c#-如何访问MediaTransportControl中的自定义按钮引发的事件？

我有一个UWP桌面应用程序，它有一个带有自定义MediaTransportControl的MediaPlayerElement。我在MediaTransportControls中创建了两个新按钮，以增加和减少MediaPlayerElement的播放速率。我已经创建了在单击按钮时引发事件的过程，但我不知道如何访问应用程序主页上的这些事件，其中包含MediaPlayerElement。我该怎么做？欢迎任何帮助。

XAML

<MediaPlayerElement x:Name="mediaPlayerElement"

                                AutoPlay="False" 
                                HorizontalAlignment="Center" VerticalAlignment="Top"
                                Margin="0,0,0,100"
                                AreTransportControlsEnabled="True" >
                        <MediaPlayerElement.TransportControls>
                            <local:CustomMediaTransportControls x:Name="customMTC"
                                             IsSkipBackwardEnabled="False"
                                             IsSkipBackwardButtonVisible="False"
                                             IsSkipForwardEnabled="False"
                                             IsSkipForwardButtonVisible="False"
                                             IsFastForwardButtonVisible="True"
                                             IsFastForwardEnabled="True"
                                             IsFastRewindButtonVisible="True"
                                             IsFastRewindEnabled="True" 
                                            IsFullWindowButtonVisible="False"
                                            IsNextTrackButtonVisible="False"
                                            IsPreviousTrackButtonVisible="False"
                                            IsZoomButtonVisible="False"/>
                        </MediaPlayerElement.TransportControls>
                    </MediaPlayerElement>

<!--Custom Buttons-->
                                        <AppBarButton x:Name='CustomPlaybackRateDownButton'
                      Style='{StaticResource AppBarButtonStyle}'
                      MediaTransportControlsHelper.DropoutOrder='18' Visibility="Visible">
                                            <AppBarButton.Icon>
                                                <FontIcon FontFamily="Segoe MDL2 Assets" Glyph="&#xE70D;"/>
                                            </AppBarButton.Icon>
                                        </AppBarButton>

                                        <AppBarButton x:Name='CustomPlaybackRateUpButton'
                      Style='{StaticResource AppBarButtonStyle}'
                      MediaTransportControlsHelper.DropoutOrder='19' Visibility="Visible">
                                            <AppBarButton.Icon>
                                                <FontIcon FontFamily="Segoe MDL2 Assets" Glyph="&#xE70E;"/>
                                            </AppBarButton.Icon>
                                        </AppBarButton>

代码隐藏

public sealed class CustomMediaTransportControls : MediaTransportControls
{
    public event EventHandler PlaybackRateDownClicked;
    public event EventHandler PlaybackRateUpClicked;

    public CustomMediaTransportControls()
    {
        this.DefaultStyleKey = typeof(CustomMediaTransportControls);
    }


    protected override void OnApplyTemplate()
    {
        // Find the custom button and create an event handler for its Click event.
        var downButton = GetTemplateChild("CustomPlaybackRateDownButton") as Button;
        downButton.Click += CustomPlaybackRateDownButton_Click;

        var upButton = GetTemplateChild("CustomPlaybackRateUpButton") as Button;
        upButton.Click += CustomPlaybackRateUpButton_Click;

        base.OnApplyTemplate();
    }


    private void CustomPlaybackRateDownButton_Click(object sender, RoutedEventArgs e)
    {
        var OnPlaybackRateDownClick = PlaybackRateDownClicked;

        if (OnPlaybackRateDownClick != null)
        {
            OnPlaybackRateDownClick(this, EventArgs.Empty);
        }
    }

    private void CustomPlaybackRateUpButton_Click(object sender, RoutedEventArgs e)
    {
        var OnPlaybackRateUpClick = PlaybackRateUpClicked;

        if (OnPlaybackRateUpClick != null)
        {
            OnPlaybackRateUpClick(this, EventArgs.Empty);
        }
    }


}