您可以通过LinearGradientBrush为您的Stroke. 像这样的东西:
<Line.Stroke>
<LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
<LinearGradientBrush.GradientStops>
<GradientStopCollection>
<GradientStop Color="Black" Offset="0.2"/>
<GradientStop Color="Transparent" Offset="0.201"/>
<GradientStop Color="Transparent" Offset="0.799"/>
<GradientStop Color="Black" Offset="0.8"/>
</GradientStopCollection>
</LinearGradientBrush.GradientStops>
</LinearGradientBrush>
</Line.Stroke>
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您还应该将线条的Height和设置StrokeThickness为相同的值,以确保显示整个渐变。