我如何在触发器中更改按钮内容前景？

Question

我想在按下按钮时从触发器更改前景，这是我到目前为止的XAML：

   <Window.Resources>
    <SolidColorBrush x:Key="FocuseBorder" Color="DarkBlue" ></SolidColorBrush>
    <SolidColorBrush x:Key="OverBorder" Color="Blue" />
    <SolidColorBrush x:Key="PressdBorder" Color="Red" />
    <SolidColorBrush  x:Key="DefulateBorder" Color="Black" ></SolidColorBrush>


    <LinearGradientBrush x:Key="GradDefulat" StartPoint="0.5,0" EndPoint="0.5,1">
        <GradientStop Color="#FF949494" Offset="0"/>
        <GradientStop Color="Black" Offset="1"/>
    </LinearGradientBrush>


    <LinearGradientBrush x:Key="GradOver" StartPoint="0.5,0" EndPoint="0.5,1">
        <GradientStop Color="Black" Offset="0"/>
        <GradientStop Color="#FF949494" Offset="1"/>
    </LinearGradientBrush>


    <LinearGradientBrush x:Key="GradPressd" StartPoint="0.5,0" EndPoint="0.5,1">
        <GradientStop Color="#FF666868" Offset="0"/>
        <GradientStop Color="Black" Offset="1"/>
    </LinearGradientBrush>


    <LinearGradientBrush x:Key="GradFocuse" StartPoint="0.5,0" EndPoint="0.5,1">
        <GradientStop Color="White" Offset="0"/>
        <GradientStop  Color="#FF5F5F5F" Offset="1"/>
    </LinearGradientBrush>

    <Style x:Key="SelectionButton3"
    TargetType="{x:Type Button}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Button}">

                    <Grid Name="grd" HorizontalAlignment="Stretch"
                    VerticalAlignment="Stretch"
                    ClipToBounds="False">
                        <Border x:Name="TheBorder" CornerRadius="10"  
                        Background="{StaticResource GradDefulat}"   Height="{Binding Path=Height}" Width="{Binding Path=Width}"
                        BorderBrush="DarkSlateBlue"> </Border>
                        <Rectangle Name="rect" Fill="{StaticResource GradDefulat}"  Stroke="DarkSlateBlue"
                         Height="200" Width="50"> 
                            <Rectangle.RenderTransform >
                                <RotateTransform Angle="45" CenterX=" 30" CenterY="25" >  
                                </RotateTransform>
                            </Rectangle.RenderTransform>
                        </Rectangle>
                        <ContentPresenter x:Name="ContentArea" VerticalAlignment="Center"   HorizontalAlignment="Center "
                                    Content="{Binding Path=Content, RelativeSource={RelativeSource TemplatedParent}}" />
                    </Grid>
                    <ControlTemplate.Triggers >

                        <Trigger Property="IsDefaulted" Value="True">
                            <Setter TargetName="TheBorder" Property ="Background" Value="{StaticResource GradDefulat}"/>
                            <Setter TargetName="TheBorder" Property="BorderBrush" Value="{StaticResource DefulateBorder}"/>
                            <Setter TargetName="rect" Property ="Fill" Value="{StaticResource GradDefulat}"/>
                            <Setter TargetName="rect" Property="Stroke" Value="{StaticResource DefulateBorder}"/>

                        </Trigger>
                        <!-- Defaulated-->

                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter TargetName="TheBorder" Property="Background" Value="{StaticResource GradOver}"/>
                            <Setter TargetName="TheBorder" Property="BorderBrush" Value="{StaticResource OverBorder}"/>
                            <Setter TargetName="rect" Property="Fill" Value="{StaticResource GradOver}"/>
                            <Setter TargetName="rect" Property="Stroke" Value="{StaticResource OverBorder}"/>
                        </Trigger>
                        <!-- Over-->

                        <Trigger Property="IsFocused" Value="True">
                            <Setter TargetName="TheBorder" Property="Background" Value="{StaticResource GradFocuse}"/>
                            <Setter TargetName="TheBorder" Property="BorderBrush" Value="{StaticResource FocuseBorder}"/>
                            <Setter TargetName="rect" Property="Fill" Value="{StaticResource GradFocuse}"/>
                            <Setter TargetName="rect" Property="Stroke" Value="{StaticResource FocuseBorder}"/>
                        </Trigger>
                        <!--Focuse-->

                        <Trigger Property="IsPressed" Value="True">
                            <Setter TargetName="TheBorder" Property="Background" Value="{StaticResource GradPressd}"/>
                            <Setter TargetName="TheBorder" Property="BorderBrush" Value="{StaticResource PressdBorder}"/>
                            <Setter TargetName="rect" Property="Fill" Value="{StaticResource GradPressd}"/>
                            <Setter TargetName="rect" Property="Stroke" Value="{StaticResource PressdBorder}"/>
                        </Trigger>
                        <!-- Focuse-->
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</Window.Resources> 

英语不是我的第一语言，所以我为缺乏细节而道歉。