feat(material/autocomplete): add input to require selection from the panel

Adds the `requireSelection` input to the autocomplete, which when enabled will clear the input value if the user doesn't select an option from the list.

Fixes #3334.

Author: crisbeto

src/components-examples/material/autocomplete/autocomplete-require-selection/autocomplete-require-selection-example.css

@@ -0,0 +1,9 @@
+.example-form {
+  min-width: 150px;
+  max-width: 500px;
+  width: 100%;
+}
+
+.example-full-width {
+  width: 100%;
+}

src/components-examples/material/autocomplete/autocomplete-require-selection/autocomplete-require-selection-example.html

@@ -0,0 +1,18 @@
+<form class="example-form">
+  <mat-form-field class="example-full-width">
+    <mat-label>Number</mat-label>
+    <input type="text"
+           placeholder="Pick one"
+           aria-label="Number"
+           matInput
+           [formControl]="myControl"
+           [matAutocomplete]="auto">
+    <mat-autocomplete requireSelection #auto="matAutocomplete">
+      <mat-option *ngFor="let option of filteredOptions | async" [value]="option">
+        {{option}}
+      </mat-option>
+    </mat-autocomplete>
+  </mat-form-field>
+</form>
+
+Control value: {{myControl.value}}

src/components-examples/material/autocomplete/autocomplete-require-selection/autocomplete-require-selection-example.ts

@@ -0,0 +1,45 @@
+import {Component, OnInit} from '@angular/core';
+import {FormControl, FormsModule, ReactiveFormsModule} from '@angular/forms';
+import {Observable} from 'rxjs';
+import {map, startWith} from 'rxjs/operators';
+import {NgFor, AsyncPipe} from '@angular/common';
+import {MatAutocompleteModule} from '@angular/material/autocomplete';
+import {MatInputModule} from '@angular/material/input';
+import {MatFormFieldModule} from '@angular/material/form-field';
+
+/**
+ * @title Require an autocomplete option to be selected.
+ */
+@Component({
+  selector: 'autocomplete-require-selection-example',
+  templateUrl: 'autocomplete-require-selection-example.html',
+  styleUrls: ['autocomplete-require-selection-example.css'],
+  standalone: true,
+  imports: [
+    FormsModule,
+    MatFormFieldModule,
+    MatInputModule,
+    MatAutocompleteModule,
+    ReactiveFormsModule,
+    NgFor,
+    AsyncPipe,
+  ],
+})
+export class AutocompleteRequireSelectionExample implements OnInit {
+  myControl = new FormControl('');
+  options: string[] = ['One', 'Two', 'Three', 'Three', 'Four'];
+  filteredOptions: Observable<string[]>;
+
+  ngOnInit() {
+    this.filteredOptions = this.myControl.valueChanges.pipe(
+      startWith(''),
+      map(value => this._filter(value || '')),
+    );
+  }
+
+  private _filter(value: string): string[] {
+    const filterValue = value.toLowerCase();
+
+    return this.options.filter(option => option.toLowerCase().includes(filterValue));
+  }
+}

src/components-examples/material/autocomplete/index.ts

@@ -5,4 +5,5 @@ export {AutocompleteOptgroupExample} from './autocomplete-optgroup/autocomplete-
 export {AutocompleteOverviewExample} from './autocomplete-overview/autocomplete-overview-example';
 export {AutocompletePlainInputExample} from './autocomplete-plain-input/autocomplete-plain-input-example';
 export {AutocompleteSimpleExample} from './autocomplete-simple/autocomplete-simple-example';
+export {AutocompleteRequireSelectionExample} from './autocomplete-require-selection/autocomplete-require-selection-example';
 export {AutocompleteHarnessExample} from './autocomplete-harness/autocomplete-harness-example';

src/dev-app/autocomplete/autocomplete-demo.html

@@ -10,9 +10,11 @@
       <mat-label>State</mat-label>
       <input matInput [matAutocomplete]="reactiveAuto" [formControl]="stateCtrl">
     </mat-form-field>
-    <mat-autocomplete #reactiveAuto="matAutocomplete" [displayWith]="displayFn"
+    <mat-autocomplete #reactiveAuto="matAutocomplete"
+      [displayWith]="displayFn"
       [hideSingleSelectionIndicator]="reactiveHideSingleSelectionIndicator"
-      [autoActiveFirstOption]="reactiveAutoActiveFirstOption">
+      [autoActiveFirstOption]="reactiveAutoActiveFirstOption"
+      [requireSelection]="reactiveRequireSelection">
       <mat-option *ngFor="let state of tempStates; let index = index" [value]="state"
         [disabled]="reactiveIsStateDisabled(state.index)">
         <span>{{ state.name }}</span>
@@ -45,6 +47,11 @@
         Automatically activate first option
       </mat-checkbox>
     </p>
+    <p>
+      <mat-checkbox [(ngModel)]="reactiveRequireSelection">
+        Require Selection
+      </mat-checkbox>
+    </p>
 
