此组件显示一个动画“加载中”控件，告知用户操作正在进行中。只要组件显示，动画就会持续。
// Color of indicator
color: color;
// Number of ms to wait before displaying
deferTime: number = 0;
// Size of indicator (exact sizes are platform-specific)
size: 'large' | 'medium' | 'small' | 'tiny';
// ID that can be used to identify the instantiated element for testing purposes.
testId: string = undefined;
无方法