angular-docs-cn/packages/core/src/change_detection/constants.ts

/**
 * @license
 * Copyright Google Inc. 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.io/license
 */


/**
 * The strategy that the default change detector uses to detect changes.
 * When set, takes effect the next time change detection is triggered.
 *
 * @publicApi
 */
export enum ChangeDetectionStrategy {
  /**
   * Use the `CheckOnce` strategy, meaning that automatic change detection is deactivated
   * until reactivated by setting the strategy to `Default` (`CheckAlways`).
   * Change detection can still be explicitly invoked.
   */
  OnPush = 0,

  /**
   * Use the default `CheckAlways` strategy, in which change detection is automatic until
   * explicitly deactivated.
   */
  Default = 1,
}

/**
 * Defines the possible states of the default change detector.
 * @see `ChangeDetectorRef`
 */
export enum ChangeDetectorStatus {
  /**
   * A state in which, after calling `detectChanges()`, the change detector
   * state becomes `Checked`, and must be explicitly invoked or reactivated.
   */
  CheckOnce,

  /**
   * A state in which change detection is skipped until the change detector mode
   * becomes `CheckOnce`.
   */
  Checked,

  /**
   * A state in which change detection continues automatically until explicitly
   * deactivated.
   */
  CheckAlways,

  /**
   * A state in which a change detector sub tree is not a part of the main tree and
   * should be skipped.
   */
  Detached,

  /**
   * Indicates that the change detector encountered an error checking a binding
   * or calling a directive lifecycle method and is now in an inconsistent state. Change
   * detectors in this state do not detect changes.
   */
  Errored,

  /**
   * Indicates that the change detector has been destroyed.
   */
  Destroyed,
}

/**
 * Reports whether a given strategy is currently the default for change detection.
 * @param changeDetectionStrategy The strategy to check.
 * @returns True if the given strategy is the current default, false otherwise.
 * @see `ChangeDetectorStatus`
 * @see `ChangeDetectorRef`
 */
export function isDefaultChangeDetectionStrategy(changeDetectionStrategy: ChangeDetectionStrategy):
    boolean {
  return changeDetectionStrategy == null ||
      changeDetectionStrategy === ChangeDetectionStrategy.Default;
}