[答網友問]WPF中讓GridLength類型支持動畫
?????????????????????????????????????????????????????????????? 周銀輝

今天一位收到網友求助:
"你好！我想向你請教關于動畫的問題:比如，一個Page分為上、下l兩塊，我想通過動畫實現分別隱藏某塊的內容，當我觸發一個按鈕的Click事件時，實現隱藏上面的面板，同時下的面板就要延伸并占據上面面板的空間，這個過程到好實現，問題是我如果第二次觸發這個按鈕的Click事件時，怎么才能讓上面的面板出現（恢復原始大小）并且下面的面板的大小也回到原始大小"

對于這個問題,有一個很好的解決方法是,將兩個面板放到Grid中,并讓GridLength類型支持動畫,就像Double類型有著對應的DoubleAnimation一樣.這樣就將網友的問題轉化為:上面的面板所在行對應RowDefinition的高度由0.5變為0,再由0變為0.5(單位GridUnitType.Star)

以下是GridLengthAnimation類的完整代碼,你可以使用她就像使用DoubleAnimaion一樣.
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);
????????????}
????????}
??????

????}
}

下載Demo

?

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