/// <inheritdoc/>
public NavigationRequest GoBack()
{
if (CurrentLayer.CanGoBack)
{
var req = CurrentLayer.GoBack();
requestStream.EmitValue(req);
return(req);
}
else if (layers.Count > 1 && CurrentLayer.IsReturnable)
{
layers.RemoveAt(layers.Count - 1);
var req = NavigationRequest.Close;
requestStream.EmitValue(req);
return(req);
}
else
{
throw new InvalidOperationException("The current state of the NavigationHistory does not support back navigation.");
}
}