Learn how to automatically scroll an option into view when opening the autocomplete feature in an Angular 8. This functionality is particularly

I am currently working on implementing a feature that requires a field with functionality similar to a select input, but also allows the user to type in their own value if it's not available in the options. The key requirement is that the user should be able to either select from predefined options or input a valid value manually. The options should not be filtered based on input, but rather focus on finding a matching value within the available choices. I've been attempting to achieve this using mat autocomplete, however, I'm facing an issue with scrolling. How can I ensure that the selected option scrolls into view when typing in the field or refocusing on it after making a selection?

HTML

<div>
  <mat-form-field [appearance]="'outline'">
    <mat-label>Select color</mat-label>
    <input type="text" matInput [(ngModel)]="color" [matAutocomplete]="colorOptions">
    <i class="icon-caret-down select-arrow" matSuffix></i>
    <mat-hint>Select or type a color</mat-hint>
  </mat-form-field>
  <mat-autocomplete #colorOptions="matAutocomplete">
    <mat-option *ngFor="let option of colors; let i=index" [value]="option"
      [ngClass]="{'active-option': option == color}">
      {{option}}
    </mat-option>
  </mat-autocomplete>
</div>

TS

public colors = ['Red', 'Green', 'Blue', 'Yellow', 'Orange', 'White', 'Black', 'Purple', 'Grey', 'Brown'];
public color = '';

SCSS

.active-option {
  background-color: #f5f5f5 !important;
  font-weight: bold !important;
}

https://stackblitz.com/edit/angular-ivy-vetnpq

Answer №1

Alright, let's dive in...

First things first, check out this neat little StackBlitz demo.

Keep in mind that focusing on the selected element when using keydown from the input is not implemented here since it goes beyond the scope of the question. Generally, sticking to the default behavior would be my suggestion, but hey, you asked for it...

The CSS Part

In the HTML, there's a div marked with role='listbox'. Inside this div, you'll find the mat-option elements. When these elements overflow the container, a scrollbar with overflow: auto is added by the div. To scroll, we simply adjust the scrollTop value on the div.

Finding the Element

You can access the div through the autocomplete object via its property called panel. To do this, get the autocomplete object and reference it using @ViewChild().

Determining the ScrollTop Value

To determine the value, consider the height of the mat-option which defaults to 48. You should be able to retrieve this height from AUTOCOMPLETE_OPTION_HEIGHT.

Note: Modifying this value didn't yield visible results for me. It's possible I made an error or there might be other factors nullifying this constant change. Therefore, I've set it back to the default of 48.

To accurately compute the scrollTop value, calculate based on the index of the matched element.

Implementing the Logic via a Method Call

Invoke this logic through a method detecting value changes in the input field: (input)='changed_input().

My Code Snippets Below

app.module.ts

[... App Module code snippets ...]

app.component.html

[... App Component HTML code snippets ...]

app.component.ts

[... App Component TypeScript code snippets ...]

A Final Word

This experimentation is all well and good, but seriously, stick to the default behavior and spare yourself some future headaches.

Answer №2

If I grasp your intention correctly, you want to incorporate the user's input as an option in the mat-autocomplete selection. To achieve this, you can refer to the modified version of your code on StackBlitz via this edited-stackblitz.

In the updated code, I have introduced a button that, when pressed by the user, adds the entered option to the autocomplete list. Additionally, I have implemented functionality where pressing "enter" triggers the same action as the button click.

Here is the revised code snippet:
HTML:

<div [formGroup]="testForm">
  <mat-form-field [appearance]="'outline'">
    <mat-label>Select color</mat-label>
    <input type="text" matInput formControlName="color" 
          [matAutocomplete]="colorOptions" [(ngModel)]="currentOption">
    <i class="icon-caret-down select-arrow" matSuffix></i>
    <mat-hint>Select or type a color</mat-hint>
  </mat-form-field>
  <mat-autocomplete #colorOptions="matAutocomplete">
    <mat-option *ngFor="let option of colors; let i=index" [value]="option"
      [ngClass]="{'active-option': option == testForm.controls.color.value}">
      {{option}}
    </mat-option>
  </mat-autocomplete>
  <button (click)="addOption()">+</button>
  {{currentOption}}
 </div>

TS:

name = 'Angular ' + VERSION.major;
color = '';
colors = ['Red', 'Green', 'Blue', 'Yellow', 'Orange', 'White', 'Black', 'Purple', 'Grey', 'Brown'];
testForm: FormGroup;

ngOnInit(){
 this.testForm = new FormGroup({
   color: new FormControl('')
 })
}

public currentOption: any;

public addOption(): void {
 this.colors.push(this.currentOption);
}

Please confirm if my understanding aligns with your requirements.

Answer №3

To ensure that the panel scroll aligns with the selected and activated items, utilize the optionActivated and opened events on the mat-autocomplete component:

<mat-autocomplete 
(opened)="onPanelOpened()"
(optionActivated)="onOptionActivated($event)">

</mat-autocomplete>

In your component.ts file, create the onOptionActivated method for keydown and keyup focusing on the activated element and the onPanelOpened method to focus on the first selected item when the panel opens:

@ViewChild(MatAutocomplete) autoComplete!: MatAutocomplete;

onPanelOpened() {
   const firstSelectedOption = this.autoComplete.options.find(o => o.selected);

   firstSelectedOption?._getHostElement()?.scrollIntoView({
     block: 'center',
   });
}

onOptionActivated(event: MatAutocompleteActivatedEvent) {
   event.option?._getHostElement()?.scrollIntoView({
    block: 'end',
  });
}

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