Animate Image

Hi,
I am trying to change an image using a timer in my XAML constructor. It doesn't fail but the image doesn't change.

Device.StartTimer(TimeSpan.FromSeconds(1), () =>
 {
        RadarImage = greenRadar[grIndex++];
                if (grIndex >= 24)
                        grIndex = 0;
                return true;
});

I thought it might be because it is not on the main thread so I added :-

Device.StartTimer(TimeSpan.FromSeconds(1), () =>
 {
        Device.BeginInvokeOnMainThread(() =>
        {
                RadarImage = greenRadar[grIndex++];
        });
        if (grIndex >= 24)
                grIndex = 0;
        return true;
});

The image still does not change. I have another routine which scales images within a timer and that works fine. Any ideas ?
Also, I can't find any info or examples of the
RadarImage.Animate()
method of an imageview. Would it be better to use that and if so any examples on how ?

Cheers,
Wayne