WPF中自訂GridLengthAnimation的執行個體教程

這篇文章主要為大家詳細介紹了WPF中自訂GridLengthAnimation的相關資料，具有一定的參考價值，感興趣的小夥伴們可以參考一下

需求

我們想在編輯一個列表中某一個條目時，將編輯的詳情內容也放置當前面，比如右側。

可以通過將一個Grid,分成兩個Cloumn,動態調整兩個Cloumn的Width，就可以實現這個需求。

我們知道，Clomun的Width是個，而預設的動畫沒有這樣子的。我們就需要自己實現這樣一人動畫。

設計
我們從Animation的類圖上看到

我們可以從需求

我們想在編輯一個列表中某一個條目時，將編輯的詳情內容也放置當前面，比如右側。

可以通過將一個Grid,分成兩個Cloumn,動態調整兩個Cloumn的Width，就可以實現這個需求。

我們知道，Clomun的Width是個GridLength，而預設的動畫沒有這樣子的。我們就需要自己實現這樣一人動畫。

設計

我們從Animation的類圖上看到AnimationTimeline繼承，重寫其GetCurrentValue

public class GridLengthAnimation : AnimationTimeline  {    /// <summary>    /// Returns the type of object to animate    /// </summary>    public override Type TargetPropertyType => typeof(GridLength);     /// <summary>    /// Creates an instance of the animation object    /// </summary>    /// <returns>Returns the instance of the GridLengthAnimation</returns>    protected override System.Windows.Freezable CreateInstanceCore()    {      return new GridLengthAnimation();    }     /// <summary>    /// Dependency property for the From property    /// </summary>    public static readonly DependencyProperty FromProperty = DependencyProperty.Register("From", typeof(GridLength),      typeof(GridLengthAnimation));     /// <summary>    /// CLR Wrapper for the From depenendency property    /// </summary>    public GridLength From    {      get      {        return (GridLength)GetValue(GridLengthAnimation.FromProperty);      }      set      {        SetValue(GridLengthAnimation.FromProperty, value);      }    }     /// <summary>    /// Dependency property for the To property    /// </summary>    public static readonly DependencyProperty ToProperty = DependencyProperty.Register("To", typeof(GridLength),      typeof(GridLengthAnimation));     /// <summary>    /// CLR Wrapper for the To property    /// </summary>    public GridLength To    {      get      {        return (GridLength)GetValue(GridLengthAnimation.ToProperty);      }      set      {        SetValue(GridLengthAnimation.ToProperty, value);      }    }     /// <summary>    /// Animates the grid let set    /// </summary>    /// <param name="defaultOriginValue">The original value to animate</param>    /// <param name="defaultDestinationValue">The final value</param>    /// <param name="animationClock">The animation clock (timer)</param>    /// <returns>Returns the new grid length to set</returns>    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);    }

如上所示，我們仿著預設動畫實現了From,To,同時將其屬性定義為GridLength,當動畫執行時，我們重寫了GetCurrentValue,使其根據From/To屬性相關聯。

最佳化

通過以上代碼，我們實現了在GridLength變化時，實現動畫。但是，試用後我們發現，動畫，有點太線性。這個時候，怎麼辦？

可以通過引入EasingFunction來實現。我們知道EasingFunction其實就是一個與時間t有關的時間函數f(t).通過時間函數的處理，我們使動畫過渡不要那麼線性。

 /// <summary>    /// The <see cref="EasingFunction" /> dependency property's name.    /// </summary>    public const string EasingFunctionPropertyName = "EasingFunction";     /// <summary>    /// Gets or sets the value of the <see cref="EasingFunction" />    /// property. This is a dependency property.    /// </summary>    public IEasingFunction EasingFunction    {      get      {        return (IEasingFunction)GetValue(EasingFunctionProperty);      }      set      {        SetValue(EasingFunctionProperty, value);      }    }     /// <summary>    /// Identifies the <see cref="EasingFunction" /> dependency property.    /// </summary>    public static readonly DependencyProperty EasingFunctionProperty = DependencyProperty.Register(      EasingFunctionPropertyName,      typeof(IEasingFunction),      typeof(GridLengthAnimation),      new UIPropertyMetadata(null));

對應的，還要重寫GetCurrentValue函數。

public override object GetCurrentValue(object defaultOriginValue,      object defaultDestinationValue, AnimationClock animationClock)    {      double fromVal = ((GridLength)GetValue(FromProperty)).Value;       double toVal = ((GridLength)GetValue(ToProperty)).Value;       //check that from was set from the caller      //if (fromVal == 1)      //  //set the from as the actual value      //  fromVal = ((GridLength)defaultDestinationValue).Value;       double progress = animationClock.CurrentProgress.Value;       IEasingFunction easingFunction = EasingFunction;      if (easingFunction != null)      {        progress = easingFunction.Ease(progress);      }        if (fromVal > toVal)        return new GridLength((1 - progress) * (fromVal - toVal) + toVal, GridUnitType.Star);         return new GridLength(progress * (toVal - fromVal) + fromVal, GridUnitType.Star);    }

使用

 <anim:GridLengthAnimation Storyboard.TargetProperty="Width" From="0" To="*" Duration="0:0:0.5"/>

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