NativeScript/apps/ui/app/tab-view/tab-view-icon-page.ts

import { EventData } from '@nativescript/core/data/observable';
import { Button } from '@nativescript/core/ui/button';
import { TabView } from '@nativescript/core/ui/tab-view';

let iconModes = ['automatic', 'alwaysOriginal', 'alwaysTemplate', undefined];

export const onNavigate = updateButtons;

export function onChangeRenderingMode(args: EventData) {
	let tabView = (<Button>args.object).page.getViewById<TabView>('tab-view');
	tabView.iosIconRenderingMode = <'automatic' | 'alwaysOriginal' | 'alwaysTemplate'>iconModes[(iconModes.indexOf(tabView.iosIconRenderingMode) + 1) % iconModes.length];
	updateButtons(args);
}

function updateButtons(args) {
	let button = <Button>args.object;
	let tabView = button.page.getViewById<TabView>('tab-view');
	for (let i = 0, length = tabView.items.length; i < length; i++) {
		(<Button>tabView.items[i].view).text = '' + tabView.iosIconRenderingMode;
	}
}