How do I programmatically set focus to dynamically

问题:

I don't seem to be able to set focus on a input field in dynamically added FormGroup:

addNewRow(){
    (<FormArray>this.modalForm.get('group1')).push(this.makeNewRow());
    // here I would like to set a focus to the first input field
    // say, it is named 'textField'

    // but <FormControl> nor [<AbstractControl>][1] dont seem to provide 
    // either a method to set focus or to access the native element
    // to act upon
}

How do I set focus to angular2 FormControl or AbstractControl?

回答1:

I made this post back in December 2016, Angular has progressed significantly since then, so I'd make sure from other sources that this is still a legitimate way of doing things

---

You cannot set to a FormControl or AbstractControl, since they aren't DOM elements. What you'd need to do is have an element reference to them, somehow, and call .focus() on that. You can achieve this through ViewChildren (of which the API docs are non-existent currently, 2016-12-16).

In your component class:

import { ElementRef, ViewChildren } from '@angular/core';

// ...imports and such

class MyComponent {
    // other variables
    @ViewChildren('formRow') rows: ElementRef;

    // ...other code
    addNewRow() {
        // other stuff for adding a row
        this.rows.first().nativeElement.focus();
    }
}

If you wanted to focus on the last child...this.rows.last().nativeElement.focus()

And in your template something like:

<div #formRow *ngFor="let row in rows">
    <!-- form row stuff -->
</div>

EDIT:

I actually found a CodePen of someone doing what you're looking for https://codepen.io/souldreamer/pen/QydMNG

回答2:

For Angular 5, combining all of the above answers as follows:

Component relevant code:

 import { AfterViewInit, QueryList, ViewChildren, OnDestroy } from '@angular/core';
 import { Subscription } from 'rxjs/Subscription';

 // .. other imports

 export class MyComp implements AfterViewInit, OnDestroy {
   @ViewChildren('input') rows: QueryList<any>;
   private sub1:Subscription = new Subscription();
   //other variables ..

 // changes to rows only happen after this lifecycle event so you need
 // to subscribe to the changes made in rows.  
 // This subscription is to avoid memory leaks
 ngAfterViewInit() {
   this.sub1 = this.rows.changes.subscribe(resp => {
     if (this.rows.length > 1){
       this.rows.last.nativeElement.focus();
     }
   });
  }

  //memory leak avoidance
  ngOnDestroy(){
    this.sub1.unsubscribe();
  }


   //add a new input to the page
   addInput() {
     const formArray = this.form.get('inputs') as FormArray;

     formArray.push(
        new FormGroup(
        {input: new FormControl(null, [Validators.required])}
     ));
    return true;
   }

 // need for dynamic adds of elements to re 
 //focus may not be needed by others
 trackByFn(index:any, item:any){
    return index;
 }

The Template logic Looks like this:

 <div formArrayName="inputs" class="col-md-6 col-12" 
     *ngFor="let inputCtrl of form.get('phones').controls; 
             let i=index; trackBy:trackByFn">
     <div [formGroupName]="i">
        <input #input type="text" class="phone" 
             (blur)="addRecord()"
             formControlName="input" />
     </div>
 </div>

In my template I add a record on blur, but you can just as easily set up a button to dynamically add the next input field. The important part is that with this code, the new element gets the focus as desired.

Let me know what you think

回答3:

This is the safe method recommend by angular

@Component({
  selector: 'my-comp',
  template: `
    <input #myInput type="text" />
    <div> Some other content </div>
  `
})
export class MyComp implements AfterViewInit {
  @ViewChild('myInput') input: ElementRef;

  constructor(private renderer: Renderer) {}

  ngAfterViewInit() {
    this.renderer.invokeElementMethod(this.input.nativeElement,    
    'focus');
  }
}