src/material/form-field/form-field.ts - main - githubmirror/components

src/material/form-field/form-field.ts
830 строк33 KB
Lazizbek Ergashev
fix(material/form-field): update view when the control is swapped out (#33636)
05 авг 2026, 19:43
05 авг 2026, 19:43e9760b3
/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.dev/license
 */
import {_IdGenerator} from '@angular/cdk/a11y';
import {Direction, Directionality} from '@angular/cdk/bidi';
import {BooleanInput, coerceBooleanProperty} from '@angular/cdk/coercion';
import {Platform} from '@angular/cdk/platform';
import {NgTemplateOutlet} from '@angular/common';
import {
  AfterContentChecked,
  AfterContentInit,
  AfterViewInit,
  ChangeDetectorRef,
  Component,
  ContentChild,
  ContentChildren,
  ElementRef,
  InjectionToken,
  Input,
  NgZone,
  OnDestroy,
  QueryList,
  ViewChild,
  ViewEncapsulation,
  afterRenderEffect,
  computed,
  contentChild,
  effect,
  inject,
  signal,
  viewChild,
} from '@angular/core';
import {AbstractControlDirective, ValidatorFn} from '@angular/forms';
import {Subject, Subscription, merge} from 'rxjs';
import {filter, map, pairwise, startWith, takeUntil} from 'rxjs/operators';
import {ThemePalette, _animationsDisabled} from '../core';
import {MAT_ERROR, MatError} from './directives/error';
import {
  FLOATING_LABEL_PARENT,
  FloatingLabelParent,
  MatFormFieldFloatingLabel,
} from './directives/floating-label';
import {MatHint} from './directives/hint';
import {MatLabel} from './directives/label';
import {MatFormFieldLineRipple} from './directives/line-ripple';
import {MatFormFieldNotchedOutline} from './directives/notched-outline';
import {MAT_PREFIX, MatPrefix} from './directives/prefix';
import {MAT_SUFFIX, MatSuffix} from './directives/suffix';
import {MatFormFieldControl as _MatFormFieldControl} from './form-field-control';
import {
  getMatFormFieldDuplicatedHintError,
  getMatFormFieldMissingControlError,
} from './form-field-errors';

/** Type for the available floatLabel values. */
export type FloatLabelType = 'always' | 'auto';

/** Possible appearance styles for the form field. */
export type MatFormFieldAppearance = 'fill' | 'outline';

/** Behaviors for how the subscript height is set. */
export type SubscriptSizing = 'fixed' | 'dynamic';

/**
 * Represents the default options for the form field that can be configured
 * using the `MAT_FORM_FIELD_DEFAULT_OPTIONS` injection token.
 */
export interface MatFormFieldDefaultOptions {
  /** Default form field appearance style. */
  appearance?: MatFormFieldAppearance;
  /**
   * Default theme color of the form field. This API is supported in M2 themes only, it has no
   * effect in M3 themes. For color customization in M3, see https://material.angular.dev/components/form-field/styling.
   *
   * For information on applying color variants in M3, see
   * https://material.angular.dev/guide/material-2-theming#optional-add-backwards-compatibility-styles-for-color-variants
   */
  color?: ThemePalette;
  /** Whether the required marker should be hidden by default. */
  hideRequiredMarker?: boolean;
  /**
   * Whether the label for form fields should by default float `always`,
   * `never`, or `auto` (only when necessary).
   */
  floatLabel?: FloatLabelType;
  /** Whether the form field should reserve space for one line by default. */
  subscriptSizing?: SubscriptSizing;
}

/**
 * Injection token that can be used to inject an instances of `MatFormField`. It serves
 * as alternative token to the actual `MatFormField` class which would cause unnecessary
 * retention of the `MatFormField` class and its component metadata.
 */
export const MAT_FORM_FIELD = new InjectionToken<MatFormField>('MatFormField');

/**
 * Injection token that can be used to configure the
 * default options for all form field within an app.
 */
export const MAT_FORM_FIELD_DEFAULT_OPTIONS = new InjectionToken<MatFormFieldDefaultOptions>(
  'MAT_FORM_FIELD_DEFAULT_OPTIONS',
);

