ArcGIS Runtime SDK for iOS 100.3.0，如何能在界面显示比例尺

esri提供了一些可供直接使用的ui控件。链接：https://github.com/Esri/arcgis-runtime-toolkit-ios 
其中就包括比例尺。
如下：
Toolkit Components

Augmented reality (AR) - Integrates the scene view with ARKit to enable augmented reality (AR).
Bookmarks - Shows bookmarks, from a map, scene, or a list.
Compass - Shows a compass direction when the map is rotated. Auto-hides when the map points north up.
JobManager - Suspends and resumes ArcGIS Runtime tasks when the app is background, terminated, and relaunched.
LegendViewController - Displays a legend for all the layers in a map or scene contained in an AGSGeoView.
MeasureToolbar - Allows measurement of distances and areas on the map view.
PopupController - Display details and media, edit attributes, geometry and related records, and manage the attachments of features and graphics (popups are defined in the popup property of features and graphics).
Scalebar - Displays current scale reference.
TemplatePickerViewController - Allows a user to choose a template from a list of AGSFeatureTemplate when creating new features.
TimeSlider - Allows interactively defining a temporal range (i.e. time extent) and animating time moving forward or backward. Can be used to manipulate the time extent in a MapView or SceneView.