Angular mat-sidenav property isHandset$ | async explain

问题

<mat-sidenav-container class="sidenav-container">
  <mat-sidenav #drawer class="sidenav" fixedInViewport="true" [attr.role]="(isHandset$ | async) ? 'dialog' : 'navigation'"
    [mode]="(isHandset$ | async) ? 'push' : 'push'" [opened]="!(isHandset$ | async)">
    <mat-toolbar color="primary">Menu</mat-toolbar>
    <mat-nav-list>
      <a mat-list-item href="#">Link 1</a>
      <a mat-list-item href="#">Link 2</a>
      <a mat-list-item href="#">Link 3</a>
    </mat-nav-list>
  </mat-sidenav>

I do not understand what is written in the code (isHandset$ | async)please explain

回答1:

'Handset' is one of the breakpoint names of angular material layout. The list of breakpoint names is Handset, Tablet, Web, HandsetPortrait, TabletPortrait, WebPortrait, HandsetLandscape, TabletLandscape, WebLandscape.

Please check https://material.io/design/layout/responsive-layout-grid.html#breakpoints for more information about material layout breakpoints

In your example above, isHandset$ is coming from the corresponding component .ts file. Please look for code similar to below in your component file.

isHandset$: Observable<boolean> = this.breakpointObserver.observe(Breakpoints.Handset)
    .pipe(
      map(result => result.matches)
    );

When you resize the browser and when browser width matches with handset (mobile phone screen) width isHandset$ sets to true. ! (isHandset$ | async) in turn sets 'opened' attribute of sidenav drawer to false and collapses the sidenav drawer.

As isHandset$ is an Observable property, therefore 'async' pipe is used for the asynchronous call.

来源：https://stackoverflow.com/questions/52158521/angular-mat-sidenav-property-ishandset-async-explain