menu-position.spec.ts

import { convertMenuPositionToConnectedPositions, MenuPositionValue } from './menu-position';
import { ConnectedPosition } from '@angular/cdk/overlay';

interface TestPosition {
  side: MenuPositionValue,
  align: MenuPositionValue,
  positions: ConnectedPosition[]
}

const POSITIONS: TestPosition[] = [
  {
    side: 'top',
    align: 'left',
    positions: [
      {
        originX: 'start',
        originY: 'top',
        overlayX: 'start',
        overlayY: 'bottom',
        offsetY: 0
      }
    ]
  },
  {
    side: 'right',
    align: 'top',
    positions: [
      {
        originX: 'end',
        originY: 'top',
        overlayX: 'start',
        overlayY: 'top',
        offsetY: 0
      }
    ]
  },
  {
    side: 'left',
    align: 'bottom',
    positions: [
      {
        originX: 'start',
        originY: 'bottom',
        overlayX: 'end',
        overlayY: 'bottom',
        offsetY: 0
      }
    ]
  },
  {
    side: 'bottom',
    align: 'left',
    positions: [
      {
        originX: 'start',
        originY: 'bottom',
        overlayX: 'start',
        overlayY: 'top',
        offsetY: 0
      }
    ]
  },
  {
    side: 'bottom',
    align: 'right',
    positions: [
      {
        originX: 'end',
        originY: 'bottom',
        overlayX: 'end',
        overlayY: 'top',
        offsetY: 0
      }
    ]
  }
];

fdescribe('MenuPosition', () => {
  for (const pos of POSITIONS) {
    it(`should convert menu position [${pos.side}, ${pos.align}] to connected positions`, () => {
      const positions = convertMenuPositionToConnectedPositions([pos.side as MenuPositionValue, pos.align as MenuPositionValue]);

      // expect(positions.length).toBe(pos.positions.length);
      expect(positions[0]).toEqual(pos.positions[0]);
    });
  }
});

menu-position.ts

import { ConnectedPosition, HorizontalConnectionPos, VerticalConnectionPos } from '@angular/cdk/overlay';

export type MenuPositionValue = 'top' | 'right' | 'bottom' | 'left';
export type MenuPosition = [MenuPositionValue, MenuPositionValue];

interface ConvertedPosition extends ConnectedPosition {
  originFallbackX: HorizontalConnectionPos;
  originFallbackY: VerticalConnectionPos;
  overlayFallbackX: HorizontalConnectionPos;
  overlayFallbackY: VerticalConnectionPos;
}

function convertSideMenuPosition(side: MenuPositionValue): ConvertedPosition {
  if (side === 'top' || side === 'bottom') {
    return {
      originX: 'start',
      originY: side,
      overlayX: 'start',
      overlayY: side === 'top' ? 'bottom' : 'top',
      originFallbackX: 'end',
      originFallbackY: side === 'top' ? 'bottom' : 'top',
      overlayFallbackX: 'end',
      overlayFallbackY: side
    };
  } else {
    return {
      originX: side === 'left' ? 'start' : 'end',
      originY: 'top',
      overlayX: side === 'left' ? 'end' : 'start',
      overlayY: 'top',
      originFallbackX: side === 'left' ? 'end' : 'start',
      originFallbackY: 'bottom',
      overlayFallbackX: side === 'left' ? 'start' : 'end',
      overlayFallbackY: 'bottom'
    };
  }
}

export function convertMenuPositionToConnectedPositions([side, align]: MenuPosition, offsetY = 0): ConnectedPosition[] {
  let {
    originX,
    originY,
    overlayX,
    overlayY,
    originFallbackX,
    originFallbackY,
    overlayFallbackX,
    overlayFallbackY
  } = convertSideMenuPosition(side);

  if (align === 'top' || align === 'bottom') {
    originY = align;
    overlayY = originY;
  } else {
    originX = align === 'left' ? 'start' : 'end';
    overlayX = originX;
  }

  return [
    { originX, originY, overlayX, overlayY, offsetY },
    { originX: originFallbackX, originY, overlayX: overlayFallbackX, overlayY, offsetY },
    {
      originX,
      originY: originFallbackY,
      overlayX,
      overlayY: overlayFallbackY,
      offsetY: -offsetY
    },
    {
      originX: originFallbackX,
      originY: originFallbackY,
      overlayX: overlayFallbackX,
      overlayY: overlayFallbackY,
      offsetY: -offsetY
    }
  ];
}

trigger.directive.ts

  /**
   * Sets the appropriate positions on a position strategy
   * so the overlay connects with the trigger correctly.
   * @param positionStrategy Strategy whose position to update.
   */
  private setPosition(positionStrategy: FlexibleConnectedPositionStrategy) {
    let positions: ConnectedPosition[];

    if (this.triggersSubmenu()) {
      // When the menu is a sub-menu, it should always align itself
      // to the edges of the trigger, instead of overlapping it.
      positions = convertMenuPositionToConnectedPositions(['right', 'top'], -MENU_PANEL_TOP_PADDING);
    } else {
      positions = convertMenuPositionToConnectedPositions(this.menu.position);
    }

    positionStrategy.withPositions(positions);
  }

RTL is no requirement for me, so the code doesn't take that into account.

Hi, this looks great, can you tell us how to use this? The trigger directive doesn't look like a regular angular directive, it's not clear how we should be getting the reference to the FlexibleConnectedPositionStrategy?

@chriszrc I don't know if you still need the answer, but below is the way I used it if other people need it:

 
@ViewChildren(MatMenuTrigger)
menuTriggers: QueryList<MatMenuTrigger>;

constructor(
    private ngZone: NgZone
) { }

ngAfterViewInit(): void {

    this.menuTriggers.forEach(item => {

        item.menuOpened.pipe(
            // delay(1000)
        ).subscribe(() => {

            this.menuOpened = item;

            this.ngZone.onStable.pipe(first()).subscribe(() => {
                this.recalculateMenu(item)
            })
        });
    });
}

recalculateMenu(menuTrigger: MatMenuTrigger) {
    const overlayRef: OverlayRef = (menuTrigger as any)._overlayRef;
    const overlayConfig = overlayRef.getConfig();
    (overlayConfig.positionStrategy as any)._isInitialRender = true;
    this.setPosition(menuTrigger, overlayConfig.positionStrategy as FlexibleConnectedPositionStrategy);
    overlayConfig.positionStrategy.apply();
}

setPosition(menuTrigger: MatMenuTrigger, positionStrategy: FlexibleConnectedPositionStrategy) {

    let positions: ConnectedPosition[];

    if (menuTrigger.triggersSubmenu()) {
        // When the menu is a sub-menu, it should always align itself
        // to the edges of the trigger, instead of overlapping it.
        positions = convertMenuPositionToConnectedPositions(["right", "top"], -8);
    } else {
        positions = convertMenuPositionToConnectedPositions(["right", "top"]);
    }

    positionStrategy.withPositions(positions);
}

what is this.menuOpened?