UWP - Change Button VisualState dynamically

I am trying to change the button Pressed background dynamically. But I am unable to access to this property from the code behind. According to the base style of button, I tried to get the ControlTemplate (by the TemplateProperty) but there is no method from it to retrieve the Grid (RootGrid) it contains. So I tried to get VisualStateGroup like this:

var visualStateGroups = VisualStateManager.GetVisualStateGroups(testButton);

But this returns null.

Thanks for any help.

Samuel

To retrieve the Grid contained in the Button, you can use the method:

    private TChild FindVisualChild<TChild>(DependencyObject obj)where TChild : DependencyObject
    {
        for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
        {
            DependencyObject child = VisualTreeHelper.GetChild(obj, i);
            if (child != null && child is TChild)
                return (TChild)child;
            else
            {
                TChild childOfChild = FindVisualChild<TChild>(child);
                if (childOfChild != null)
                    return childOfChild;
            }
        }
        return null;
    }

Then use the method like this:

var grid = FindVisualChild<Grid>(this.test);
var group = VisualStateManager.GetVisualStateGroups(grid)[0];