如何使用WPF中自定義GridLengthAnimation

如何使用WPF中自定義GridLengthAnimation？很多新手對(duì)此不是很清楚，為了幫助大家解決這個(gè)難題，下面小編將為大家詳細(xì)講解，有這方面需求的人可以來(lái)學(xué)習(xí)下，希望你能有所收獲。

需求

我們想在編輯一個(gè)列表中某一個(gè)條目時(shí)，將編輯的詳情內(nèi)容也放置當(dāng)前面，比如右側(cè)。

可以通過(guò)將一個(gè)Grid,分成兩個(gè)Cloumn,動(dòng)態(tài)調(diào)整兩個(gè)Cloumn的Width，就可以實(shí)現(xiàn)這個(gè)需求。

我們知道，Clomun的Width是個(gè)，而默認(rèn)的動(dòng)畫(huà)沒(méi)有這樣子的。我們就需要自己實(shí)現(xiàn)這樣一人動(dòng)畫(huà)。

設(shè)計(jì)
我們從Animation的類(lèi)圖上看到

我們可以從需求

我們想在編輯一個(gè)列表中某一個(gè)條目時(shí)，將編輯的詳情內(nèi)容也放置當(dāng)前面，比如右側(cè)。

可以通過(guò)將一個(gè)Grid,分成兩個(gè)Cloumn,動(dòng)態(tài)調(diào)整兩個(gè)Cloumn的Width，就可以實(shí)現(xiàn)這個(gè)需求。

我們知道，Clomun的Width是個(gè)GridLength，而默認(rèn)的動(dòng)畫(huà)沒(méi)有這樣子的。我們就需要自己實(shí)現(xiàn)這樣一人動(dòng)畫(huà)。

設(shè)計(jì)

我們從Animation的類(lèi)圖上看到AnimationTimeline繼承，重寫(xiě)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，我們仿著默認(rèn)動(dòng)畫(huà)實(shí)現(xiàn)了From,To,同時(shí)將其屬性定義為GridLength,當(dāng)動(dòng)畫(huà)執(zhí)行時(shí)，我們重寫(xiě)了GetCurrentValue,使其根據(jù)From/To屬性相關(guān)聯(lián)。

優(yōu)化

通過(guò)以上代碼，我們實(shí)現(xiàn)了在GridLength變化時(shí)，實(shí)現(xiàn)動(dòng)畫(huà)。但是，試用后我們發(fā)現(xiàn)，動(dòng)畫(huà)，有點(diǎn)太線性。這個(gè)時(shí)候，怎么辦？

可以通過(guò)引入EasingFunction來(lái)實(shí)現(xiàn)。我們知道EasingFunction其實(shí)就是一個(gè)與時(shí)間t有關(guān)的時(shí)間函數(shù)f(t).通過(guò)時(shí)間函數(shù)的處理，我們使動(dòng)畫(huà)過(guò)渡不要那么線性。

 /// <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(duì)應(yīng)的，還要重寫(xiě)GetCurrentValue函數(shù)。

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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