/** Styles that are to be applied to the label elements in the outlined appearance. */
type OutlinedLabelStyles =
  [floatingLabelTransform: string, notchedOutlineWidth: number | null] | null;

/** Default appearance used by the form field. */
const DEFAULT_APPEARANCE: MatFormFieldAppearance = 'fill';

/**
 * Whether the label for form fields should by default float `always`,
 * `never`, or `auto`.
 */
const DEFAULT_FLOAT_LABEL: FloatLabelType = 'auto';

/** Default way that the subscript element height is set. */
const DEFAULT_SUBSCRIPT_SIZING: SubscriptSizing = 'fixed';

/**
 * Default transform for docked floating labels in a MDC text-field. This value has been
 * extracted from the MDC text-field styles because we programmatically modify the docked
 * label transform, but do not want to accidentally discard the default label transform.
 */
const FLOATING_LABEL_DEFAULT_DOCKED_TRANSFORM = `translateY(-50%)`;

/**
 * Despite `MatFormFieldControl` being an abstract class, most of our usages enforce its shape
 * using `implements` instead of `extends`. This appears to be problematic when Closure compiler
 * is configured to use type information to rename properties, because it can't figure out which
 * class properties are coming from. This interface seems to work around the issue while preserving
 * our type safety (alternative being using `any` everywhere).
 * @docs-private
 */
interface MatFormFieldControl<T> extends _MatFormFieldControl<T> {}

/** Container for form controls that applies Material Design styling and behavior. */
@Component({
  selector: 'mat-form-field',
  exportAs: 'matFormField',
  templateUrl: './form-field.html',
  styleUrl: './form-field.css',
  host: {
    'class': 'mat-mdc-form-field',
    '[class.mat-mdc-form-field-label-always-float]': '_shouldAlwaysFloat()',
    '[class.mat-mdc-form-field-has-icon-prefix]': '_hasIconPrefix',
    '[class.mat-mdc-form-field-has-icon-suffix]': '_hasIconSuffix',
    // Note that these classes reuse the same names as the non-MDC version, because they can be
    // considered a public API since custom form controls may use them to style themselves.
    // See https://github.com/angular/components/pull/20502#discussion_r486124901.
    '[class.mat-form-field-invalid]': '_control.errorState',
    '[class.mat-form-field-disabled]': '_control.disabled',
    '[class.mat-form-field-autofilled]': '_control.autofilled',
    '[class.mat-form-field-appearance-fill]': 'appearance == "fill"',
    '[class.mat-form-field-appearance-outline]': 'appearance == "outline"',
    '[class.mat-form-field-hide-placeholder]': '_hasFloatingLabel() && !_shouldLabelFloat()',
    '[class.mat-primary]': 'color !== "accent" && color !== "warn"',
    '[class.mat-accent]': 'color === "accent"',
    '[class.mat-warn]': 'color === "warn"',
    '[class.ng-untouched]': '_shouldForward("untouched")',
    '[class.ng-touched]': '_shouldForward("touched")',
    '[class.ng-pristine]': '_shouldForward("pristine")',
    '[class.ng-dirty]': '_shouldForward("dirty")',
    '[class.ng-valid]': '_shouldForward("valid")',
    '[class.ng-invalid]': '_shouldForward("invalid")',
    '[class.ng-pending]': '_shouldForward("pending")',
  },
  encapsulation: ViewEncapsulation.None,
  providers: [
    {provide: MAT_FORM_FIELD, useExisting: MatFormField},
    {provide: FLOATING_LABEL_PARENT, useExisting: MatFormField},
  ],
  imports: [
    MatFormFieldFloatingLabel,
    MatFormFieldNotchedOutline,
    NgTemplateOutlet,
    MatFormFieldLineRipple,
    MatHint,
  ],
})
export class MatFormField
  implements FloatingLabelParent, AfterContentInit, AfterContentChecked, AfterViewInit, OnDestroy
{
  _elementRef = inject(ElementRef);
  private _changeDetectorRef = inject(ChangeDetectorRef);
  private _platform = inject(Platform);
  private _idGenerator = inject(_IdGenerator);
  private _ngZone = inject(NgZone);
  private _defaults = inject<MatFormFieldDefaultOptions>(MAT_FORM_FIELD_DEFAULT_OPTIONS, {
    optional: true,
  });
  private _currentDirection!: Direction;

