Method _setIsOpen

src/material/menu/menu.ts:474–506

(isOpen: boolean)

  }

  _setIsOpen(isOpen: boolean) {
    this._panelAnimationState = isOpen ? 'enter' : 'void';

    if (isOpen) {
      if (this._keyManager.activeItemIndex === 0) {
        // Scroll the content element to the top as soon as the animation starts. This is necessary,
        // because we move focus to the first item while it's still being animated, which can throw
        // the browser off when it determines the scroll position. Alternatively we can move focus
        // when the animation is done, however moving focus asynchronously will interrupt screen
        // readers which are in the process of reading out the menu already. We take the `element`
        // from the `event` since we can't use a `ViewChild` to access the pane.
        const menuPanel = this._resolvePanel();

        if (menuPanel) {
          menuPanel.scrollTop = 0;
        }
      }
    } else if (!this._animationsDisabled) {
      // Some apps do `* { animation: none !important; }` in tests which will prevent the
      // `animationend` event from firing. Since the exit animation is loading-bearing for
      // removing the content from the DOM, add a fallback timer.
      this._exitFallbackTimeout = setTimeout(() => this._onAnimationDone(EXIT_ANIMATION), 200);
    }

    // Animation events won't fire when animations are disabled so we simulate them.
    if (this._animationsDisabled) {
      setTimeout(() => {
        this._onAnimationDone(isOpen ? ENTER_ANIMATION : EXIT_ANIMATION);
      });
    }

    this._changeDetectorRef.markForCheck();
  }

  /**
   * Sets up a stream that will keep track of any newly-added menu items and will update the list