如何正确居中 WPF 画布？
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how to properly center a WPF canvas?
提问by Frank
I have a full screen dialog and want to center a canvas. It seems to work well with a grid with Vertical/Horizontalalignment for a Label for example, but when I try this the top left corner gets centered instead of the middle of the canvas:
我有一个全屏对话框，想将画布居中。例如，它似乎适用于带有垂直/水平对齐标签的网格，但是当我尝试此操作时，左上角居中而不是画布中间：
<Window
Title=""
Topmost="True" WindowStyle="None" WindowState="Maximized"
>
<Grid>
<Grid VerticalAlignment="Center" HorizontalAlignment="Center">
<Canvas>
<Border Margin="20"
Background="White"
BorderBrush="Black"
BorderThickness="2"
Padding="20" >
<DockPanel Margin="10">
<StackPanel DockPanel.Dock="Top" Margin="0 0 0 50"
Orientation="Vertical">
<Label FontSize="32" Content="Hello"></Label>
</StackPanel>
<StackPanel HorizontalAlignment="Right"
DockPanel.Dock="Bottom"
Orientation="Horizontal">
<Label FontSize="32" Content="Hello"></Label>
</StackPanel>
</DockPanel>
</Border>
</Canvas>
</Grid>
回答by K Mehta
That's because you haven't set a Width and Height on your canvas, and in in the case of a canvas, the ActualWidth and ActualHeight properties (which are used for layout) default to 0.
那是因为您没有在画布上设置 Width 和 Height，对于画布，ActualWidth 和 ActualHeight 属性（用于布局）默认为 0。
You can test this by setting the Background on the Canvas - in your case, the background color won't be rendered because of the aforementioned reason.
您可以通过在画布上设置背景来测试这一点 - 在您的情况下，由于上述原因，背景颜色不会被渲染。
To work around this do one of the following:
要解决此问题，请执行以下操作之一：
- pick another container (Grid, for example) which adapts based on it's children's sizes
- set the Width and Height on the Canvas explicitly.
- 选择另一个容器（例如网格），它根据孩子的大小进行调整
- 明确设置画布上的宽度和高度。
回答by Tony
You can put the Border as child of Grid instead of Canvas. (The Grid can have more than one child) Try this:
您可以将 Border 作为 Grid 的子项而不是 Canvas。（网格可以有多个孩子）试试这个：
<Window
Title=""
Topmost="True" WindowStyle="None" WindowState="Maximized"
>
<Grid>
<Canvas HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<Rectangle Canvas.Left="40" Canvas.Top="31" Width="630" Height="41" Fill="Blue" />
<Ellipse Canvas.Left="130" Canvas.Top="79" Width="580" Height="580" Fill="Blue" />
<Path Canvas.Left="61" Canvas.Top="28" Width="133" Height="98" Fill="Blue" Stretch="Fill" Data="M61,325 L293,28" />
</Canvas>
<Border Margin="20"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Background="WhiteSmoke"
BorderBrush="Black"
BorderThickness="2"
Padding="20">
<DockPanel Margin="10">
<StackPanel DockPanel.Dock="Top" Margin="0 0 0 50" Orientation="Vertical">
<Label FontSize="32" Content="Hello" />
</StackPanel>
<StackPanel HorizontalAlignment="Right"
DockPanel.Dock="Bottom"
Orientation="Horizontal">
<Label FontSize="32" Content="Hello" />
</StackPanel>
</DockPanel>
</Border>
</Grid>
</Window>
