[答网友问]让GridLength支持动画

                        [答网友问]WPF中让GridLength类型支持动画
                                                               周银辉

今天一位收到网友求助:
"你好！我想向你请教关于动画的问题:比如，一个Page分为上、下l两块，我想通过动画实现分别隐藏某块的内容，当我触发一个按钮的Click事件时，实现隐藏上面的面板，同时下的面板就要延伸并占据上面面板的空间，这个过程到好实现，问题是我如果第二次触发这个按钮的Click事件时，怎么才能让上面的面板出现（恢复原始大小）并且下面的面板的大小也回到原始大小"

对于这个问题,有一个很好的解决方法是,将两个面板放到Grid中,并让GridLength类型支持动画,就像Double类型有着对应的DoubleAnimation一样.这样就将网友的问题转化为:上面的面板所在行对应RowDefinition的高度由0.5变为0,再由0变为0.5(单位GridUnitType.Star)

以下是GridLengthAnimation类的完整代码,你可以使用她就像使用DoubleAnimaion一样.

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Media.Animation;
using System.Windows;
using System.Diagnostics;

namespace GridAnimationDemo
{
    internal class GridLengthAnimation : AnimationTimeline
    {
        
        public static readonly DependencyProperty FromProperty;
        public static readonly DependencyProperty ToProperty;
       

        static GridLengthAnimation()
        {
            FromProperty = DependencyProperty.Register("From", typeof(GridLength),
                typeof(GridLengthAnimation));

            ToProperty = DependencyProperty.Register("To", typeof(GridLength), 
                typeof(GridLengthAnimation));
        }

       
        public override Type TargetPropertyType
        {
            get 
            {
                return typeof(GridLength);
            }
        }

        protected override System.Windows.Freezable CreateInstanceCore()
        {
            return new GridLengthAnimation();
        }

        public override object GetCurrentValue(object defaultOriginValue, object defaultDestinationValue, AnimationClock animationClock)
        {
            double fromVal = ((GridLength)GetValue(GridLengthAnimation.FromProperty)).Value;
            double toVal = ((GridLength)GetValue(GridLengthAnimation.ToProperty)).Value;

            if (fromVal > toVal)
            {
                return new GridLength((1 - animationClock.CurrentProgress.Value) * (fromVal - toVal) + toVal, GridUnitType.Star);
            }
            else
                return new GridLength(animationClock.CurrentProgress.Value * (toVal - fromVal) + fromVal, GridUnitType.Star);
        }
      

        
        public GridLength From
        {
            get
            {
                return (GridLength)GetValue(GridLengthAnimation.FromProperty);
            }
            set
            {
                SetValue(GridLengthAnimation.FromProperty, value);
            }
        }

        public GridLength To
        {
            get
            {
                return (GridLength)GetValue(GridLengthAnimation.ToProperty);
            }
            set
            {
                SetValue(GridLengthAnimation.ToProperty, value);
            }
        }
      

    }
}

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