您可以使用 ControlTemplate 来实现:
<Style x:Key="ButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Background" Value="Black"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Path Fill="{TemplateBinding Background}"
Data="M 0,0 A 100,100 90 0 0 100,100 L 100,100 100,0" />
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
比你将它应用到按钮上:
<Button Style="{StaticResource ButtonStyle}"/>
如果您需要一些参考来绘制“路径”,请查看this MSDN 链接。
更新
要显示内容,您应该使用 ContentPresenter,如下所示:
<Style x:Key="ButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Background" Value="Black"/>
<Setter Property="HorizontalAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Grid>
<Path Fill="{TemplateBinding Background}"
Data="M 0,0 A 100,100 90 0 0 100,100 L 100,100 100,0" />
<ContentPresenter VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
HorizontalAlignment="{TemplateBinding HorizontalAlignment}"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
在按钮中:
<Button Style="{StaticResource ButtonStyle}" Foreground="White">
test
</Button>