WPF 常见 Hacker Solution 汇总前言及基础篇

前言
MVVM、BaseAttachedProperty、BaseValueConverter、以及动画功能的实现
AttachedProperty实现逆时针顺时针旋转功能
- AP实现动画原理
- 几种动画的坑
ScrollView嵌套导致子ScrollView鼠标滚动事件吞没父ScrollView鼠标滚动事件

前言

最近尝试开发WPF项目中，遇到了很多困难，每次都是StackOverflow流，很多方案都是前所未见的，我觉得有记录的价值，也供以后自己参考，由于时间跨度比较大，有些方案我已经找不到当时查找的资料了。

WPF中给我感触最深的地方是条条道路通罗马，实现一种视觉效果有N种方法，但是有的方法看上去又优雅，The MVVM方式，有的方法看上去就像hack，比较多的是 Attached Property 方式

WPF在今天看来可能是辉煌不再了，有更多的桌面跨平台实现方案，但是我觉得有些编程思想还是很有学习价值的，再加上我自己的项目主要还是在Windows平台上运行为主，今后再考虑用Mono或者.Net Core迁移跨平台，至少目前看下来，WPF仍然是Windows桌面开发的最好选择。

如果你是WPF初学者，又像我一样看书在前几章就被各种 XAML 、 Dependency Property 搞得云里雾里，推荐你去油管上看AngelSix的WPF UI教程，虽然时间长，但是看一遍并参照模仿，能让你迅速从 Winform 的 CodeBehind 模式转为MVVM模式。学习WPF对初学者来说绝对不算简单，所以不要觉得经常去网上找‘XXXX怎么实现’很丢人。

由于我也是初学，如果有不正确的地方欢迎指正，谢谢。

MVVM、BaseAttachedProperty、BaseValueConverter、以及动画功能的实现

MVVM：Model-View-ViewModel，UI层面主要关注的是 View-ViewModel ，WPF可能有一半内容就是在ViewModel变化通知View，View变化通知ViewModel过程中，通常实现某个功能的套路就是：

创建用户自定义控件A、以及对应的ViewModel
将自定义控件的DataContext绑定到ViewModel上(创建一个DesignModel用来给设计器提供数据)
将ViewModel中的属性Bind到自定义控件的子属性上，如果需要转换，创建对应的ValueConverter
对于View上的用户操作例如点击鼠标、按下回车键等，绑定上ViewModel上的Command对象

具体原理我就不多说了，这里主要简单贴上代码实现套路，这里基本照搬AngelSix的方法

BaseViewModel

public class BaseViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged = (sender, e) => { };
    public void OnPropertyChanged(string name)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(name));
    }
}

所有ViewModel全部继承自BaseViewModel，然后安装PropertyChanged.Fody的Nuget包，项目目录增加FodyWeavers.xml文件并写入

<?xml version="1.0" encoding="utf-8" ?>
<Weavers>
  <PropertyChanged/>
</Weavers>

这个包的作用主要是用来在编译的时候将PropertyChanged方法植入到public属性的Set方法中，这样你就不用自己每个Set都写PropertyChanged了，有兴趣研究Fody的同学可以到Github上看看，有很多预编译的强大东东。这是ViewModel项目唯一需要安装的包，其它的例如DI容器，可以随自己喜好安装

BaseAttachedProperty

public abstract class BaseAttachedProperty<Parent, Property>
    where Parent : new()
{
    public event Action<DependencyObject, DependencyPropertyChangedEventArgs> ValueChanged = (sender, e) => { };
    public event Action<DependencyObject, object> ValueUpdated = (sender, value) => { };
    public static Parent Instance { get; private set; } = new Parent();
    public static readonly DependencyProperty ValueProperty = DependencyProperty.RegisterAttached(
        "Value",
        typeof(Property),
        typeof(BaseAttachedProperty<Parent, Property>),
        new UIPropertyMetadata(
            default(Property),
            new PropertyChangedCallback(OnValuePropertyChanged),
            new CoerceValueCallback(OnValuePropertyUpdated)
            ));
    private static void OnValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        (Instance as BaseAttachedProperty<Parent, Property>)?.OnValueChanged(d, e);
        (Instance as BaseAttachedProperty<Parent, Property>)?.ValueChanged(d, e);
    }
    private static object OnValuePropertyUpdated(DependencyObject d, object value)
    {
        (Instance as BaseAttachedProperty<Parent, Property>)?.OnValueUpdated(d, value);
        (Instance as BaseAttachedProperty<Parent, Property>)?.ValueUpdated(d, value);
        return value;
    }
    public static Property GetValue(DependencyObject d) => (Property)d.GetValue(ValueProperty);
    public static void SetValue(DependencyObject d, Property value) => d.SetValue(ValueProperty, value);
    public virtual void OnValueChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e) { }
    public virtual void OnValueUpdated(DependencyObject sender, object value) { }
}

