Angular ViewChild fileInput annotation is undefined

问题

If my fileInput element is in a normal div, then it works fine. But if I place it inside <ng-template></ng-template> then I am getting it undefined.

Here is my code :

HTML

<ng-template #content let-c="close" let-d="dismiss">
   <div class="modal-header">
      <h4 class="modal-title">Modal title</h4>
      <button type="button" class="close" aria-label="Close" (click)="d('Cross click')"></button>
   </div>
   <div class="modal-body">
      <form #documentsForm="ngForm" (ngSubmit)="onEditSubscriberDocumentsSubmit(documentsForm.value);documentsForm.reset()">
         <input #fileInput type="file" #select name="document" [(ngModel)]="document" (click)="onDocUpload()" />       
         <input type="submit" value="Save" class="btn btn-success" [hidden]="addDocHidden">
      </form>
   </div>
   <div class="modal-footer">
      <button type="button" class="btn btn-outline-dark" (click)="c('Close click')">Close</button>
   </div>
</ng-template>

TS

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

export class EditSubscriberComponent {
    constructor(private http: Http, private route: ActivatedRoute, private router: Router, private modalService: NgbModal) { }
    @ViewChild("fileInput") fileInput: ElementRef;
    ngOnInit() {
       console.log(this.fileInput)
       // This is undefined. If I place the <input #fileInput type="file"> 
       // in the main div,not under ng-template, then I am getting the 
       // desired output
    }
}

Please suggest how can I access ViewChild from ng-template

回答1:

You can either use setter:

@ViewChild("fileInput") 
set fileInput(val: ElementRef) {
  if(val) {
    console.log(val);
  }
}

or subscribe on @ViewChildren changes:

@ViewChildren("fileInput") fileInputs: QueryList<ElementRef>;

ngAfterViewInit() {
  this.fileInputs.changes.subscribe(x => {
    if(x.length) {
      console.log(x[0]);
    }
  })
}

or if you know exactly when your template is initialized then just use @ViewChild

@ViewChild("fileInput") fileInput: ElementRef;

...
this.vcRef.createEmbeddedView(this.template); // pseudo code
console.log(this.fileInput);

来源：https://stackoverflow.com/questions/46251282/angular-viewchild-fileinput-annotation-is-undefined