1、实现原理
1.1 利用UIElement.OpacityMask属性，用于改变对象区域的不透明度的画笔。可以使元素的特定区域透明或部分透明，从而实现比较新颖的效果。
1.2 OpacityMask属性接受任何画刷，可利用LinearGradientBrush线性渐变画刷，通过对渐变画刷中各颜色点加以动画处理即可。
2、渐变淡入实现
渐变淡入效果，可通过事件触发器触发Loaded事件实现，所以可以仅用前端XAML语言实现。
2.1 设置对象的OpacityMask属性
<Grid.OpacityMask> <LinearGradientBrush StartPoint="0.5,1" EndPoint="0.5,0"> <GradientStop Color="#00000000" Offset="0"/> <GradientStop Color="#00000000" Offset="1"/> <GradientStop Color="#00000000" Offset="1"/> </LinearGradientBrush> </Grid.OpacityMask>
2.2 设置对象的事件触发器
<Grid.Triggers> <EventTrigger RoutedEvent="Loaded"> <EventTrigger.Actions> <BeginStoryboard> <Storyboard> <DoubleAnimation From="1" To="0" Duration="0:0:1.5" Storyboard.TargetProperty="OpacityMask.(GradientBrush.GradientStops)[1].Offset"/> <DoubleAnimation From="1" To="0" Duration="0:0:1" BeginTime="0:0:0.5" Storyboard.TargetProperty="OpacityMask.(GradientBrush.GradientStops)[2].Offset"/> <ColorAnimation To="#FF000000" Duration="0" Storyboard.TargetProperty="OpacityMask.(GradientBrush.GradientStops)[2].Color"/> </Storyboard> </BeginStoryboard> </EventTrigger.Actions> </EventTrigger> </Grid.Triggers>
3、渐变淡出实现
渐变淡出效果，由于事件触发器事件需要路由事件触发，所以需要使用后端代码实现。
3.1 准备渐变淡出的动画和画刷资源
<Window.Resources> <Storyboard x:Key="ClosedStoryboard" Storyboard.TargetName="LoginGrid"> <DoubleAnimation From="1" To="0" Duration="0:0:2" Storyboard.TargetProperty="OpacityMask.(GradientBrush.GradientStops)[1].Offset"/> <DoubleAnimation From="1" To="0" Duration="0:0:1.5" BeginTime="0:0:0.5"Storyboard.TargetProperty="OpacityMask.(GradientBrush.GradientStops)[2].Offset"/> <ColorAnimation To="#00000000" Duration="0" Storyboard.TargetProperty="OpacityMask.(GradientBrush.GradientStops)[2].Color"/> </Storyboard> <LinearGradientBrush x:Key="ClosedBrush" StartPoint="0.5,0" EndPoint="0.5,1"> <GradientStop Color="#FF000000" Offset="0"/> <GradientStop Color="#FF000000" Offset="1"/> <GradientStop Color="#FF000000" Offset="1"/> </LinearGradientBrush> </Window.Resources>
3.2 后端通过绑定按钮的Click事件实现
private void btnCancel_Click(object sender, RoutedEventArgs e) { this.IsEnabled = false; LoginGrid.OpacityMask = this.Resources["ClosedBrush"] as LinearGradientBrush; Storyboard std = this.Resources["ClosedStoryboard"] as Storyboard; std.Completed += delegate { this.Close(); }; std.Begin(); }
4、运行效果