所以你想根据切换按钮的IsChecked属性更改内容，对吗？如果是这样，你不需要设置模板，你可以使用简单的数据绑定来实现。

首先，你需要为数据绑定创建一个值转换器，它可以将 bool 值转换为 Segoe MDL2 Assets 图标。

像这样：

 public class DateFormatter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        bool ischecked = (bool)value;

        string content =null;

        if (ischecked)
        {
            //the button is checked
            content = "\xE762";
        }
        else 
        {
            //the button is unchecked
            content = "\xE759";
        }

        return content;
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

之后，你需要在 xaml 代码中设置绑定。

像这样：

 <Page.Resources>
    
    <local:DateFormatter x:Key="MyValueConverter"/>
    
</Page.Resources>

<Grid>
    <ToggleButton x:Name="MyToggleButton"  Content="{Binding ElementName=MyToggleButton, Path=IsChecked, Mode=OneWay, Converter={StaticResource MyValueConverter}}" IsChecked="True" FontFamily="Segoe MDL2 Assets" />
</Grid>

现在，当你选中或取消选中切换按钮时，图标将根据需要更改。

更多信息请参考：IValueConverter 接口和值转换器

更新

我建议使用数据绑定的原因是以后更容易更改图标值。

如果你必须使用visualstate，也可以这样做。你需要先创建 ToggleButton 的默认样式。Document Outline在 VS 中打开窗口，右键单击你添加到 XAML 的 ToggleButton，将鼠标移至Edit a template，然后选择Edit a Copy。

然后你可以找到名为Checked, CheckedPointerOver,的视觉状态CheckedPressed。对这些状态再添加一项更改，如下所示：

 <VisualState x:Name="Checked">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Background">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonBackgroundChecked}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonForegroundChecked}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="BorderBrush">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonBorderBrushChecked}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Content">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="&#xE759;"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <PointerUpThemeAnimation Storyboard.TargetName="ContentPresenter"/>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="CheckedPointerOver">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Background">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonBackgroundCheckedPointerOver}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="BorderBrush">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonBorderBrushCheckedPointerOver}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonForegroundCheckedPointerOver}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Content">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="&#xE759;"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <PointerUpThemeAnimation Storyboard.TargetName="ContentPresenter"/>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="CheckedPressed">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Background">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonBackgroundCheckedPressed}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonForegroundCheckedPressed}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="BorderBrush">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonBorderBrushCheckedPressed}"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Content">
                                            <DiscreteObjectKeyFrame KeyTime="0" Value="&#xE759;"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <PointerDownThemeAnimation Storyboard.TargetName="ContentPresenter"/>
                                    </Storyboard>
                                </VisualState>

如你所见，我现在添加了这些状态的内容更改，你可以在选中ToggleButton时看到你想要在ToggleButton中显示的图标。