Blend_技巧篇_淡入淡出

1、實現原理

1.1 利用UIElement.OpacityMask屬性，用於改變對象區域的不透明度的畫筆。可以使元素的特定區域透明或部分透明，從而實現比較新穎的效果。

1.2 OpacityMask屬性接受任何畫刷，可利用LinearGradientBrush線性漸變畫刷，通過對漸變畫刷中各顏色點加以動畫處理即可。

2、漸變淡入實現

漸變淡入效果，可通過事件觸發器觸發Loaded事件實現，所以可以僅用前端XAML語言實現。

2.1 設置對象的OpacityMask屬性

 

<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 設置對象的事件觸發器

 

<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、漸變淡出實現

漸變淡出效果，由於事件觸發器事件需要路由事件觸發，所以需要使用後端代碼實現。

3.1 準備漸變淡出的動畫和畫刷資源

 

<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 後端通過綁定按鈕的Click事件實現

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();
}