* ngIf在使用可观察项时在Angular Material表中不起作用

Question

我正在尝试使用具有可扩展行的Angular Material表，仅在屏幕宽度低于特定断点时才显示信息。我正在使用可观察的isHandSetPortrait$（我正在HTML中订阅）来确定是否已达到断点。

该表有两列（ Name 和 Info ）。无论isHandsetPortrait是还是否，都会显示名称，并且仅当isHandsetPortrait$为false时显示信息。这可以按预期工作。

在可展开的行中，我有一个*ngIf，它使用相同的可观察的isHandsetPortrait$，以在isHandsetPortrait$的输出为true时显示文本。但是，这似乎不起作用。

table-expandable-rows-example.html

<!-- *ngIf works here -->
  <div *ngIf="isHandsetPortrait$ | async">ngIf works here</div>
  <div class="mat-elevation-z8">
    <table mat-table [dataSource]="dataSource" matSort matSortActive="priority" matSortDirection="desc"
           multiTemplateDataRows>


      <!-- Name Column -->
      <ng-container matColumnDef="name">
        <th mat-header-cell *matHeaderCellDef mat-sort-header> Name</th>
        <td mat-cell *matCellDef="let row"> {{row.name}}</td>
      </ng-container>

      <!-- Info Column -->
      <ng-container matColumnDef="info" >
        <th mat-header-cell *matHeaderCellDef></th>
        <td mat-cell *matCellDef="let row" class="info-cell">
          Info
        </td>
      </ng-container>

      <!-- Expanded Content Column - The detail row is made up of this one column that spans across all columns -->
      <ng-container matColumnDef="expandedDetail">
        <td mat-cell *matCellDef="let element" [attr.colspan]="displayedColumns.length">
          <div class="expanded-content" [@detailExpand]="element == expandedElement ? 'expanded' : 'collapsed'">
            Additional text....
            <!-- *ngIf does not work here -->
            <div *ngIf="isHandsetPortrait$ | async">ngIf does not work here</div>
          </div>
        </td>
      </ng-container>

      <tr mat-header-row *matHeaderRowDef="getDisplayedColumns(isHandsetPortrait$ | async)"></tr>
      <tr mat-row *matRowDef="let element; columns: getDisplayedColumns(isHandsetPortrait$ | async);"
          class="example-element-row" [class.example-expanded-row]="expandedElement === element"
          (click)="expandedElement = expandedElement === element ? null : element"></tr>
      <tr mat-row *matRowDef="let row; columns: ['expandedDetail']" class="example-detail-row"></tr>
    </table>
  </div>

table-expandable-rows-example.ts

import { Component, OnInit, ViewChild } from '@angular/core';
import { MatPaginator, MatSort, MatTableDataSource } from '@angular/material';
import { animate, state, style, transition, trigger } from '@angular/animations';
import { from, Observable, of, pipe } from 'rxjs';
import { concatMap, delay, map, share } from 'rxjs/operators';
import { BreakpointObserver, Breakpoints } from '@angular/cdk/layout';

/**
 * @title Table with expandable rows
 */
@Component({
  selector: 'table-expandable-rows-example',
  styleUrls: ['table-expandable-rows-example.css'],
  templateUrl: 'table-expandable-rows-example.html',
animations: [
    trigger('detailExpand', [
      state('collapsed', style({ height: '0px', minHeight: '0' })),
      state('expanded', style({ height: '*' })),
      transition('expanded <=> collapsed', animate('225ms cubic-bezier(0.4, 0.0, 0.2, 1)'))
    ]),
  ]
})
export class TableExpandableRowsExample {

    public isHandsetPortrait$: Observable<boolean> = this.breakpointObserver.observe(Breakpoints.HandsetPortrait)
    .pipe(
      map(orientationState => orientationState.matches),
      share()
    );

  private chatRequests = [
    {
      name: 'John Wayne'
    },
    {
      name: 'Oscar Wilde'
    },
    {
      name: 'Eric Cantona'
    }
  ];

  dataSource = new MatTableDataSource(this.chatRequests);

  displayedColumns: { def: string, isMobile: boolean }[] = [
    {
      def: 'name',
      isMobile: true
    },
    {
      def: 'info',
      isMobile: false
    }
  ];

  constructor(private breakpointObserver: BreakpointObserver) { }


  public getDisplayedColumns(isHandsetPortrait: boolean) {
    return this.displayedColumns
      .filter(cd => !isHandsetPortrait || cd.isMobile)
      .map(cd => cd.def);
  }

}

我整理了一个StackBlitz project，应该突出显示我遇到的问题。

*ngIf在表之外（html模板的第2行）工作，但在表内部（html模板的第28行）不工作。如何使第二个*ngIf工作？

Answer 1

您必须使用 shareReplay 使其起作用，使用 share 对于第二个订户将不会发生任何事情

public isHandsetPortrait$: Observable<boolean> = this.breakpointObserver.observe(Breakpoints.HandsetPortrait)
.pipe(
  map(orientationState => orientationState.matches),
  shareReplay(1) // here
);

https://stackblitz.com/edit/angular-ml4vym-71mba5