所有Attached Property（例如Grid.Column就是Attached Property，以后都简写作AP）都继承自BaseAttachedProperty，这样如果你想创建一个新的AP就很简单了

public class IsHighlightProperty : BaseAttachedProperty<IsHighlightProperty, bool>
{
}

BaseValueConverter

public abstract class BaseValueConverter<T> : MarkupExtension, IValueConverter
    where T : class, new()
{
    private static readonly T Converter = new T();
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return Converter ;
    }
    public abstract object Convert(object value, Type targetType, object parameter, ureInfo culture);
    public abstract object ConvertBack(object value, Type targetType, object parameter, ureInfo culture);
}

这里增加MarkupExtension的实现，就可以在XAML中直接使用

public class BooleanToVisiblityConverter : BaseValueConverter<BooleanToVisiblityConverter>
{
    public override object Convert(object value, Type targetType, object parameter, ureInfo culture)
    {
        if (parameter == null)
            return (bool)value ? Visibility.Hidden : Visibility.Visible;
        else
            return (bool)value ? Visibility.Visible : Visibility.Hidden;
    }
    public override object ConvertBack(object value, Type targetType, object parameter, ureInfo culture)
    {
        throw new NotImplementedException();
    }
}

<Border Height="4"
        Background="{StaticResource IconHoverBlueBrush}"
        VerticalAlignment="Bottom"
        Visibility="{TemplateBinding local:IsHighlightProperty.Value,Converter={local:BooleanToVisiblityConverter},ConverterParameter=True}" />

动画实现

<Border x:Name="border">
    <!-- Add a render scale transform -->
    <Border.RenderTransform>
        <ScaleTransform />
    </Border.RenderTransform>
    <Border.RenderTransformOrigin>
        <Point X="0.5" Y="0.5" />
    </Border.RenderTransformOrigin>
</Border>
<!-- ... -->
<ControlTemplate.Triggers>
    <EventTrigger RoutedEvent="MouseEnter">
        <BeginStoryboard>
            <Storyboard>
                <DoubleAnimation To="1.4" Duration="0:0:0.15" Storyboard.TargetName="border" Storyboard.TargetProperty="(RenderTransform).(ScaleTransform.ScaleX)" />
                <DoubleAnimation To="1.4" Duration="0:0:0.15" Storyboard.TargetName="border" Storyboard.TargetProperty="(RenderTransform).(ScaleTransform.ScaleY)" />
            </Storyboard>
        </BeginStoryboard>
    </EventTrigger>
</ControlTemplate.Triggers>

主要就是创建Storyboard，然后往里面加各种Animation，还有一种在AP中创建动画的，在下一节介绍

AttachedProperty实现逆时针顺时针旋转功能

AP实现动画原理

这套方法是AngelSix的代码，几经他自己修改，我觉得已经挺完美了，我们先看下调用的时候。

<TextBox
    Text="{Binding EditedText, UpdateSourceTrigger=PropertyChanged}"
    local:AnimateFadeInProperty.Value="{Binding Editing}"
/>

根据ViewModel的值，转为true的时候就会fadeIn，false就会fadeOut，可以和丑陋的XAML说拜拜了，开心。

这是AP的实现

public class AnimateFadeInProperty : AnimateBaseProperty<AnimateFadeInProperty>
{
    protected override async void DoAnimation(FrameworkElement element, bool value, bool firstLoad)
    {
        if (value)
            await element.FadeInAsync(firstLoad, firstLoad ? 0 : 0.3f);
        else
            await element.FadeOutAsync(firstLoad ? 0 : 0.3f);
    }
}

