c# Toggle ribbon button

I am converting my ribbon from visual designer to XML and I am not sure how to change the state of the ribbon toggle button from other parts of the project. Previously, when I close my task pane via the close button on the task pane:

    private void btnClose_Click(object sender, EventArgs e)
    {
        Globals.ThisWorkbook.Application.DisplayDocumentActionTaskPane = false;
        Globals.Ribbons.Ribbon.btnTaskPane.Checked = false; 
    }

Now, that the code is in XML and the callback is:

    public bool btnTaskPaneToggled(Office.IRibbonControl control)
    {
        if (Globals.ThisWorkbook.Application.CommandBars["Task Pane"].Visible)
            return true;
        else
            return false;
    }

XML for toggle button:

                <toggleButton id="btnTaskPane" 
                              onAction="btnTaskPane_Click" 
                              getPressed="btnTaskPaneToggled"
                              screentip="Task Pane" 
                              supertip="Toggle Task Pane on and off." 
                              label="&amp;Task Pane" 
                              size="large" 
                              getImage="GetIcon" />

How do I call the Ribbon callback from the close button?