WPF 控件模板：为什么指定没有 ColumnDefinations/RowDefinations 的 Grid 作为外部元素？
我一直在阅读《WPF 编程》，这是有关控制模板的示例之一：
<Button DockPanel.Dock="Bottom" x:Name="addButton" Content="Add">
<Button.Template>
<ControlTemplate TargetType="{x:Type Button}">
<Grid>
<Ellipse Width="128" Height="32" Fill="Yellow" Stroke="Black" />
<ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center" />
</Grid>
</ControlTemplate>
</Button.Template>
</Button>
我想知道为什么使用网格而不是更简单的面板（例如画布）？因为我们没有贴花任何行/列？
谢谢！
I've been reading Programming WPF, here is one of the examples about Control Template:
<Button DockPanel.Dock="Bottom" x:Name="addButton" Content="Add">
<Button.Template>
<ControlTemplate TargetType="{x:Type Button}">
<Grid>
<Ellipse Width="128" Height="32" Fill="Yellow" Stroke="Black" />
<ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center" />
</Grid>
</ControlTemplate>
</Button.Template>
</Button>
I'm wondering why use a grid but not a simpler panel such as canvas? Since we didn't decalre any row/columns?
Thanks!
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如果您未指定任何行或列，则每一行或列之一都是隐式的，因此为您提供一个网格单元格。因此，
Ellipse和ContentPresenter占据相同的网格单元。添加到同一单元格的项目的 z 顺序由它们添加的顺序决定。在这种情况下，ContentPresenter将出现在Ellipse的“顶部”。如果您使用
Canvas而不是Grid，子级的大小将不受容器大小的限制。这是因为Canvas不会像Grid那样对其子级施加任何大小限制。因此，您必须指定Ellipse和ContentPresenter的大小，并且您需要知道Canvas的大小设置该大小。因此，使用Grid会更容易、更直观。If you don't specify any rows or columns, one of each is implicit, therefore giving you a single grid cell. Thus, both the
EllipseandContentPresenteroccupy the same grid cell. The z-order of items added to the same cell is determined by the order in which they are added. In this case, theContentPresenterwill appear "on top of" theEllipse.Were you to to use a
Canvasinstead of aGrid, the size of the children would not be restricted by the size of the container. That's because aCanvasdoes not impose any size restraints on its children like theGriddoes. Therefore, you'd have to specify a size for both theEllipseandContentPresenter, and you'd need to know the size of theCanvasto set that size. Ergo, it's just a whole lot easier and more intuitive using aGrid.