Use the resulting value to update your marker (Label, HtmlDrawable or whatever you're using for visualization)
Listen on context.onLocationChanged and run the distance calculation function in point 1 whenever the user changes location to update the distance.
The samples application in our examples uses a very similar approach, but updates the HTML content. Just follow along with this example, and instead of updating the HTML, update the text in your markers.
Sutiwat Khamhaeng
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