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：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：
ViewModelDataContext绑定到ViewModel上(创建一个DesignModel用来给设计器提供数据)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ValueConverterView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
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
<?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
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>
{
}public abstract class BaseValueConverter<T> : MarkupExtension, IValueConverterwhere 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;elsereturn (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}" /><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
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。
<TextBoxText="{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);elseawait 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);}
}<TextBlockRenderTransformOrigin="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：
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);
}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);
}<ScrollViewerx: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：
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 eventscrollViewer.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);}}
}<ScrollViewerlocal:MouseWheelEventBubbleUpAttachedProperty.Value="True"VerticalScrollBarVisibility="Auto"><ItemsControl ItemsSource="{Binding Items}"><ItemsControl.ItemTemplate><DataTemplate><!-- 可能包含子ScrollView --></DataTemplate></ItemsControl.ItemTemplate></ItemsControl>
</ScrollViewer>转载于:.html
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