   </mat-card>
 
@@ -60,7 +67,8 @@
         (ngModelChange)="tdStates = filterStates(currentState)" [disabled]="tdDisabled">
       <mat-autocomplete #tdAuto="matAutocomplete"
         [hideSingleSelectionIndicator]="templateHideSingleSelectionIndicator"
-        [autoActiveFirstOption]="templateAutoActiveFirstOption">
+        [autoActiveFirstOption]="templateAutoActiveFirstOption"
+        [requireSelection]="templateRequireSelection">
         <mat-option *ngFor="let state of tdStates" [value]="state.name"
           [disabled]="templateIsStateDisabled(state.index)">
           <span>{{ state.name }}</span>
@@ -89,6 +97,11 @@
         Automatically activate first option
       </mat-checkbox>
     </p>
+    <p>
+      <mat-checkbox [(ngModel)]="templateRequireSelection">
+        Require Selection
+      </mat-checkbox>
+    </p>
     <p>
       <label for="template-disable-state-options">Disable States</label>
       <select [(ngModel)]="templateDisableStateOption" id="template-disable-state-options">

src/dev-app/autocomplete/autocomplete-demo.ts

@@ -59,7 +59,6 @@ export class AutocompleteDemo {
   tdStates: State[];
 
   tdDisabled = false;
-  hideSingleSelectionIndicators = false;
   reactiveStatesTheme: ThemePalette = 'primary';
   templateStatesTheme: ThemePalette = 'primary';
 
@@ -69,6 +68,9 @@ export class AutocompleteDemo {
     {value: 'warn', name: 'Warn'},
   ];
 
+  reactiveRequireSelection = false;
+  templateRequireSelection = false;
+
   reactiveHideSingleSelectionIndicator = false;
   templateHideSingleSelectionIndicator = false;
 

src/material/autocomplete/autocomplete-trigger.ts

@@ -110,6 +110,9 @@ export abstract class _MatAutocompleteTriggerBase
   /** Old value of the native input. Used to work around issues with the `input` event on IE. */
   private _previousValue: string | number | null;
 
+  /** Value of the input element when the panel was opened. */
+  private _valueOnOpen: string | number | null;
+
   /** Strategy that is used to position the panel. */
   private _positionStrategy: FlexibleConnectedPositionStrategy;
 
@@ -561,7 +564,7 @@ export abstract class _MatAutocompleteTriggerBase
                 //   of the available options,
                 // - if a valid string is entered after an invalid one.
                 if (this.panelOpen) {
-                  this.autocomplete.opened.emit();
+                  this._finalizeOpen();
                 } else {
                   this.autocomplete.closed.emit();
                 }
@@ -578,6 +581,12 @@ export abstract class _MatAutocompleteTriggerBase
     );
   }
 
+  /** Finalized the opening sequence once it's known that the panel will be shown. */
+  private _finalizeOpen() {
+    this._valueOnOpen = this._element.nativeElement.value;
+    this.autocomplete.opened.emit();
+  }
+
   /** Destroys the autocomplete suggestion panel. */
   private _destroyPanel(): void {
     if (this._overlayRef) {
@@ -616,14 +625,28 @@ export abstract class _MatAutocompleteTriggerBase
    * stemmed from the user.
    */
   private _setValueAndClose(event: MatOptionSelectionChange | null): void {
+    const panel = this.autocomplete;
     const toSelect = event ? event.source : this._pendingAutoselectedOption;
 
     if (toSelect) {
       this._clearPreviousSelectedOption(toSelect);
       this._assignOptionValue(toSelect.value);
+      // TODO(crisbeto): this should wait until the animation is done, otherwise the value
+      // gets reset while the panel is still animating which looks glitchy. It'll likely break
+      // some tests to change it at this point.
       this._onChange(toSelect.value);
-      this.autocomplete._emitSelectEvent(toSelect);
+      panel._emitSelectEvent(toSelect);
       this._element.nativeElement.focus();
+    } else if (panel.requireSelection && this._element.nativeElement.value !== this._valueOnOpen) {
+      this._clearPreviousSelectedOption(null);
+      this._assignOptionValue(null);
+      // Wait for the animation to finish before clearing the form control value, otherwise
+      // the options might change while the animation is running which looks glitchy.
+      if (panel._animationDone) {
+        panel._animationDone.pipe(take(1)).subscribe(() => this._onChange(null));
+      } else {
+        this._onChange(null);
+      }
     }
 
