中心垫菜单，中心垫菜单覆盖到按钮

Question

Per Material Issue 9631 将 mat-menu 居中到按钮如下。

the issue is that supporting it deviates from the spec and may end up looking weird.

---

我需要这个功能...因为编写我自己的 CDK 覆盖比覆盖 mat-menu 组件更耗时...我对重新创建 mat-menu，只需要将菜单居中...我对任何其他库的实现也不感兴趣，我想使用 Material mat-menu，所以我的问题如下。

问题：

利用 angular directive，如何覆盖 MatMenuTrigger 的私有变量和方法以将 CDK 覆盖层居中放置在按钮上？

Answer 1

我选择了一个指令，因为 MatMenuTrigger 是一个 Directive，复制 Material 源使用的逻辑是有意义的。

到目前为止，这是我想出的方法，我不确定像这样进入 class 本身是否是 "acceptable"，或者这样做是否有任何负面影响就这样。

I am open to constructive discussion on this approach for any recommendations or improvements.

---

Stackblitz

https://stackblitz.com/edit/angular-jpgjdc-nqmyht?embed=1&file=app/center-matmenu.directive.ts

本质上，我将 matMenuTrigger 与按钮分离，方法是将它放在 div 上包裹 mat-menu... 这样我就可以通过指令以编程方式打开菜单而不是按钮。

• 我还将 menuTrigger 分配给 div 上的 templateRef 并将其作为输入传递给我的 center-mat-menu 选择器

<button mat-button [center-mat-menu]="menuTrigger">Menu</button>
<div #menuTrigger="matMenuTrigger" [matMenuTriggerFor]="menu">
 <mat-menu #menu="matMenu">

从那里我通过 @HostListener

创建一个监听器

@HostListener('click', ['$event'])

然后复制 MatMenuTrigger 指令的逻辑来操纵位置、初始化菜单并在单击时触发打开动画。

这基本上是 menu-trigger.ts 源代码中 openMenu() 方法的复制，只是我在菜单初始化之后和调用 this.menuTrigger.menu['_startAnimation'](); 之前操作左侧和顶部样式打开菜单。

menu-trigger.ts

I store the dimension of the source button into variables and use that information to calculate the center point of the button, I then use that with the width of the initialized menu to calculate left

@Directive({
  selector: '[center-mat-menu]'
})
export class CenterMatmenuDirective {
  overlayRef: OverlayRef;
  overlayConf: OverlayConfig;
  dropDown: HTMLElement;
  overlayPositionBox: HTMLElement;
  menu: MatMenuPanel;
  button: HTMLElement;
  buttonWidth: number;
  buttonLeft: number;
  buttonBottom: number;

  @Input('center-mat-menu') private menuTrigger: MatMenuTrigger;

  constructor(private _menuButton: ElementRef, private _renderer: Renderer2) { }

  @HostListener('click', ['$event'])
  onclick(e) {
    this._setVariables();
    //menu not opened by keyboard down arrow, have to set this so MatMenuTrigger knows the menu was opened with a mouse click
    this.menuTrigger['_openedBy'] = e.button === 0 ? 'mouse' : null;

    this._overrideMatMenu();

    this.dropDown = this.overlayRef.overlayElement.children[0].children[0] as HTMLElement;
    this.overlayPositionBox = this.overlayRef.hostElement;

    setTimeout(() => {
      this._styleDropDown(this.dropDown);
      this._setOverlayPosition(this.dropDown, this.overlayPositionBox);
      this._openMenu();
    })
  }

  private _setVariables() {
    const config = this.menuTrigger['_getOverlayConfig']();
    this.menuTrigger['_overlayRef'] = this.menuTrigger['_overlay'].create(config);
    this.overlayRef = this.menuTrigger['_overlayRef'];
    this.overlayConf = this.overlayRef.getConfig();
    this.overlayRef.keydownEvents().subscribe();
    this.menu = this.menuTrigger.menu;
    this._setButtonVars();
  }

  private _setButtonVars() {
    this.button = this._menuButton.nativeElement;
    this.buttonWidth = this.button.getBoundingClientRect().width;
    this.buttonLeft = this.button.getBoundingClientRect().left;
    this.buttonBottom = this.button.getBoundingClientRect().bottom;
  }

  private _overrideMatMenu() {
    let strat = this.overlayConf.positionStrategy as FlexibleConnectedPositionStrategy;
    this.menuTrigger['_setPosition'](strat);
    strat.positionChanges.subscribe(() => {
      this._setButtonVars();
      this._setOverlayPosition(this.dropDown, this.overlayPositionBox);
    })
    this.overlayConf.hasBackdrop = this.menu.hasBackdrop == null ?
      !this.menuTrigger.triggersSubmenu() : this.menu.hasBackdrop;
    this.overlayRef.attach(this.menuTrigger['_getPortal']());

    if (this.menu.lazyContent) {
      this.menu.lazyContent.attach()
    }

    this.menuTrigger['_closeSubscription'] = this.menuTrigger['_menuClosingActions']().subscribe(() => {
      this.menuTrigger.closeMenu();
    });
    this.menuTrigger['_initMenu']();
  }

  private _styleDropDown(dropDown: HTMLElement) {
    this._renderer.setStyle(this._renderer.parentNode(dropDown), 'transform-origin', 'center top 0px');
  }

  private _setOverlayPosition(dropDown: HTMLElement, overlayPositionBox: HTMLElement) {
    let dropDownleft = ((this.buttonWidth / 2 + this.buttonLeft) - dropDown.offsetWidth / 2);

    this._renderer.setStyle(overlayPositionBox, 'top', this.buttonBottom + 5 + 'px');
    this._renderer.setStyle(overlayPositionBox, 'left', dropDownleft + 'px');
    this._renderer.setStyle(overlayPositionBox, 'height', '100%');
  }

  private _openMenu() {
    this.menuTrigger.menu['_startAnimation']();
  }
}