Angular 13 - 数据可在组件内部访问，但未显示在 html 页面上

Question

所以，我现在正在学习 Angular，并尝试做一个 CRUD 应用程序。几乎一切正常，除了尝试使用 ID 获取数据时，我可以访问 component.ts 文件中的所有数据，但同样不会呈现到 html 文件中。这是我尝试过的：-

edit-to.component.ts

export class EditTodoComponent implements OnInit {

private tid: number = 0;

  public Todo:TodoModel= null ;
  public desc:string='';
  public title:string='';
  public id:number;

  constructor(private route: ActivatedRoute, private http:HttpClient) { }

  ngOnInit(): void {
    this.route.paramMap.subscribe(all_params =>{
      this.tid = parseInt(all_params.get('id'))
      //console.log( all_params.get('id'))
      //console.log( this.tid );
    });

    this.getTodoFromId(this.tid)


  }

   getTodoFromId(id){
    //console.log("id="+id)
     this.http.get<{data: any}>('http://localhost:3000/api/todos/get_todo_from_id/'+id).subscribe((data) =>{
      console.log("response in angular= \n");
      this.Todo = data[0]
      

      console.log(this.Todo.todo_title) //-> This one works

}
editOnSubmit(form:NgForm){
  //something here
}

edit-todo.component.html

 <div class="col-md-12">
    <form (ngSubmit)="editOnSubmit(todoForm)" #todoForm="ngForm">
      <input type="text" class="form-control" id="todo_id" [(ngModel)]="id" name="todo_id" value="1">
      <div class="mb-3">
        <label for="todo_title" class="form-label">Title</label>

        <input type="text" class="form-control" id="todo_title" [(ngModel)]="title" name="title" value="{{ Todo.todo_title}}">  //-> This one does not work.

      </div>
      <div class="mb-3">
        <label for="label" class="form-label">Description</label>
        <textarea  class="form-control" id="todo_description" [(ngModel)]="desc" name="desc" ></textarea>
      </div>

      <button type="submit" class="btn btn-success">Edit To Do</button>
    </form>
  </div>
</div>

分离出来，

来自 edit-to.component.ts :-

console.log(this.Todo.todo_title) 有效

但来自 edit-todo.component.html

<input type="text" class="form-control" id="todo_title" [(ngModel)]="title" name="title" value="{{ Todo.todo_title}}"> 不起作用

Answer 1

定义一个 BehaviorSubject 类型的属性。

isAvailableData = new BehaviorSubject<boolean>(true);

然后你订阅数据的地方设置为true。

getTodoFromId(id){
//console.log("id="+id)
 this.http.get<{data: any}>('http://localhost:3000/api/todos/get_todo_from_id/'+id).subscribe((data) =>{
  console.log("response in angular= \n");
  this.Todo = data[0];

  this.isAvailableData.next(true);

  console.log(this.Todo.todo_title) //-> This one works

}

然后在你的 HTML 中添加 ngIf 到 col-md-12 div：

<div class="col-md-12" *ngIf="(isAvailableData | async)">
<form (ngSubmit)="editOnSubmit(todoForm)" #todoForm="ngForm">
  <input type="text" class="form-control" id="todo_id" [(ngModel)]="id" name="todo_id" value="1">
  <div class="mb-3">
    <label for="todo_title" class="form-label">Title</label>

    <input type="text" class="form-control" id="todo_title" [(ngModel)]="title" name="title" value="{{ Todo.todo_title}}">  //-> This one does not work.

  </div>
  <div class="mb-3">
    <label for="label" class="form-label">Description</label>
    <textarea  class="form-control" id="todo_description" [(ngModel)]="desc" name="desc" ></textarea>
  </div>

  <button type="submit" class="btn btn-success">Edit To Do</button>
</form>

另外，您在表单中犯了错误，输入应如下所示：

而且没有必要为 id、title、...定义一个属性 这些是 todo 对象的属性

 <label for="todo_title" class="form-label">Title</label>

  <input type="text" class="form-control" id="todo_title" [(ngModel)]="Todo.todo_title" name="todo_title" #todo_title="ngModel">

Answer 2

这是因为您在同一输入字段上配置了一个 ngModel 和一个值

在这种情况下，ngModel 优先于 value 属性

要修复它，您可以在 ngOnInit 中初始化标题

this.title = this.Todo.todo_title; 

在您的情况下，您等待来自 http 请求的回复，因此在 hte http 回复之后进行初始化：

getTodoFromId(id){
     this.http.get<{data: any}>('http://localhost:3000/api/todos/get_todo_from_id/'+id).subscribe((data) =>{
      console.log("response in angular= \n");
      this.Todo = data[0]
      this.title = this.Todo.todo_title;

      console.log(this.Todo.todo_title);

}