  @ViewChild('textField') _textField!: ElementRef<HTMLElement>;
  @ViewChild('iconPrefixContainer') _iconPrefixContainer!: ElementRef<HTMLElement>;
  @ViewChild('textPrefixContainer') _textPrefixContainer!: ElementRef<HTMLElement>;
  @ViewChild('iconSuffixContainer') _iconSuffixContainer!: ElementRef<HTMLElement>;
  @ViewChild('textSuffixContainer') _textSuffixContainer!: ElementRef<HTMLElement>;
  @ViewChild(MatFormFieldFloatingLabel) _floatingLabel: MatFormFieldFloatingLabel | undefined;
  @ViewChild(MatFormFieldNotchedOutline) _notchedOutline: MatFormFieldNotchedOutline | undefined;
  @ViewChild(MatFormFieldLineRipple) _lineRipple: MatFormFieldLineRipple | undefined;

  private _iconPrefixContainerSignal = viewChild<ElementRef<HTMLElement>>('iconPrefixContainer');
  private _textPrefixContainerSignal = viewChild<ElementRef<HTMLElement>>('textPrefixContainer');
  private _iconSuffixContainerSignal = viewChild<ElementRef<HTMLElement>>('iconSuffixContainer');
  private _textSuffixContainerSignal = viewChild<ElementRef<HTMLElement>>('textSuffixContainer');
  private _prefixSuffixContainers = computed(() => {
    return [
      this._iconPrefixContainerSignal(),
      this._textPrefixContainerSignal(),
      this._iconSuffixContainerSignal(),
      this._textSuffixContainerSignal(),
    ]
      .map(container => container?.nativeElement)
      .filter(e => e !== undefined);
  });

  @ContentChild(_MatFormFieldControl) _formFieldControl!: MatFormFieldControl<any>;
  @ContentChildren(MAT_PREFIX, {descendants: true}) _prefixChildren!: QueryList<MatPrefix>;
  @ContentChildren(MAT_SUFFIX, {descendants: true}) _suffixChildren!: QueryList<MatSuffix>;
  @ContentChildren(MAT_ERROR, {descendants: true}) _errorChildren!: QueryList<MatError>;
  @ContentChildren(MatHint, {descendants: true}) _hintChildren!: QueryList<MatHint>;

  private readonly _labelChild = contentChild(MatLabel);

  /** Whether the required marker should be hidden. */
  @Input()
  get hideRequiredMarker(): boolean {
    return this._hideRequiredMarker;
  }
  set hideRequiredMarker(value: BooleanInput) {
    this._hideRequiredMarker = coerceBooleanProperty(value);
  }
  private _hideRequiredMarker = false;

  /**
   * Theme color of the form field. This API is supported in M2 themes only, it
   * has no effect in M3 themes. For color customization in M3, see https://material.angular.dev/components/form-field/styling.
   *
   * For information on applying color variants in M3, see
   * https://material.angular.dev/guide/material-2-theming#optional-add-backwards-compatibility-styles-for-color-variants
   */
  @Input() color: ThemePalette = 'primary';

  /** Whether the label should always float or float as the user types. */
  @Input()
  get floatLabel(): FloatLabelType {
    return this._floatLabel || this._defaults?.floatLabel || DEFAULT_FLOAT_LABEL;
  }
  set floatLabel(value: FloatLabelType) {
    if (value !== this._floatLabel) {
      this._floatLabel = value;
      // For backwards compatibility. Custom form field controls or directives might set
      // the "floatLabel" input and expect the form field view to be updated automatically.
      // e.g. autocomplete trigger. Ideally we'd get rid of this and the consumers would just
      // emit the "stateChanges" observable. TODO(devversion): consider removing.
      this._changeDetectorRef.markForCheck();
    }
  }
  private _floatLabel!: FloatLabelType;

