如何使用JointJS获取UML类的elementView大小？

<script src="joint.min.js"></script>

var graph = new joint.dia.Graph();
var paper = new joint.dia.Paper({
  el: document.getElementById('paper'),
  model: graph,
  width: 800,
  height: 600,
});

var umlClass = new joint.shapes.uml.Class({
  position: { x: 100, y: 100 },
  size: { width: 200, height: 100 },
  name: 'MyClass',
  attributes: ['attr1: type', 'attr2: type'],
  methods: ['method1()', 'method2()'],
});

graph.addCell(umlClass);

var elementView = umlClass.findView(paper);
var elementSize = elementView.getBBox();
console.log('Width: ' + elementSize.width);
console.log('Height: ' + elementSize.height);