其中继承自AnimateBaseProperty，这个基类封装处理了是否第一次载入、是否已经载入等一系列问题，使用弱引用可以防止内存对象不被回收

public abstract class AnimateBaseProperty<Parent> : BaseAttachedProperty<Parent, bool>
where Parent : BaseAttachedProperty<Parent, bool>, new(){
    private readonly Dictionary<WeakReference, bool> mAlreadyLoaded = new Dictionary<WeakReference, bool>();
    private readonly Dictionary<WeakReference, bool> mFirstLoadValue = new Dictionary<WeakReference, bool>();
    public override void OnValueUpdated(DependencyObject sender, object value)
    {
        if (!(sender is FrameworkElement element))
            return;
        var alreadyLoadedReference = mAlreadyLoaded.FirstOrDefault(f => Equals(f.Key.Target, sender));
        if ((bool) sender.GetValue(ValueProperty) == (bool) value && alreadyLoadedReference.Key != null)
            return;
        if (alreadyLoadedReference.Key == null)
        {
            var weakReference = new WeakReference(sender);
            mAlreadyLoaded[weakReference] = false;
            element.Visibility = Visibility.Hidden;
            async void onLoaded(object ss, RoutedEventArgs ee)
            {
                element.Loaded -= onLoaded;
                await Task.Delay(5);
                var firstLoadReference = mFirstLoadValue.FirstOrDefault(f => Equals(f.Key.Target, sender));
                DoAnimation(element, firstLoadReference.Key != null ? firstLoadReference.Value : (bool) value,
                    true);
                mAlreadyLoaded[weakReference] = true;
            }
            element.Loaded += onLoaded;
        }
        else if (!alreadyLoadedReference.Value)
        {
            mFirstLoadValue[new WeakReference(sender)] = (bool) value;
        }
        else
        {
            DoAnimation(element, (bool) value, false);
        }
    }
    protected virtual void DoAnimation(FrameworkElement element, bool value, bool firstLoad)
    {
    }
}

所有UI Element基本都继承自FrameworkElement，所以这个AP基本可以在任何控件上用，但是要当心Visible和Collapse的问题。

public static class FrameworkElementAnimations
{
    public static async Task FadeInAsync(this FrameworkElement element, bool firstLoad, float seconds = 0.3f)
    {
        var sb = new Storyboard();
        sb.AddFadeIn(seconds);
        sb.Begin(element);
        if (Math.Abs(seconds) > 1e-5 || firstLoad)
            element.Visibility = Visibility.Visible;
        await Task.Delay((int)(seconds * 1000));
    }
}

这是StoryBorder的Helper类，通过这个可以组合多个Animation对象同时执行

public static class StoryboardHelpers
{
    public static void AddFadeIn(this Storyboard storyboard, float seconds, bool from = false)
    {
        var animation = new DoubleAnimation
        {
            Duration = new Duration(TimeSpan.FromSeconds(seconds)),
            To = 1,
        };
        if (from)
            animation.From = 0;
        Storyboard.SetTargetProperty(animation, new PropertyPath("Opacity"));
        storyboard.Children.Add(animation);
    }
}

几种动画的坑

顺时针逆时针旋转

<TextBlock
    RenderTransformOrigin="0.5,0.5"
    local:AnimateCWProperty.Value="{Binding IsExpanded}">
    <TextBlock.RenderTransform>
        <TransformGroup>
            <ScaleTransform />
            <SkewTransform />
            <RotateTransform x:Name="rtAngle" Angle="0" />
            <TranslateTransform />
        </TransformGroup>
    </TextBlock.RenderTransform>
</TextBlock>

这里如果不使用 x:Name 命名 RotateTransform 是无法让动画生效的。

public static void AddRotateCW(this Storyboard storyboard, float seconds)
{
    var animation = new DoubleAnimation
    {
        Duration = new Duration(TimeSpan.FromSeconds(seconds)),
        From = 360,
        To = 180,
    };
    Storyboard.SetTargetName(animation, "rtAngle");
    PropertyPath PropP = new PropertyPath(RotateTransform.AngleProperty);
    Storyboard.SetTargetProperty(animation, PropP);
    storyboard.Children.Add(animation);
}
public static void AddRotateCCW(this Storyboard storyboard, float seconds)
{
    var animation = new DoubleAnimation
    {
        Duration = new Duration(TimeSpan.FromSeconds(seconds)),
        From=180,
        To = 360,
    };
    Storyboard.SetTargetName(animation, "rtAngle");
    PropertyPath PropP = new PropertyPath(RotateTransform.AngleProperty);
    Storyboard.SetTargetProperty(animation, PropP);
    storyboard.Children.Add(animation);
}

参考文献：https://social.msdn.microsoft.com/Forums/vstudio/en-US/86039bcd-c550-43b9-b588-36859cc96479/why-doesnt-this-rotate

变形扩大缩小

同旋转

public static void AddScaleYExpand(this Storyboard storyboard, float seconds)
{
    var animation = new DoubleAnimation
    {
        Duration = new Duration(TimeSpan.FromSeconds(seconds)),
        From = 0,
        To = 1,
    }
    Storyboard.SetTargetName(animation, "stScaleY");
    PropertyPath PropP = new PropertyPath(ScaleTransform.ScaleYProperty);
    Storyboard.SetTargetProperty(animation, PropP)
    storyboard.Children.Add(animation);
}