  /** The form field appearance style. */
  @Input()
  get appearance(): MatFormFieldAppearance {
    return this._appearanceSignal();
  }
  set appearance(value: MatFormFieldAppearance) {
    const newAppearance = value || this._defaults?.appearance || DEFAULT_APPEARANCE;
    if (typeof ngDevMode === 'undefined' || ngDevMode) {
      if (newAppearance !== 'fill' && newAppearance !== 'outline') {
        throw new Error(
          `MatFormField: Invalid appearance "${newAppearance}", valid values are "fill" or "outline".`,
        );
      }
    }
    this._appearanceSignal.set(newAppearance);
  }
  private _appearanceSignal = signal<MatFormFieldAppearance>(DEFAULT_APPEARANCE);

  /**
   * Whether the form field should reserve space for one line of hint/error text (default)
   * or to have the spacing grow from 0px as needed based on the size of the hint/error content.
   * Note that when using dynamic sizing, layout shifts will occur when hint/error text changes.
   */
  @Input()
  get subscriptSizing(): SubscriptSizing {
    return this._subscriptSizing || this._defaults?.subscriptSizing || DEFAULT_SUBSCRIPT_SIZING;
  }
  set subscriptSizing(value: SubscriptSizing) {
    this._subscriptSizing = value || this._defaults?.subscriptSizing || DEFAULT_SUBSCRIPT_SIZING;
  }
  private _subscriptSizing: SubscriptSizing | null = null;

  /** Text for the form field hint. */
  @Input()
  get hintLabel(): string {
    return this._hintLabel;
  }
  set hintLabel(value: string) {
    this._hintLabel = value;
    this._processHints();
  }
  private _hintLabel = '';

  _hasIconPrefix = false;
  _hasTextPrefix = false;
  _hasIconSuffix = false;
  _hasTextSuffix = false;

  // Unique id for the internal form field label.
  readonly _labelId = this._idGenerator.getId('mat-mdc-form-field-label-');

  // Unique id for the hint label.
  readonly _hintLabelId = this._idGenerator.getId('mat-mdc-hint-');

  // Ids obtained from the error and hint fields
  private _describedByIds: string[] | undefined;

  /** Gets the current form field control */
  get _control(): MatFormFieldControl<any> {
    return this._explicitFormFieldControl || this._formFieldControl;
  }
  set _control(value) {
    this._explicitFormFieldControl = value;
  }

  private _destroyed = new Subject<void>();
  private _isFocused: boolean | null = null;
  private _explicitFormFieldControl!: MatFormFieldControl<any>;
  private _previousControl: MatFormFieldControl<unknown> | null = null;
  private _previousControlValidatorFn: ValidatorFn | null = null;
  private _stateChanges: Subscription | undefined;
  private _valueChanges: Subscription | undefined;
  private _describedByChanges: Subscription | undefined;
  private _outlineLabelOffsetResizeObserver: ResizeObserver | null = null;
  protected readonly _animationsDisabled = _animationsDisabled();

  constructor() {
    const defaults = this._defaults;
    const dir = inject(Directionality);

    if (defaults) {
      if (defaults.appearance) {
        this.appearance = defaults.appearance;
      }
      this._hideRequiredMarker = Boolean(defaults?.hideRequiredMarker);
      if (defaults.color) {
        this.color = defaults.color;
      }
    }

    // We need this value inside a `afterRenderEffect`, however at the time of writing, reading the
    // signal directly causes a memory leak (see https://github.com/angular/angular/issues/62980).
    // TODO(crisbeto): clean this up once the framework issue is resolved.
    effect(() => (this._currentDirection = dir.valueSignal()));
    this._syncOutlineLabelOffset();
  }

  ngAfterViewInit() {
    // Initial focus state sync. This happens rarely, but we want to account for
    // it in case the form field control has "focused" set to true on init.
    this._updateFocusState();

    if (!this._animationsDisabled) {
      this._ngZone.runOutsideAngular(() => {
        // Enable animations after a certain amount of time so that they don't run on init.
        setTimeout(() => {
          this._elementRef.nativeElement.classList.add('mat-form-field-animations-enabled');
        }, 300);
      });
    }

    // Because the above changes a value used in the template after it was checked, we need
    // to trigger CD or the change might not be reflected if there is no other CD scheduled.
    this._changeDetectorRef.detectChanges();
  }

  ngAfterContentInit() {
    this._assertFormFieldControl();
    this._initializeSubscript();
    this._initializePrefixAndSuffix();
  }

  ngAfterContentChecked() {
    this._assertFormFieldControl();

