PullDownToRefreshPanel1.cs

private void PullDownToRefreshPanel_LayoutUpdated(object sender, EventArgs e)
{
    if (this.targetScrollViewer == null)
    {
        this.targetScrollViewer = FindVisualElement<ScrollViewer>(VisualTreeHelper.GetParent(this));
        if (this.targetScrollViewer != null)
        {
            this.LayoutUpdated -= PullDownToRefreshPanel_LayoutUpdated;

            // *snip*
        }
    }
}

PullDownToRefreshPanel2.cs

//double doubleValue = -System.Convert.ToDouble(value);
double doubleValue = -(double)value; // No convert needed