为什么在 xaml、WPF 中的 Style 中定义模板? [英] Why define a Template inside a Style in xaml, WPF?

问题描述

自从我开始使用 MS 的控件模板示例作为构建自定义控件的基础以来，我一直在想这个问题.

I've been wondering this ever since I started using MS's control templates examples as basis to build custom controls.

以标签为例:http://msdn.microsoft.com/en-us/library/ms752327.aspx

到底为什么是这样定义的:

why on earth is it defined like this:

<Style x:Key="{x:Type Label}" TargetType="Label">
  <Setter Property="HorizontalContentAlignment" Value="Left" />
  <Setter Property="VerticalContentAlignment" Value="Top" />
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="Label">
        <Border>
          <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                            VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                            RecognizesAccessKey="True" />
        </Border>
        <ControlTemplate.Triggers>
          <Trigger Property="IsEnabled" Value="false">
            <Setter Property="Foreground">
              <Setter.Value>
                <SolidColorBrush Color="{DynamicResource DisabledForegroundColor}" />
              </Setter.Value>
            </Setter>
          </Trigger>
        </ControlTemplate.Triggers>
      </ControlTemplate>
    </Setter.Value>
  </Setter>
</Style>

而不是直接这样:

<ControlTemplate x:Key="{x:Type Label}" TargetType="Label">
    <Border>
      <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                        VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                        RecognizesAccessKey="True" />
    </Border>
    <ControlTemplate.Triggers>
      <Trigger Property="IsEnabled" Value="false">
        <Setter Property="Foreground">
          <Setter.Value>
            <SolidColorBrush Color="{DynamicResource DisabledForegroundColor}" />
          </Setter.Value>
        </Setter>
      </Trigger>
    </ControlTemplate.Triggers>
</ControlTemplate>

然后直接作为模板调用而不是通过样式属性?

and then called as a template directly and not through the style property?

我不认为这样做有什么隐藏的原因吗?或者这只是一种做事方式，仅此而已?

is there a hidden reason I do not see for doing things like this? or is it just one way of doing things and that's it?

(注意:不要告诉我这是因为水平和垂直对齐设置器！我们都知道这些是标签的默认值，如果你保留这些值，这基本上没用)

(NB: don't tell me this is because of the horizontal and vertical alignment setters! we all know those are the default values for a label and this is basically useless if you keep those values)

推荐答案

如果不使用样式，就不可能自动将模板分配给特定控件类型的所有实例.为控件模板设置x:Key="{x:Type Label}"不会自动将此模板应用于Label类型的所有控件.

Without using a Style it's not possible to automatically assign the template to all instances of a specific control type. Setting x:Key="{x:Type Label}" for the control template does not automatically apply this template to all controls of type Label.

您可以通过将 TargetType 设置为 Button 来将样式应用于可视化树中声明下方的所有按钮，但是您不能使用模板，如果您没有将其包装在具有 Setter 模板的 Style 中.

You can make a style apply to all buttons below the declaration in the visual tree by setting the TargetType to Button, but you can't do the same with a template, if you do not wrap it inside a Style that have a Setter for the template.

另外，请注意，在您的示例中，您可以交换

Also, note that in your example you can exchange

<Style x:Key="{x:Type Label}" TargetType="Label">

与

<Style TargetType="Label">

如果 x:Key 定义被省略，x:Key 被设置为 TargetType.

As the x:Key is set to the TargetType if the x:Key definition is omitted.

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