    // if form field was being used with an input in first place and then replaced by other
    // component such as select.
    if (this._control !== this._previousControl) {
      this._initializeControl(this._previousControl);

      // keep a reference for last validator we had.
      if (this._control.ngControl && this._control.ngControl.control) {
        this._previousControlValidatorFn = this._control.ngControl.control.validator;
      }

      this._previousControl = this._control;
      this._changeDetectorRef.markForCheck();
    }

    // make sure the the control has been initialized.
    if (this._control.ngControl && this._control.ngControl.control) {
      // get the validators for current control.
      const validatorFn = this._control.ngControl.control.validator;

      // if our current validatorFn isn't equal to it might be we are CD behind, marking the
      // component will allow us to catch up.
      if (validatorFn !== this._previousControlValidatorFn) {
        this._changeDetectorRef.markForCheck();
      }
    }
  }

  ngOnDestroy() {
    this._outlineLabelOffsetResizeObserver?.disconnect();
    this._stateChanges?.unsubscribe();
    this._valueChanges?.unsubscribe();
    this._describedByChanges?.unsubscribe();
    this._destroyed.next();
    this._destroyed.complete();
  }

  /**
   * Gets the id of the label element. If no label is present, returns `null`.
   */
  getLabelId = computed(() => (this._hasFloatingLabel() ? this._labelId : null));

  /**
   * Gets an ElementRef for the element that a overlay attached to the form field
   * should be positioned relative to.
   */
  getConnectedOverlayOrigin(): ElementRef {
    return this._textField || this._elementRef;
  }

  /** Animates the placeholder up and locks it in position. */
  _animateAndLockLabel(): void {
    // This is for backwards compatibility only. Consumers of the form field might use
    // this method. e.g. the autocomplete trigger. This method has been added to the non-MDC
    // form field because setting "floatLabel" to "always" caused the label to float without
    // animation. This is different in MDC where the label always animates, so this method
    // is no longer necessary. There doesn't seem any benefit in adding logic to allow changing
    // the floating label state without animations. The non-MDC implementation was inconsistent
    // because it always animates if "floatLabel" is set away from "always".
    // TODO(devversion): consider removing this method when releasing the MDC form field.
    if (this._hasFloatingLabel()) {
      this.floatLabel = 'always';
    }
  }

  /** Initializes the registered form field control. */
  private _initializeControl(previousControl: MatFormFieldControl<unknown> | null) {
    const control = this._control;
    const classPrefix = 'mat-mdc-form-field-type-';

    if (previousControl) {
      this._elementRef.nativeElement.classList.remove(classPrefix + previousControl.controlType);
    }

    if (control.controlType) {
      this._elementRef.nativeElement.classList.add(classPrefix + control.controlType);
    }

    // Subscribe to changes in the child control state in order to update the form field UI.
    this._stateChanges?.unsubscribe();
    this._stateChanges = control.stateChanges.subscribe(() => {
      this._updateFocusState();
      this._changeDetectorRef.markForCheck();
    });

    // Updating the `aria-describedby` touches the DOM. Only do it if it actually needs to change.
    this._describedByChanges?.unsubscribe();
    this._describedByChanges = control.stateChanges
      .pipe(
        startWith([undefined, undefined] as const),
        map(() => [control.errorState, control.userAriaDescribedBy] as const),
        pairwise(),
        filter(([[prevErrorState, prevDescribedBy], [currentErrorState, currentDescribedBy]]) => {
          return prevErrorState !== currentErrorState || prevDescribedBy !== currentDescribedBy;
        }),
      )
      .subscribe(() => this._syncDescribedByIds());

    this._valueChanges?.unsubscribe();

    // Run change detection if the value changes.
    if (control.ngControl && control.ngControl.valueChanges) {
      this._valueChanges = control.ngControl.valueChanges
        .pipe(takeUntil(this._destroyed))
        .subscribe(() => this._changeDetectorRef.markForCheck());
    }
  }

  private _checkPrefixAndSuffixTypes() {
    this._hasIconPrefix = !!this._prefixChildren.find(p => !p._isText);
    this._hasTextPrefix = !!this._prefixChildren.find(p => p._isText);
    this._hasIconSuffix = !!this._suffixChildren.find(s => !s._isText);
    this._hasTextSuffix = !!this._suffixChildren.find(s => s._isText);
  }

