/// <summary>
/// Looks first in externalGroups, then in localGroups for the type of PlotGroupStyle to apply.
/// In contrast to <see cref="GetStyleToApply{T}(IPlotGroupStyleCollection, IPlotGroupStyleCollection)"/>, we are searching here only for an interface,
/// and return the first plot group style found that implements that interface.
/// If an instance with this interface found, this instance is returned. If found, the containig collection
/// is informed that this group style will be applied now by calling OnBeforeApplication.
/// </summary>
/// <typeparam name="T">Type of the interface to look for.</typeparam>
/// <param name="externalGroups">First collection to look for the group style.</param>
/// <param name="localGroups">Second collection to look for the group style.</param>
/// <returns>The instance of the plot group style that implements the interface (if found), or null otherwise.</returns>
public static T GetFirstStyleToApplyImplementingInterface <T>(
IPlotGroupStyleCollection externalGroups,
IPlotGroupStyleCollection localGroups
)
{
IPlotGroupStyle grpStyle = null;
IPlotGroupStyleCollection grpColl = externalGroups;
grpStyle = grpColl.FirstOrDefault(style => typeof(T).IsAssignableFrom(style.GetType()));
if (null == grpStyle)
{
grpColl = localGroups;
grpStyle = grpColl.FirstOrDefault(style => typeof(T).IsAssignableFrom(style.GetType()));
}
if (null != grpStyle)
{
grpColl.OnBeforeApplication(grpStyle.GetType());
}
return((T)grpStyle);
}