我看到你在使用MahApps.MetroWindow时，通过Blend的「编辑模板→编辑副本」功能生成Button模板后，遇到了讨厌的空引用异常，这确实是Blend处理MahApps自定义控件时的常见问题，我来帮你搞定它！

问题根源 #

Blend在生成模板时，没有正确识别MahApps为控件扩展的附加属性，导致模板里的部分绑定路径不完整，触发了空引用。具体来说是这两处绑定错误：

• ClipBorder的CornerRadius直接写了{TemplateBinding}，没有绑定到MahApps的附加属性mah:ControlsHelper.CornerRadius
• ContentControlEx的RecognizesAccessKey同样漏写了属性名，直接用{TemplateBinding}导致绑定失效

具体修复步骤 #

1. 修复CornerRadius绑定

把模板里两个ClipBorder的CornerRadius绑定替换为：

CornerRadius="{Binding Path=(mah:ControlsHelper.CornerRadius), RelativeSource={RelativeSource TemplatedParent}}"

因为MahApps是通过ControlsHelper.CornerRadius附加属性来设置Button的圆角，不是Button自身的CornerRadius属性，所以必须指定正确的附加属性路径。

2. 修复RecognizesAccessKey绑定

把ContentControlEx的RecognizesAccessKey属性从{TemplateBinding}改为：

RecognizesAccessKey="{TemplateBinding RecognizesAccessKey}"

这里Blend只是漏写了要绑定的属性名，补上就好。

3. （更省心的方案）基于MahApps默认样式修改

其实你不用重写整个模板，MahApps的控件都有现成的完整样式，直接基于默认样式扩展会更简单，还能避免绑定错误：

<Style x:Key="ButtonStyle1" TargetType="{x:Type Button}" BasedOn="{StaticResource MahApps.Styles.Button}">
    <!-- 只写你需要自定义的Setter，比如修改背景、圆角等 -->
    <Setter Property="Background" Value="{DynamicResource MahApps.Brushes.Gray10}"/>
    <Setter Property="mah:ControlsHelper.CornerRadius" Value="5"/>
</Style>

这种方式会继承所有MahApps的默认绑定、触发器和资源，不用手动维护复杂的模板代码。

修复后的完整ButtonStyle代码 #

这里给你贴出修正后的完整模板代码，替换你原来的ButtonStyle1即可：

<Style x:Key="ButtonStyle1" TargetType="{x:Type Button}">
    <Setter Property="Background" Value="{DynamicResource MahApps.Brushes.Gray10}"/>
    <Setter Property="BorderBrush" Value="{DynamicResource MahApps.Brushes.Button.Border}"/>
    <Setter Property="BorderThickness" Value="1"/>
    <Setter Property="FontFamily" Value="{DynamicResource MahApps.Fonts.Family.Button}"/>
    <Setter Property="FontSize" Value="{DynamicResource MahApps.Font.Size.Button}"/>
    <Setter Property="FontWeight" Value="Bold"/>
    <Setter Property="Foreground" Value="{DynamicResource MahApps.Brushes.ThemeForeground}"/>
    <Setter Property="MinHeight" Value="25"/>
    <Setter Property="Padding" Value="5 6"/>
    <Setter Property="SnapsToDevicePixels" Value="True"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <Grid>
                    <mah:ClipBorder x:Name="Border" 
                                    Background="{TemplateBinding Background}" 
                                    BorderBrush="{TemplateBinding BorderBrush}" 
                                    BorderThickness="{TemplateBinding BorderThickness}" 
                                    CornerRadius="{Binding Path=(mah:ControlsHelper.CornerRadius), RelativeSource={RelativeSource TemplatedParent}}" 
                                    SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                    <mah:ClipBorder x:Name="DisabledVisualElement" 
                                    Background="{DynamicResource MahApps.Brushes.Control.Disabled}" 
                                    CornerRadius="{Binding Path=(mah:ControlsHelper.CornerRadius), RelativeSource={RelativeSource TemplatedParent}}" 
                                    IsHitTestVisible="False" 
                                    Opacity="0" 
                                    SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                    <mah:ContentControlEx x:Name="PART_ContentPresenter" 
                                         ContentCharacterCasing="{Binding (mah:ControlsHelper.ContentCharacterCasing), RelativeSource={RelativeSource Mode=TemplatedParent}}" 
                                         ContentStringFormat="{TemplateBinding ContentStringFormat}" 
                                         ContentTemplate="{TemplateBinding ContentTemplate}" 
                                         Content="{TemplateBinding Content}" 
                                         ContentTemplateSelector="{TemplateBinding ContentTemplateSelector}" 
                                         HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" 
                                         Margin="{TemplateBinding BorderThickness}" 
                                         Padding="{TemplateBinding Padding}" 
                                         RecognizesAccessKey="{TemplateBinding RecognizesAccessKey}" 
                                         SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" 
                                         VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                </Grid>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Background" TargetName="Border" Value="{DynamicResource MahApps.Brushes.Gray8}"/>
                        <Setter Property="BorderBrush" TargetName="Border" Value="{Binding (mah:ControlsHelper.MouseOverBorderBrush), Mode=OneWay, RelativeSource={RelativeSource Mode=TemplatedParent}}"/>
                    </Trigger>
                    <Trigger Property="IsPressed" Value="True">
                        <Setter Property="Background" TargetName="Border" Value="{DynamicResource MahApps.Brushes.Gray7}"/>
                    </Trigger>
                    <Trigger Property="IsKeyboardFocusWithin" Value="True">
                        <Setter Property="BorderBrush" TargetName="Border" Value="{Binding (mah:ControlsHelper.FocusBorderBrush), Mode=OneWay, RelativeSource={RelativeSource Mode=TemplatedParent}}"/>
                        <Setter Property="BorderThickness" TargetName="Border" Value="{Binding (mah:ControlsHelper.FocusBorderThickness), Mode=OneWay, RelativeSource={RelativeSource Mode=TemplatedParent}}"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="False">
                        <Setter Property="Opacity" TargetName="DisabledVisualElement" Value="0.7"/>
                        <Setter Property="Opacity" TargetName="PART_ContentPresenter" Value="0.3"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
    <Setter Property="mah:ControlsHelper.ContentCharacterCasing" Value="Upper"/>
    <Setter Property="mah:ControlsHelper.CornerRadius" Value="3"/>
    <Setter Property="mah:ControlsHelper.FocusBorderBrush" Value="{DynamicResource MahApps.Brushes.Button.Border.Focus}"/>
    <Setter Property="mah:ControlsHelper.FocusBorderThickness" Value="2"/>
    <Setter Property="mah:ControlsHelper.MouseOverBorderBrush" Value="{DynamicResource MahApps.Brushes.Button.Border.MouseOver}"/>
</Style>

小提示 #

以后用Blend编辑MahApps控件的模板时，一定要重点检查附加属性的绑定，MahApps大量使用附加属性来扩展控件功能，Blend经常无法自动识别这些属性，容易生成不完整的绑定，这时候手动补全或者直接基于默认样式修改会更高效哦！