  /** Initializes the prefix and suffix containers. */
  private _initializePrefixAndSuffix() {
    this._checkPrefixAndSuffixTypes();
    // Mark the form field as dirty whenever the prefix or suffix children change. This
    // is necessary because we conditionally display the prefix/suffix containers based
    // on whether there is projected content.
    merge(this._prefixChildren.changes, this._suffixChildren.changes).subscribe(() => {
      this._checkPrefixAndSuffixTypes();
      this._changeDetectorRef.markForCheck();
    });
  }

  /**
   * Initializes the subscript by validating hints and synchronizing "aria-describedby" ids
   * with the custom form field control. Also subscribes to hint and error changes in order
   * to be able to validate and synchronize ids on change.
   */
  private _initializeSubscript() {
    // Re-validate when the number of hints changes.
    this._hintChildren.changes.subscribe(() => {
      this._processHints();
      this._changeDetectorRef.markForCheck();
    });

    // Update the aria-described by when the number of errors changes.
    this._errorChildren.changes.subscribe(() => {
      this._syncDescribedByIds();
      this._changeDetectorRef.markForCheck();
    });

    // Initial mat-hint validation and subscript describedByIds sync.
    this._validateHints();
    this._syncDescribedByIds();
  }

  /** Throws an error if the form field's control is missing. */
  private _assertFormFieldControl() {
    if (!this._control && (typeof ngDevMode === 'undefined' || ngDevMode)) {
      throw getMatFormFieldMissingControlError();
    }
  }

  private _updateFocusState() {
    const controlFocused = this._control.focused;

    // Usually the MDC foundation would call "activateFocus" and "deactivateFocus" whenever
    // certain DOM events are emitted. This is not possible in our implementation of the
    // form field because we support abstract form field controls which are not necessarily
    // of type input, nor do we have a reference to a native form field control element. Instead
    // we handle the focus by checking if the abstract form field control focused state changes.
    if (controlFocused && !this._isFocused) {
      this._isFocused = true;
      this._lineRipple?.activate();
    } else if (!controlFocused && (this._isFocused || this._isFocused === null)) {
      this._isFocused = false;
      this._lineRipple?.deactivate();
    }

    this._elementRef.nativeElement.classList.toggle('mat-focused', controlFocused);
    this._textField?.nativeElement.classList.toggle('mdc-text-field--focused', controlFocused);
  }

  /**
   * The floating label in the docked state needs to account for prefixes. The horizontal offset
   * is calculated whenever the appearance changes to `outline`, the prefixes change, or when the
   * form field is added to the DOM. This method sets up all subscriptions which are needed to
   * trigger the label offset update.
   */
  private _syncOutlineLabelOffset() {
    afterRenderEffect({
      earlyRead: () => {
        if (this._appearanceSignal() !== 'outline') {
          this._outlineLabelOffsetResizeObserver?.disconnect();
          return null;
        }

        // Setup a resize observer to monitor changes to the size of the prefix / suffix and
        // readjust the label offset.
        if (globalThis.ResizeObserver) {
          this._outlineLabelOffsetResizeObserver ||= new globalThis.ResizeObserver(() => {
            this._writeOutlinedLabelStyles(this._getOutlinedLabelOffset());
          });
          for (const el of this._prefixSuffixContainers()) {
            this._outlineLabelOffsetResizeObserver.observe(el, {box: 'border-box'});
          }
        }

        return this._getOutlinedLabelOffset();
      },
      write: labelStyles => this._writeOutlinedLabelStyles(labelStyles()),
    });
  }

  /** Whether the floating label should always float or not. */
  _shouldAlwaysFloat() {
    return this.floatLabel === 'always';
  }

  _hasOutline() {
    return this.appearance === 'outline';
  }

  /**
   * Whether the label should display in the infix. Labels in the outline appearance are
   * displayed as part of the notched-outline and are horizontally offset to account for
   * form field prefix content. This won't work in server side rendering since we cannot
   * measure the width of the prefix container. To make the docked label appear as if the
   * right offset has been calculated, we forcibly render the label inside the infix. Since
   * the label is part of the infix, the label cannot overflow the prefix content.
   */
  _forceDisplayInfixLabel() {
    return !this._platform.isBrowser && this._prefixChildren.length && !this._shouldLabelFloat();
  }

