I managed to solve my problem, based on pskink's suggestion. Here is my class:
public class RoundedBackgroundSpan : ReplacementSpan
{
public override void Draw(Canvas canvas, ICharSequence text, int start, int end, float x, int top, int y, int bottom, Paint paint)
{
var rect = new RectF(x, top, x + MeasureText(paint, text, start, end), bottom);
paint.Color = Application.Context.Resources.GetColor(Resource.Color.nextTimeBackgroundColor);
canvas.DrawRoundRect(rect, Application.Context.Resources.GetDimensionPixelSize(Resource.Dimension.localRouteDetailsRoundRectValue), Application.Context.Resources.GetDimensionPixelSize(Resource.Dimension.localRouteDetailsRoundRectValue), paint);
paint.Color = Application.Context.Resources.GetColor(Resource.Color.nextTimeTextColor);
canvas.DrawText(text, start, end, x, y, paint);
}
public override int GetSize(Paint paint, ICharSequence text, int start, int end, Paint.FontMetricsInt fm)
{
return Math.Round(MeasureText(paint, text, start, end));
}
private float MeasureText(Paint paint, ICharSequence text, int start, int end)
{
return paint.MeasureText(text, start, end);
}
}
Example usage:
var stringBuilder = new SpannableStringBuilder();
var stringToAppend = "hello world";
stringBuilder.Append(stringToAppend);
stringBuilder.SetSpan(new RoundedBackgroundSpan(), stringBuilder.Length() - stringToAppend.Length, stringBuilder.Length(), SpanTypes.ExclusiveExclusive);