Angular UI not updating after data changes - mean-stack

Question

Im new to the MEAN stack and having trouble with getting data changes to be refreshed in the UI. I know the data is getting saved properly in MongoDB, and also retrieved, because when I create a Todo item and I refresh the page, the newly added Todo item appears in the Todo List. The problem is that it isnt happening dynamically.
I've tried a number of different things including NgZone and ChangeDetectorRef to detect changes, not sure what I'm doing wrong..
Let me know if any more info is needed.. thank you!
The Todo List component:
import { Component, Input, OnInit, NgZone } from '#angular/core';
import { Todo } from '../todo.model';
import { TodoService } from '../../todo.service';
#Component({
selector: 'app-todo-list',
templateUrl: './todo-list.component.html',
styleUrls: ['./todo-list.component.scss'],
providers: [TodoService]
})
export class TodoListComponent implements OnInit {
#Input() todos: Todo[] = [];
constructor(private _todoService: TodoService, private zone: NgZone){}
getTodos() {
console.log('todo list - get todos');
this._todoService.getTodos()
.subscribe(resTodoData => {
this.zone.run(() => {
this.todos = resTodoData;
});
});
}
ngOnInit() {
console.log('todo list - init');
this.getTodos();
}
}
Service Component:
import { Injectable, NgZone } from '#angular/core';
import { Http, Response, Headers, RequestOptions } from
'#angular/http';
import { map } from 'rxjs/operators';
import { Todo } from './todos/todo.model';
#Injectable({
providedIn: 'root'
})
export class TodoService {
// these were configured in express server
private _getUrl = "/api/todos";
private _postUrl = "/api/todo";
constructor(private _http: Http, private zone: NgZone) { }
getTodos() {
let json = this._http.get(this._getUrl)
.pipe(map((response: Response) => response.json()));
return json;
}
addTodo(todo: Todo) {
let headers = new Headers({ 'Content-Type': 'application/json'
});
let options = new RequestOptions({ headers: headers });
return this._http.post(this._postUrl, JSON.stringify(todo),
options)
.pipe(map((response: Response) => response.json()));
}
}