  _hasFloatingLabel = computed(() => !!this._labelChild());

  _shouldLabelFloat(): boolean {
    if (!this._hasFloatingLabel()) {
      return false;
    }
    return this._control.shouldLabelFloat || this._shouldAlwaysFloat();
  }

  /**
   * Determines whether a class from the AbstractControlDirective
   * should be forwarded to the host element.
   */
  _shouldForward(prop: keyof AbstractControlDirective): boolean {
    const control = this._control ? this._control.ngControl : null;
    return control && control[prop];
  }

  /** Gets the type of subscript message to render (error or hint). */
  _getSubscriptMessageType(): 'error' | 'hint' {
    return this._errorChildren && this._errorChildren.length > 0 && this._control.errorState
      ? 'error'
      : 'hint';
  }

  /** Handle label resize events. */
  _handleLabelResized() {
    this._refreshOutlineNotchWidth();
  }

  /** Refreshes the width of the outline-notch, if present. */
  _refreshOutlineNotchWidth() {
    if (!this._hasOutline() || !this._floatingLabel || !this._shouldLabelFloat()) {
      this._notchedOutline?._setNotchWidth(0);
    } else {
      this._notchedOutline?._setNotchWidth(this._floatingLabel.getWidth());
    }
  }

  /** Does any extra processing that is required when handling the hints. */
  private _processHints() {
    this._validateHints();
    this._syncDescribedByIds();
  }

  /**
   * Ensure that there is a maximum of one of each "mat-hint" alignment specified. The hint
   * label specified set through the input is being considered as "start" aligned.
   *
   * This method is a noop if Angular runs in production mode.
   */
  private _validateHints() {
    if (this._hintChildren && (typeof ngDevMode === 'undefined' || ngDevMode)) {
      let startHint: MatHint;
      let endHint: MatHint;
      this._hintChildren.forEach((hint: MatHint) => {
        if (hint.align === 'start') {
          if (startHint || this.hintLabel) {
            throw getMatFormFieldDuplicatedHintError('start');
          }
          startHint = hint;
        } else if (hint.align === 'end') {
          if (endHint) {
            throw getMatFormFieldDuplicatedHintError('end');
          }
          endHint = hint;
        }
      });
    }
  }

  /**
   * Sets the list of element IDs that describe the child control. This allows the control to update
   * its `aria-describedby` attribute accordingly.
   */
  private _syncDescribedByIds() {
    if (this._control) {
      let ids: string[] = [];

      // TODO(wagnermaciel): Remove the type check when we find the root cause of this bug.
      if (
        this._control.userAriaDescribedBy &&
        typeof this._control.userAriaDescribedBy === 'string'
      ) {
        ids.push(...this._control.userAriaDescribedBy.split(' '));
      }

      if (this._getSubscriptMessageType() === 'hint') {
        const startHint = this._hintChildren
          ? this._hintChildren.find(hint => hint.align === 'start')
          : null;
        const endHint = this._hintChildren
          ? this._hintChildren.find(hint => hint.align === 'end')
          : null;

        if (startHint) {
          ids.push(startHint.id);
        } else if (this._hintLabel) {
          ids.push(this._hintLabelId);
        }

        if (endHint) {
          ids.push(endHint.id);
        }
      } else if (this._errorChildren) {
        ids.push(...this._errorChildren.map(error => error.id));
      }

      const existingDescribedBy = this._control.describedByIds;
      let toAssign: string[];

      // In some cases there might be some `aria-describedby` IDs that were assigned directly,
      // like by the `AriaDescriber` (see #30011). Attempt to preserve them by taking the previous
      // attribute value and filtering out the IDs that came from the previous `setDescribedByIds`
      // call. Note the `|| ids` here allows us to avoid duplicating IDs on the first render.
      if (existingDescribedBy) {
        const exclude = this._describedByIds || ids;
        toAssign = ids.concat(existingDescribedBy.filter(id => id && !exclude.includes(id)));
      } else {
        toAssign = ids;
      }

      this._control.setDescribedByIds(toAssign);
      this._describedByIds = ids;
    }
  }

