NativeScript/tns-core-modules/ui/activity-indicator/activity-indicator-common.ts

import { ActivityIndicator as ActivityIndicatorDefinition } from "ui/activity-indicator";
import { View } from "ui/core/view";
import { Property } from "ui/core/properties";

export class ActivityIndicatorBase extends View implements ActivityIndicatorDefinition {
    public busy: boolean;
}

export let busyProperty = new Property<ActivityIndicatorBase, boolean>({ name: "busy", defaultValue: false });
busyProperty.register(ActivityIndicatorBase);