     this.closePanel();
@@ -633,13 +656,13 @@ export abstract class _MatAutocompleteTriggerBase
    * Clear any previous selected option and emit a selection change event for this option
    */
   private _clearPreviousSelectedOption(skip: _MatOptionBase | null, emitEvent?: boolean) {
-    if (this.autocomplete && this.autocomplete.options) {
-      this.autocomplete.options.forEach(option => {
-        if (option !== skip && option.selected) {
-          option.deselect(emitEvent);
-        }
-      });
-    }
+    // Null checks are necessary here, because the autocomplete
+    // or its options may not have been assigned yet.
+    this.autocomplete?.options?.forEach(option => {
+      if (option !== skip && option.selected) {
+        option.deselect(emitEvent);
+      }
+    });
   }
 
   private _attachOverlay(): void {
@@ -683,7 +706,7 @@ export abstract class _MatAutocompleteTriggerBase
     // We need to do an extra `panelOpen` check in here, because the
     // autocomplete won't be shown if there are no options.
     if (this.panelOpen && wasOpen !== this.panelOpen) {
-      this.autocomplete.opened.emit();
+      this._finalizeOpen();
     }
   }
 

src/material/autocomplete/autocomplete.html

@@ -7,6 +7,7 @@
     [attr.aria-label]="ariaLabel || null"
     [attr.aria-labelledby]="_getPanelAriaLabelledby(formFieldId)"
     [@panelAnimation]="isOpen ? 'visible' : 'hidden'"
+    (@panelAnimation.done)="_animationDone.next($event)"
     #panel>
     <ng-content></ng-content>
   </div>

src/material/autocomplete/autocomplete.md

@@ -7,11 +7,11 @@ defined by a `mat-option` tag. Set each option's value property to whatever you'
 of the text input to be when that option is selected.
 
 <!-- example({"example":"autocomplete-simple",
-              "file":"autocomplete-simple-example.html", 
+              "file":"autocomplete-simple-example.html",
               "region":"mat-autocomplete"}) -->
 
-Next, create the input and set the `matAutocomplete` input to refer to the template reference we assigned 
-to the autocomplete. Let's assume you're using the `formControl` directive from `ReactiveFormsModule` to 
+Next, create the input and set the `matAutocomplete` input to refer to the template reference we assigned
+to the autocomplete. Let's assume you're using the `formControl` directive from `ReactiveFormsModule` to
 track the value of the input.
 
 > Note: It is possible to use template-driven forms instead, if you prefer. We use reactive forms
@@ -25,7 +25,7 @@ panel instance into a local template variable (here we called it "auto"), and bi
 to the input's `matAutocomplete` property.
 
 <!-- example({"example":"autocomplete-simple",
-              "file":"autocomplete-simple-example.html", 
+              "file":"autocomplete-simple-example.html",
               "region":"input"}) -->
 
 ### Adding a custom filter
@@ -61,6 +61,22 @@ desired display value. Then bind it to the autocomplete's `displayWith` property
 
 <!-- example(autocomplete-display) -->
 
+### Require an option to be selected
+
+By default, the autocomplete will accept the value that the user typed into the input field.
+Instead, if you want to instead ensure that an option from the autocomplete was selected, you can
+enable the `requireSelection` input on `mat-autocomplete`. This will change the behavior of
+the autocomplete in the following ways:
+1. If the user opens the autocomplete, changes its value, but doesn't select anything, the
+autocomplete value will be reset back to `null`.
+2. If the user opens and closes the autocomplete without changing the value, the old value will
+be preserved.
+
+This behavior can be configured globally using the `MAT_AUTOCOMPLETE_DEFAULT_OPTIONS`
+injection token.
+
+<!-- example(autocomplete-require-selection) -->
+
 ### Automatically highlighting the first option
 
 If your use case requires for the first autocomplete option to be highlighted when the user opens
@@ -112,7 +128,7 @@ autocomplete is attached to using the `matAutocompleteOrigin` directive together
 ### Option groups
 `mat-option` can be collected into groups using the `mat-optgroup` element:
 <!-- example({"example":"autocomplete-optgroup",
-              "file":"autocomplete-optgroup-example.html", 
+              "file":"autocomplete-optgroup-example.html",
               "region":"mat-autocomplete"}) -->
 
 ### Accessibility
@@ -132,4 +148,4 @@ navigation though the autocomplete options.
 
 By default, `MatAutocomplete` displays a checkmark to identify the selected item. While you can hide
 the checkmark indicator via `hideSingleSelectionIndicator`, this makes the component less accessible
-by making it harder or impossible for users to visually identify selected items.
+by making it harder or impossible for users to visually identify selected items.