  /**
   * Calculates the horizontal offset of the label in the outline appearance. In the outline
   * appearance, the notched-outline and label are not relative to the infix container because
   * the outline intends to surround prefixes, suffixes and the infix. This means that the
   * floating label by default overlaps prefixes in the docked state. To avoid this, we need to
   * horizontally offset the label by the width of the prefix container. The MDC text-field does
   * not need to do this because they use a fixed width for prefixes. Hence, they can simply
   * incorporate the horizontal offset into their default text-field styles.
   */
  private _getOutlinedLabelOffset(): OutlinedLabelStyles {
    if (!this._hasOutline() || !this._floatingLabel) {
      return null;
    }
    // If no prefix is displayed, reset the outline label offset from potential
    // previous label offset updates.
    if (!this._iconPrefixContainer && !this._textPrefixContainer) {
      return ['', null];
    }
    // If the form field is not attached to the DOM yet (e.g. in a tab), we defer
    // the label offset update until the zone stabilizes.
    if (!this._isAttachedToDom()) {
      return null;
    }
    const iconPrefixContainer = this._iconPrefixContainer?.nativeElement;
    const textPrefixContainer = this._textPrefixContainer?.nativeElement;
    const iconSuffixContainer = this._iconSuffixContainer?.nativeElement;
    const textSuffixContainer = this._textSuffixContainer?.nativeElement;
    const iconPrefixContainerWidth = iconPrefixContainer?.getBoundingClientRect().width ?? 0;
    const textPrefixContainerWidth = textPrefixContainer?.getBoundingClientRect().width ?? 0;
    const iconSuffixContainerWidth = iconSuffixContainer?.getBoundingClientRect().width ?? 0;
    const textSuffixContainerWidth = textSuffixContainer?.getBoundingClientRect().width ?? 0;
    // If the directionality is RTL, the x-axis transform needs to be inverted. This
    // is because `transformX` does not change based on the page directionality.
    const negate = this._currentDirection === 'rtl' ? '-1' : '1';
    const prefixWidth = `${iconPrefixContainerWidth + textPrefixContainerWidth}px`;
    const labelOffset = `var(--mat-mdc-form-field-label-offset-x, 0px)`;
    const labelHorizontalOffset = `calc(${negate} * (${prefixWidth} + ${labelOffset}))`;

    // Update the translateX of the floating label to account for the prefix container,
    // but allow the CSS to override this setting via a CSS variable when the label is
    // floating.
    const floatingLabelTransform =
      'var(--mat-mdc-form-field-label-transform, ' +
      `${FLOATING_LABEL_DEFAULT_DOCKED_TRANSFORM} translateX(${labelHorizontalOffset}))`;

    // Prevent the label from overlapping the suffix when in resting position.
    const notchedOutlineWidth =
      iconPrefixContainerWidth +
      textPrefixContainerWidth +
      iconSuffixContainerWidth +
      textSuffixContainerWidth;

    return [floatingLabelTransform, notchedOutlineWidth];
  }

  /** Writes the styles produced by `_getOutlineLabelOffset` synchronously to the DOM. */
  private _writeOutlinedLabelStyles(styles: OutlinedLabelStyles): void {
    if (styles !== null) {
      const [floatingLabelTransform, notchedOutlineWidth] = styles;

      if (this._floatingLabel) {
        this._floatingLabel.element.style.transform = floatingLabelTransform;
      }

      if (notchedOutlineWidth !== null) {
        this._notchedOutline?._setMaxWidth(notchedOutlineWidth);
      }
    }
  }

  /** Checks whether the form field is attached to the DOM. */
  private _isAttachedToDom(): boolean {
    const element: HTMLElement = this._elementRef.nativeElement;
    if (element.getRootNode) {
      const rootNode = element.getRootNode();
      // If the element is inside the DOM the root node will be either the document
      // or the closest shadow root, otherwise it'll be the element itself.
      return rootNode && rootNode !== element;
    }
    // Otherwise fall back to checking if it's in the document. This doesn't account for
    // shadow DOM, however browser that support shadow DOM should support `getRootNode` as well.
    return document.documentElement!.contains(element);
  }
}