tabs-page.ts

import { EventData } from "tns-core-modules/data/observable";
import { Page } from "tns-core-modules/ui/page";
import { Tabs } from "tns-core-modules/ui/tabs";

export function goToFirst(args: EventData) {
  console.log("---> goToFirst");
  const page = <Page>(<any>args.object).page;
  const tabsNav = <Tabs>page.getViewById("tabsNav");

  tabsNav.selectedIndex = 0;
}

export function goToSecond(args: EventData) {
  console.log("---> goToSecond");
  const page = <Page>(<any>args.object).page;
  const tabsNav = <Tabs>page.getViewById("tabsNav");

  tabsNav.selectedIndex = 1;
}

export function goToThird(args: EventData) {
  console.log("---> goToThird");
  const page = <Page>(<any>args.object).page;
  const tabsNav = <Tabs>page.getViewById("tabsNav");

  tabsNav.selectedIndex = 2;
}

export function onFirstTabStripItemTap(args: EventData) {
  console.log("---> onFirstTabStripItemTap");
  console.log("---> args.object", args.object);
}

export function onSecondTabStripItemTap(args: EventData) {
  console.log("---> onSecondTabStripItemTap");
  console.log("---> args.object", args.object);
}

export function onThirdTabStripItemTap(args: EventData) {
  console.log("---> onThirdTabStripItemTap");
  console.log("---> args.object", args.object);
}

tabs-page.xml

<Page>

  <Tabs id="tabsNav">

    <TabStrip>
      <TabStripItem title="First" tap="onFirstTabStripItemTap"></TabStripItem>
      <TabStripItem tap="onSecondTabStripItemTap">
        <Label text="Second" />
      </TabStripItem>
      <TabStripItem title="First" tap="onThirdTabStripItemTap">
        <Label text="Third" />
      </TabStripItem>
    </TabStrip>

    <TabContentItem>
      <StackLayout>
        <Label text="First View" backgroundColor="red" />
        <Button tap="goToSecond" text="go to second" />
      </StackLayout>
    </TabContentItem>
    <TabContentItem>
      <StackLayout>
        <Label text="Second View" backgroundColor="green" />
        <Button tap="goToThird" text="go to thrid" />
      </StackLayout>
    </TabContentItem>
    <TabContentItem>
      <StackLayout>
        <Label text="First View" backgroundColor="blue" />
        <Button tap="goToFirst" text="go to first" />
      </StackLayout>
    </TabContentItem>

  </Tabs>

</Page>