<button (click)="Send()">送出</button><br>

import { Component, OnInit, Output } from '@angular/core';

import { EventEmitter } from '@angular/core';

@Component({

  selector: 'app-todo-input',

  templateUrl: './todo-input.component.html',

  styleUrls: ['./todo-input.component.css']

})

export class TodoInputComponent implements OnInit {

  public content: string;

  @Output() onSend: EventEmitter<string> = new EventEmitter<string>();

  constructor() { }

  ngOnInit(): void {

    this.content = "Hello";

  }

  Send(){

    this.onSend.emit(this.content);

  }

}

<app-todo-input (onSend)="onSend($event)"></app-todo-input>

import { Component, OnInit } from '@angular/core';

import {Todo} from '../../models/todo'

@Component({

  selector: 'app-todo',

  templateUrl: './todo.component.html',

  styleUrls: ['./todo.component.css']

})

export class TodoComponent implements OnInit {

  public List:Todo[]=[];

  constructor() { }

  ngOnInit(): void {

    // this.List = [

    //   {id:1,content:'Test'},

    //   {id:2,content:'Test2'},

    //   {id:3,content:'Test3'},

    // ];

  }

  onSend(content: string){

    alert(content);

  }

}