本文将介绍一个好玩但实际作用可能不太大的动画效果：跳动的字符。为了提高动画效果的可重用性以及调用的灵活性，通过Behavior实现跳动的字符动画。先看下效果：
通过TextEffect的PositionStart和PositionCount属性控制应用动画效果的子字符串的起始位置以及长度，同时使用TranslateTransform设置字符纵坐标的移动变换，以实现跳动的效果。主要步骤如下：
Loaded事件，在Load事件中为TextBlock添加TextEffect效果，其中PositionCount设置为1，每次只跳动一个字符。BeginEffect方法，并创建控制子字符纵向移动变换的线性动画。然后根据字符串（剔除空字符）的长度n，创建n个关键帧，每个关键帧中把PositionStart设置为要跳动的字符在字符串中的索引IsEnabled=true和TextBlock内容变化时,启动动画效果在创建关键帧设置跳动字符位置时剔除了空字符，是为了是动画效果显得连贯
public class DanceCharEffectBehavior : Behavior<TextBlock>
{
private TextEffect _textEffect;
private string _textEffectName;
private TranslateTransform _translateTransform = null;
private string _translateTransformName;
private Storyboard _storyboard;
protected override void OnAttached()
{
base.OnAttached();
this.AssociatedObject.Loaded += AssociatedObject_Loaded;
this.AssociatedObject.Unloaded += AssociatedObject_Unloaded;
this.AssociatedObject.IsVisibleChanged += AssociatedObject_IsVisibleChanged;
BindingOperations.SetBinding(this, DanceCharEffectBehavior.InternalTextProperty, new Binding("Text") { Source = this.AssociatedObject });
}
protected override void OnDetaching()
{
base.OnDetaching();
this.AssociatedObject.Loaded -= AssociatedObject_Loaded;
this.AssociatedObject.Unloaded -= AssociatedObject_Unloaded;
this.AssociatedObject.IsVisibleChanged -= AssociatedObject_IsVisibleChanged;
this.ClearValue(DanceCharEffectBehavior.InternalTextProperty);
if (_storyboard != null)
{
_storyboard.Remove(this.AssociatedObject);
_storyboard.Children.Clear();
}
if (_textEffect != null)
this.AssociatedObject.TextEffects.Remove(_textEffect);
}
private void AssociatedObject_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
{
if ((bool)e.NewValue == false)
{
if (_storyboard != null)
_storyboard.Stop(this.AssociatedObject);
}
else
{
BeginEffect(this.AssociatedObject.Text);
}
}
private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
{
if (_textEffect == null)
{
this.AssociatedObject.TextEffects.Add(_textEffect = new TextEffect()
{
PositionCount = 1,
Transform = _translateTransform = new TranslateTransform(),
});
NameScope.SetNameScope(this.AssociatedObject, new NameScope());
this.AssociatedObject.RegisterName(_textEffectName = "n" + Guid.NewGuid().ToString("N"), _textEffect);
this.AssociatedObject.RegisterName(_translateTransformName = "n" + Guid.NewGuid().ToString("N"), _translateTransform);
if (IsEnabled)
BeginEffect(this.AssociatedObject.Text);
}
}
private void AssociatedObject_Unloaded(object sender, RoutedEventArgs e)
{
StopEffect();
}
private void SetEffect(string text)
{
if (string.IsNullOrEmpty(text) || this.AssociatedObject.IsLoaded == false)
{
StopEffect();
return;
}
BeginEffect(text);
}
private void StopEffect()
{
if (_storyboard != null)
{
_storyboard.Stop(this.AssociatedObject);
}
}
private void BeginEffect(string text)
{
StopEffect();
int textLength = text.Length;
if (textLength < 1 || _translateTransformName == null || IsEnabled == false) return;
if (_storyboard == null)
_storyboard = new Storyboard();
double duration = 0.5d;
DoubleAnimation da = new DoubleAnimation();
Storyboard.SetTargetName(da, _translateTransformName);
Storyboard.SetTargetProperty(da, new PropertyPath(TranslateTransform.YProperty));
da.From = 0d;
da.To = 10d;
da.Duration = TimeSpan.FromSeconds(duration / 2d);
da.RepeatBehavior = RepeatBehavior.Forever;
da.AutoReverse = true;
char emptyChar = ' ';
List<int> lsb = new List<int>();
for (int i = 0; i < textLength; ++i)
{
if (text[i] != emptyChar)
{
lsb.Add(i);
}
}
Int32AnimationUsingKeyFrames frames = new Int32AnimationUsingKeyFrames();
Storyboard.SetTargetName(frames, _textEffectName);
Storyboard.SetTargetProperty(frames, new PropertyPath(TextEffect.PositionStartProperty));
frames.Duration = TimeSpan.FromSeconds((lsb.Count) * duration);
frames.RepeatBehavior = RepeatBehavior.Forever;
frames.AutoReverse = true;
int ii = 0;
foreach (int index in lsb)
{
frames.KeyFrames.Add(new DiscreteInt32KeyFrame()
{
Value = index,
KeyTime = TimeSpan.FromSeconds(ii * duration),
});
++ii;
}
_storyboard.Children.Add(da);
_storyboard.Children.Add(frames);
_storyboard.Begin(this.AssociatedObject, true);
}
private string InternalText
{
get { return (string)GetValue(InternalTextProperty); }
set { SetValue(InternalTextProperty, value); }
}
private static readonly DependencyProperty InternalTextProperty =
DependencyProperty.Register("InternalText", typeof(string), typeof(DanceCharEffectBehavior),
new PropertyMetadata(OnInternalTextChanged));
private static void OnInternalTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var source = d as DanceCharEffectBehavior;
if (source._storyboard != null)
{
source._storyboard.Stop(source.AssociatedObject);
source._storyboard.Children.Clear();
}
source.SetEffect(e.NewValue == null ? string.Empty : e.NewValue.ToString());
}
public bool IsEnabled
{
get { return (bool)GetValue(IsEnabledProperty); }
set { SetValue(IsEnabledProperty, value); }
}
public static readonly DependencyProperty IsEnabledProperty =
DependencyProperty.Register("IsEnabled", typeof(bool), typeof(DanceCharEffectBehavior), new PropertyMetadata(true, (d, e) =>
{
bool b = (bool)e.NewValue;
var source = d as DanceCharEffectBehavior;
source.SetEffect(source.InternalText);
}));
}
调用的时候只需要在TextBlock添加Behavior即可，代码如下
<TextBlock FontSize="20" Text="Hello">
<i:Interaction.Behaviors>
<local:DanceCharEffectBehavior x:Name="titleEffect" IsEnabled="True" />
</i:Interaction.Behaviors>
</TextBlock>
本例中还有许多可以完善的地方，比如字符跳动的幅度可以根据实际的FontSize来设置，或者增加依赖属性来控制；动画是否倒退播放，是否循环播放，以及动画的速度都可以通过增加依赖属性在调用时灵活设置。
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