Function _createOverlay

src/material/menu/menu-trigger-base.ts:341–357

* This method creates the overlay from the provided menu's template and saves its * OverlayRef so that it can be attached to the DOM when openMenu is called.

(menu: MatMenuPanel)

   * OverlayRef so that it can be attached to the DOM when openMenu is called.
   */
  private _createOverlay(menu: MatMenuPanel): OverlayRef {
    if (!this._overlayRef) {
      const config = this._getOverlayConfig(menu);
      this._subscribeToPositions(
        menu,
        config.positionStrategy as FlexibleConnectedPositionStrategy,
      );
      this._overlayRef = createOverlayRef(this._injector, config);
      this._overlayRef.keydownEvents().subscribe(event => {
        if (this._menu instanceof MatMenu) {
          this._menu._handleKeydown(event);
        }
      });
    }

    return this._overlayRef;
  }

  /**
   * This method builds the configuration object needed to create the overlay, the OverlayState.