Information will only be displayed after the button has been double-clicked

Question

Information will only be displayed after the button has been double-clicked

After a month of experimenting with Angular and being relatively new to web development, I've encountered an issue that I hope someone can help me with. In my simple Angular application, I have a button called roomSearch() which sends form data to an MVC Web API. The data retrieved from the API is then displayed on the HTML page by the Angular component.

The problem is that I always have to click the button twice in order to see the result. It never works on the first click, and I'm struggling to understand why.

Here is the code snippet:

HTML Section:

<form #roomForm="ngForm" class="coupon-form" (ngSubmit)="onSubmit(roomForm)">
  <div class="row">
    ...
  </div>

  <div class="form-group">
    <button type="button" (click)="roomSearch(roomForm)" class="btn btn-lg btn-block btn-info"><i class="fa fa-floppy-o" aria-hidden="true"></i> Submit</button>
  </div>
</form>

...

Component File:

 show: boolean;

 ngOnInit() {
    this.show = this.roomService.show;
  }

  roomSearch(form: NgForm)
  {
    this.show = this.roomService.getRoomList(form.value.startDate, form.value.endDate);
  }

Service File:

 constructor(private http: Http) {
      this.show=false;
    } 

getRoomList(startDate: string, endDate:string){
    ...

The issue arises when I try to log the this.roomList on the console. It initially shows as undefined on the first click but displays the correct value on the second click. Can anyone point out what I might be doing wrong here?

angular typescript

Answer 1

Answer №1

Great job on organizing your code! It was really easy to follow.

The issue you're encountering is related to asynchronous behavior.

Angular utilizes Observables when making HTTP calls, which means the result of the call will come later, not immediately after the request is made.

In your specific case, here's what's happening:

this.http.get(this.finalUrl)
.map((data: Response)=>{
  return data.json() as Room[];
}).toPromise().then(x =>{
  this.roomList = x;
});

console.log(this.roomList);

You are logging `undefined` because you're not waiting for the promise to be resolved, meaning you're trying to access `this.roomList` before it has been assigned a value.

To fix this issue, consider the following approach:

processRequest(roomList: Room[]) {
  // Your processing logic goes here
}

// Remove everything after this line in your existing code

return this.http.get(this.finalUrl)
  .map((data: Response) => {
    return data.json() as Room[];
  }).toPromise().then(x => {
    return Promise.resolve(this.processRequest(x))
  });

Lastly, in your component, make sure to update the method to:

roomSearch(form: NgForm)
{
  this.roomService.getRoomList(form.value.startDate, form.value.endDate).then(show => this.show = show);
}

In summary, fetch the rooms via HTTP request, wait for the response, process the data using `processRequest`, and then bind the processed result to the appropriate variable in your component.

If you need further clarification, don't hesitate to ask!

Answer 2

Great job on organizing your code! It was really easy to follow.

The issue you're encountering is related to asynchronous behavior.

Angular utilizes Observables when making HTTP calls, which means the result of the call will come later, not immediately after the request is made.

In your specific case, here's what's happening:

this.http.get(this.finalUrl)
.map((data: Response)=>{
  return data.json() as Room[];
}).toPromise().then(x =>{
  this.roomList = x;
});

console.log(this.roomList);

You are logging `undefined` because you're not waiting for the promise to be resolved, meaning you're trying to access `this.roomList` before it has been assigned a value.

To fix this issue, consider the following approach:

processRequest(roomList: Room[]) {
  // Your processing logic goes here
}

// Remove everything after this line in your existing code

return this.http.get(this.finalUrl)
  .map((data: Response) => {
    return data.json() as Room[];
  }).toPromise().then(x => {
    return Promise.resolve(this.processRequest(x))
  });

Lastly, in your component, make sure to update the method to:

roomSearch(form: NgForm)
{
  this.roomService.getRoomList(form.value.startDate, form.value.endDate).then(show => this.show = show);
}

In summary, fetch the rooms via HTTP request, wait for the response, process the data using `processRequest`, and then bind the processed result to the appropriate variable in your component.

If you need further clarification, don't hesitate to ask!

Information will only be displayed after the button has been double-clicked

Answer №1

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