foo

decorator.ts

export function ContentChildrenChanges() {

  return function (target, propertyKey) {

    if (!isContentChanges(target)) {
      return;
    }

    // Grab reference to toriginal `ngOnDestroy()` hook
    const proto = target.constructor.prototype;
    const originalNgAfterContentInit = proto.ngAfterContentInit;
    const originalNgOnDestroy = proto.ngOnDestroy;
    const subs: Subscription[] = [];

    proto.ngAfterContentInit = function () {
      const propertyValue = this[propertyKey];
      if (isQueryList(propertyValue)) {
        subs.push(propertyValue.changes.subscribe(() => {
          const change = {};
          change[propertyKey] = propertyValue;
          target.uOnContentChanges(change);
        }));

        const change = {};
        change[propertyKey] = propertyValue;
        target.uOnContentChanges(change);
      }

      callLifecycleHook(originalNgAfterContentInit, this, arguments);
    };

    proto.ngOnDestroy = function () {
      // Try to unsubscribe
      subs.forEach(sub => sub.unsubscribe());

      // Call the original `ngOnDestroy()` hook
      callLifecycleHook(originalNgOnDestroy, this, arguments);
    };

  };
}

export function ViewChildrenChanges() {

  return function (target, propertyKey) {

    if (!isViewChanges(target)) {
      return;
    }

    // Grab reference to toriginal `ngOnDestroy()` hook
    const proto = target.constructor.prototype;
    const originalNgAfterViewInit = proto.ngAfterViewInit;
    const originalNgOnDestroy = proto.ngOnDestroy;
    const subs: Subscription[] = [];

    proto.ngAfterViewInit = function () {
      const propertyValue = this[propertyKey];
      if (isQueryList(propertyValue)) {
        subs.push(propertyValue.changes.subscribe(() => {
          const change = {};
          change[propertyKey] = propertyValue;
          target.uOnViewChanges(change);
        }));

        const change = {};
        change[propertyKey] = propertyValue;
        target.uOnViewChanges(change);
      }

      callLifecycleHook(originalNgAfterViewInit, this, arguments);
    };

    proto.ngOnDestroy = function () {
      // Try to unsubscribe
      subs.forEach(sub => sub.unsubscribe());

      // Call the original `ngOnDestroy()` hook
      callLifecycleHook(originalNgOnDestroy, this, arguments);
    };

  };
}

function isQueryList(value: any): value is QueryList<any> {
  return value instanceof QueryList;
}

function callLifecycleHook(fn: any, target: any, args: any) {
  if (fn && typeof fn === 'function') {
    fn.apply(target, args);
  }
}


  
/**
 * A change reported to a lifecycle hook when a `QueryList` changes.
 *
 * See `DynamicQueries()` for more details.
 *
 * @stable
 */
export interface QueryListChange {
  [key: string]: QueryList<any>;
}

/**
 * Custom lifecycle hook that is invoked when a `QueryList` property, annotated with `@ContentChildren()`,
 * of the parent component receives changes from dynamic content.
 *
 * See `DynamicQueries()` for more details.
 *
 * @stable
 */
export interface ContentChanges {
  uOnContentChanges(change: QueryListChange);
}

/**
 * Custom lifecycle hook that is invoked when a `QueryList` property, annotated with `@ViewChildren()`,
 * of the parent component receives changes from dynamic content.
 *
 * See `DynamicQueries()` for more details.
 *
 * @stable
 */
export interface ViewChanges {
  uOnViewChanges(change: QueryListChange);
}