ScrollView 展开收缩

这个比较麻烦了，用到了 MutiBinding ，主要思想是根据所有子元素的高度，去乘以一个 double 值 Tag ，如果 double 值为0，那么就收起 ScrollView ，如果为1，则全部展开

public static void AddScrollViewExpand(this Storyboard storyboard, float seconds,  FrameworkElement element)
{
    if (DesignerProperties.GetIsInDesignMode(element))
    {
        element.SetValue(FrameworkElement.TagProperty, 1);
        return;
    }
    var animation = new DoubleAnimation
    {
        Duration = new Duration(TimeSpan.FromSeconds(seconds)),
        From = 0,
        To = 1,
    };
    PropertyPath PropP = new PropertyPath("Tag");
    Storyboard.SetTargetProperty(animation, PropP);
    storyboard.Children.Add(animation);
}

<ScrollViewer
        x:Name="ExpandScrollView"
        HorizontalScrollBarVisibility="Hidden"
        VerticalScrollBarVisibility="Hidden"
        HorizontalContentAlignment="Stretch"
        local:AnimateScrollViewExpandProperty.Value="{Binding IsExpand}"
        VerticalContentAlignment="Bottom">
    <ScrollViewer.Tag>
        <system:Double>1.0</system:Double>
    </ScrollViewer.Tag>
    <ScrollViewer.Height>
        <MultiBinding Converter="{local:MultiplyConverter}">
            <Binding Path="ActualHeight" ElementName="ExpanderContent" />
            <Binding Path="Tag" RelativeSource="{RelativeSource Self}" />
        </MultiBinding>
    </ScrollViewer.Height>
    <ContentControl x:Name="ExpanderContent"></ContentControl>
</ScrollViewer>

这里用到了 MultiplyConverter ，可以同时绑定多个数据，照例还是封装一个基类使用

public abstract class BaseMutiValueConverter<T> : MarkupExtension, IMultiValueConverter where T:class,new()
{
    private static readonly T Converter = new T();
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return Converter ;
    }
    public abstract object Convert(object[] values, Type targetType, object parameter, CultureInfo culture);
    public abstract object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture);
}
public class MultiplyConverter : BaseMutiValueConverter<MultiplyConverter>
{
    public override object Convert(object[] values, Type targetType,
        object parameter, CultureInfo culture)
    {
        double result = 1.0;
        foreach (var t in values)
        {
            if (t is double d)
                result *= d;
        }
        return result;
    }
    public override object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

参考文献：https://www.codeproject.com/Articles/248112/Templating-WPF-Expander-Control#animation

ScrollView嵌套导致子ScrollView鼠标滚动事件吞没父ScrollView鼠标滚动事件

如题，在子ScrollView控件中鼠标滚轮的滚动事件会被handle掉，这样，即使你滚动到子控件的底部，父ScrollView仍然不能滚动，这个在做复杂的ScrollView控件时可能会碰到，网上的解决方案使用Code Behind方式，我稍加修改为AP方式，在使用上注意加载顺序

 public class MouseWheelEventBubbleUpAttachedProperty:BaseAttachedProperty<MouseWheelEventBubbleUpAttachedProperty,bool>
{
    public override void OnValueChanged(DependencyObject sender, ndencyPropertyChangedEventArgs e)
    {
        if (!(sender is ScrollViewer scrollViewer)) return;
        if ((bool) e.NewValue)
        {
            void OnLoaded(object s, RoutedEventArgs ee)
            {
                scrollViewer.Loaded -= OnLoaded;
                //Hook the event
                scrollViewer.FindAndActToAllChild<ScrollViewer>((scrollchildview) =>
                {
                    scrollchildview.PreviewMouseWheel += (sss, eee) => PreviewMouseWheel(sss, eee, scrollViewer);
                });
            }
            scrollViewer.Loaded += OnLoaded;
        }
    }
    private void PreviewMouseWheel(object sender, MouseWheelEventArgs e, ScrollViewer scrollViewer)
    {
        if (!e.Handled)
        {
            e.Handled = true;
            var eventArg =
                new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta)
                {
                    RoutedEvent = UIElement.MouseWheelEvent,
                    Source = sender
                };
            scrollViewer.RaiseEvent(eventArg);
        }
    }
}

<ScrollViewer
    local:MouseWheelEventBubbleUpAttachedProperty.Value="True"
    VerticalScrollBarVisibility="Auto">
    <ItemsControl ItemsSource="{Binding Items}">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <!-- 可能包含子ScrollView -->
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</ScrollViewer>

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原文地址：https://www.cnblogs.com/enigmaxp/p/9362988.html

WPF 常见 Hacker Solution 汇总 前言及基础篇

前言