Animate Margin Change in Silverlight

问题

I am animating a border resize in Silverlight however I also need to gradually remove the margin around it (currently 50). Blend doesn't seem to generate a tween for margin change - it just jumps from 50 to 0 in one go. Is there a way to achieve this?

回答1:

The problem is that a Margin is really of type "System.Windows.Thickness" which is NOT a dependency object, thus Left, Top, Right, and Bottom are NOT Dependency Properties and thus cannot be animated using DoubleAnimation (which allows for tweening).

What is used to animate the Margin is an ObjectAnimation which does not tween. This is why you see the margin jump from its original location to its new location. As another common example, the same happens when you try to animate the Visibility property between Visible and Collapsed.

You would either need to do timer based animation in order to animate margin or implement your own Animation type for Thickness objects.

回答2:

Ben Lemmon gives an elegant solution: http://blogs.msdn.com/blemmon/archive/2009/03/18/animating-margins-in-silverlight.aspx

回答3:

Here is an updated version that allows you to animate from within XAML

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace NiceCards.Animations
{
    public class ThicknessAnimationX
    {
        public static readonly DependencyProperty ElementProperty = DependencyProperty.RegisterAttached("Element", typeof(DependencyObject), typeof(DoubleAnimation), new PropertyMetadata(new PropertyChangedCallback(OnElementPropertyChanged)));

        // The time along the animation from 0-1
        public static DependencyProperty TimeProperty = DependencyProperty.RegisterAttached("Time", typeof(double), typeof(DoubleAnimation), new PropertyMetadata(OnTimeChanged));

        // The object being animated
        public static DependencyProperty TargetProperty = DependencyProperty.RegisterAttached("Target", typeof(DependencyObject), typeof(ThicknessAnimationX), null);
        public static DependencyProperty TargetPropertyProperty = DependencyProperty.RegisterAttached("TargetProperty", typeof(DependencyProperty), typeof(DependencyObject), null);

        public static readonly DependencyProperty FromProperty = DependencyProperty.RegisterAttached("From", typeof(Thickness), typeof(DoubleAnimation), null);
        public static readonly DependencyProperty ToProperty = DependencyProperty.RegisterAttached("To", typeof(Thickness), typeof(DoubleAnimation), null);

        public static void SetElement(DependencyObject o, DependencyObject value)
        {
            o.SetValue(ElementProperty, value);
        }

        public static DependencyObject GetElement(DependencyObject o)
        {
            return (DependencyObject)o.GetValue(ElementProperty);
        }

        private static void OnElementPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (e.NewValue != null)
            {
                DoubleAnimation doubleAnimation = (DoubleAnimation)d;

                doubleAnimation.SetValue(TargetProperty, e.NewValue);
                doubleAnimation.From = 0;
                doubleAnimation.To = 1;
                doubleAnimation.SetValue(TargetPropertyProperty, FrameworkElement.MarginProperty);
                Storyboard.SetTargetProperty(doubleAnimation, new PropertyPath("(ThicknessAnimationX.Time)"));
                Storyboard.SetTarget(doubleAnimation, doubleAnimation);
            }
        }


        private static void OnTimeChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            DoubleAnimation animation = (DoubleAnimation)sender;
            double time = GetTime(animation);
            Thickness from = (Thickness)sender.GetValue(FromProperty);
            Thickness to = (Thickness)sender.GetValue(ToProperty);
            DependencyProperty targetProperty = (DependencyProperty)sender.GetValue(TargetPropertyProperty);
            DependencyObject target = (DependencyObject)sender.GetValue(TargetProperty);
            target.SetValue(targetProperty, new Thickness((to.Left - from.Left) * time + from.Left,
                                                          (to.Top - from.Top) * time + from.Top,
                                                          (to.Right - from.Right) * time + from.Right,
                                                          (to.Bottom - from.Bottom) * time + from.Bottom));
        }

        public static double GetTime(DoubleAnimation animation)
        {
            return (double)animation.GetValue(TimeProperty);
        }

        public static void SetTime(DoubleAnimation animation, double value)
        {
            animation.SetValue(TimeProperty, value);
        }

        public static Thickness GetFrom(DoubleAnimation animation)
        {
            return (Thickness)animation.GetValue(FromProperty);
        }

        public static void SetFrom(DoubleAnimation animation, Thickness value)
        {
            animation.SetValue(FromProperty, value);
        }

        public static Thickness GetTo(DoubleAnimation animation)
        {
            return (Thickness)animation.GetValue(ToProperty);
        }

        public static void SetTo(DoubleAnimation animation, Thickness value)
        {
            animation.SetValue(ToProperty, value);
        }
    }   
}

And then you can do this in XAML

<VisualStateManager.VisualStateGroups>
    <VisualStateGroup x:Name="Positions">
        <VisualStateGroup.Transitions>
            <VisualTransition GeneratedDuration="0:0:0.2"/>
        </VisualStateGroup.Transitions>
        <VisualState x:Name="Left">                    
            <Storyboard>
                <DoubleAnimation Duration="0:0:0.3" NiceCards:ThicknessAnimationX.To="0,0,0,0" NiceCards:ThicknessAnimationX.Element="{Binding ElementName=rectangle1}" Storyboard.TargetName="rectangle1" Storyboard.TargetProperty="Opacity"/>
            </Storyboard>                       
        </VisualState>
        <VisualState x:Name="Right">                    
            <Storyboard>
                <DoubleAnimation Duration="0:0:0.3" NiceCards:ThicknessAnimationX.To="0,200,0,0" NiceCards:ThicknessAnimationX.Element="{Binding ElementName=rectangle1}" Storyboard.TargetName="rectangle1" Storyboard.TargetProperty="Opacity"/>
            </Storyboard>                    
        </VisualState>
    </VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Rectangle Height="100" HorizontalAlignment="Left" Margin="23,25,0,0" x:Name="rectangle1" Stroke="Black" StrokeThickness="1" VerticalAlignment="Top" Width="200" Fill="#FF1BAA00"/>

Note that if you don't set a Target property to a DoubleAnimation in XAML, you won't be able to display the control/page in Blend. To fix this, just add a fake target property (in the code above I added the opacity property which is a double value), And it will be overriden at runtime anyway

来源：https://stackoverflow.com/questions/1466288/animate-margin-change-in-silverlight