("IsEnabled", 
        typeof(bool), typeof(MouseDownHelper), new FrameworkPropertyMetadata(false, new PropertyChangedCallback(OnNotifyPropertyChanged)));

        public static void SetIsEnabled(UIElement element, bool value)
        {
            element.SetValue(IsEnabledProperty, value);
        }

        public static bool GetIsEnabled(UIElement element)
        {
            return (bool)element.GetValue(IsEnabledProperty);
        }

        private static void OnNotifyPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var element = d as UIElement;
            if (element != null && e.NewValue != null)
            {
                if ((bool)e.NewValue)
                {
                    Register(element);
                }
                else
                {
                    UnRegister(element);
                }
            } 
        }

        private static void Register(UIElement element)
        {
            element.PreviewMouseDown += element_MouseDown;
            element.PreviewMouseLeftButtonDown += element_MouseLeftButtonDown;
            element.MouseLeave += element_MouseLeave;
            element.PreviewMouseUp += element_MouseUp;
        }

        private static void UnRegister(UIElement element)
        {
            element.PreviewMouseDown -= element_MouseDown;
            element.PreviewMouseLeftButtonDown -= element_MouseLeftButtonDown;
            element.MouseLeave -= element_MouseLeave;
            element.PreviewMouseUp -= element_MouseUp;
        }

        private static void element_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            var element = sender as UIElement;
            if (element != null)
            {
                SetIsMouseDown(element, true);
            }
        }

        private static void element_MouseLeftButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            var element = sender as UIElement;
            if (element != null)
            {
                SetIsMouseLeftButtonDown(element, true);
            }
        }

        private static void element_MouseLeave(object sender, System.Windows.Input.MouseEventArgs e)
        {
            var element = sender as UIElement;
            if (element != null)
            {
                SetIsMouseDown(element, false);
                SetIsMouseLeftButtonDown(element, false);
            }
        }

        private static void element_MouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            var element = sender as UIElement;
            if (element != null)
            {
                SetIsMouseDown(element, false);
                SetIsMouseLeftButtonDown(element, false);
            }
        }

        internal static readonly DependencyPropertyKey IsMouseDownPropertyKey = DependencyProperty.RegisterAttachedReadOnly("IsMouseDown",
        typeof(bool), typeof(MouseDownHelper), new FrameworkPropertyMetadata(false));
        public static readonly DependencyProperty IsMouseDownProperty = IsMouseDownPropertyKey.DependencyProperty;

        internal static void SetIsMouseDown(UIElement element, bool value)
        {
            element.SetValue(IsMouseDownPropertyKey, value);
        }

        public static bool GetIsMouseDown(UIElement element)
        {
            return (bool)element.GetValue(IsMouseDownProperty);
        }

        internal static readonly DependencyPropertyKey IsMouseLeftButtonDownPropertyKey = DependencyProperty.RegisterAttachedReadOnly("IsMouseLeftButtonDown",
        typeof(bool), typeof(MouseDownHelper), new FrameworkPropertyMetadata(false));
        public static readonly DependencyProperty IsMouseLeftButtonDownProperty = IsMouseLeftButtonDownPropertyKey.DependencyProperty;

        internal static void SetIsMouseLeftButtonDown(UIElement element, bool value)
        {
            element.SetValue(IsMouseLeftButtonDownPropertyKey, value);
        }

        public static bool GetIsMouseLeftButtonDown(UIElement element)
        {
            return (bool)element.GetValue(IsMouseLeftButtonDownProperty);
        }
    }
}

然后按照你的风格:

<Setter Property="local:MouseDownHelper.IsEnabled" Value="True"/>
<Style.Triggers>
    <Trigger Property="local:MouseDownHelper.IsMouseLeftButtonDown" Value="True">
        <!-- ... -->
    </Trigger>
</Style.Triggers>

当然还要在您的 XAML 文件中添加命名空间(查看顶部):

And of course add namespace in your XAML file (look at the top):

xmlns:local="clr-namespace:Mrpyo"

这篇关于为什么识别 IsMouseOver 而不能识别 MouseDown(Wpf 样式触发器)?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！