Question

我一直在关注Angular Material Data Table分页器教程here。

构造分页器时，他们使用声明分页器

@ViewChild(MatPaginator) paginator: MatPaginator;

在其component.ts文件中。使用此声明，他们以后可以访问同一文件中的属性：

 ngAfterViewInit() {
        this.paginator.page
            .pipe(
                tap(() => this.loadLessonsPage())
            )
            .subscribe();
    }

没有问题。

当我在组件中执行相同的操作时：

export class AllMatchesComponent implements OnInit, OnDestroy, AfterViewInit {
...
  @ViewChild(MatPaginator) paginator: MatPaginator;
...
ngAfterViewInit(){
      console.log(this.paginator);
      this.paginator.page
        .pipe(
          tap(()=> this.loadMatchesPage())
        )
        .subscribe();
    }
...

，我在控制台中收到以下错误：

错误TypeError：无法读取未定义的属性“页面” 在AllMatchesComponent.ngAfterViewInit（all-matches.component.ts：50）

当我尝试看一下他们的示例repo（转到分支2-data-table-finished）时，该代码包含了所有过滤和排序语法，而我在其中未涉及本教程呢。换句话说，他们的示例代码与本教程中的步骤不一样，并且没有其他分支可以更简单的状态捕获代码。

我不知道为什么未定义分页器。有什么想法吗？

我的个人仓库可以在这里找到：

git clone https://github.com/Atticus29/dataJitsu.git
cd dataJitsu
git checkout SO-paginator-freeze

为方便起见，这是全部all-matches.component.ts：

import { Component, OnInit, OnDestroy, AfterViewInit, ViewChild } from '@angular/core';
import { D3Service } from '../d3.service';
import { DatabaseService } from '../database.service';
import { TextTransformationService } from '../text-transformation.service';
import * as firebase from 'firebase/app';
import { MatTableDataSource, MatSort } from '@angular/material';
import { MatPaginatorModule } from '@angular/material/paginator';
import { DataSource } from '@angular/cdk/table';
import {MatProgressSpinnerModule} from '@angular/material/progress-spinner';
import { MatchDataSource } from '../matchDataSource.model';
import { AuthorizationService } from '../authorization.service';
import { Subject } from 'rxjs/Subject';
import { tap } from 'rxjs/operators';
import { MatPaginator } from '@angular/material';

@Component({
  selector: 'app-all-matches',
  templateUrl: './all-matches.component.html',
  styleUrls: ['./all-matches.component.scss']
})
export class AllMatchesComponent implements OnInit, OnDestroy, AfterViewInit {
  private dataSource: MatchDataSource;
  private columnsToDisplay = ['rank','weightClass', 'ageClass','athlete1Name', 'athlete2Name', 'gender','tournamentName','location', 'date', 'matchRating', 'videoUrl']; //TODO make this dynamic somehow
  private loading = true;
  user: any = null;
  private ngUnsubscribe: Subject<void> = new Subject<void>();
  private matchCount: number;
  private pageSize: number;

  @ViewChild(MatPaginator) paginator: MatPaginator;

  constructor(private authService: AuthorizationService, private d3Service: D3Service, private dbService: DatabaseService, private textTransformationService: TextTransformationService) { }

  ngOnInit() {
    this.authService.getCurrentUser().takeUntil(this.ngUnsubscribe).subscribe(user=>{
      this.user = user;
    },err=>{
      console.log(err);
    });
    this.pageSize = 2;
    this.dataSource = new MatchDataSource(this.dbService);
    this.dataSource.loadMatches('test', '', '', 0, this.pageSize);
    this.dbService.getMatchCount().subscribe(results=>{
      this.matchCount = results;
    });
    }

    ngAfterViewInit(){
      console.log(this.paginator);
      this.paginator.page
        .pipe(
          tap(()=> this.loadMatchesPage())
        )
        .subscribe();
    }

    loadMatchesPage(){
      this.dataSource.loadMatches('TODO', '', 'asc', this.paginator.pageIndex, this.paginator.pageSize);
    }

    ngOnDestroy(){
      console.log("onDestroy is called");
      this.ngUnsubscribe.next();
      this.ngUnsubscribe.complete();
    }
}

这是相应的html：

<script type='text/javascript' src='http://d3js.org/d3.v3.min.js'></script>
<script type='text/javascript' src='https://cdn.firebase.com/v0/firebase.js'></script>
<script type='text/javascript' src='d3fire.min.js'></script>
<script type="text/javascript" src="http://mbostock.github.com/d3/d3.js?2.1.3"></script>
<script type="text/javascript" src="http://mbostock.github.com/d3/d3.geom.js?2.1.3"></script>
<script type="text/javascript" src="http://mbostock.github.com/d3/d3.layout.js?2.1.3"></script>
<br>
<div class="" *ngIf='user'>
  <div class="spinner-container" *ngIf="loading$">
        <mat-spinner id="spinner"></mat-spinner>
  </div>
  <mat-table #table [dataSource]="dataSource" class="mat-elevation-z8" *ngIf="!loading$">
    <!-- TODO add paidStatus to ngIf -->
    <ng-container matColumnDef="rank">
      <mat-header-cell *matHeaderCellDef> Rank </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.rank}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="weightClass">
      <mat-header-cell *matHeaderCellDef> Weight Class </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.weightClass}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="ageClass">
      <mat-header-cell *matHeaderCellDef> Age Class </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.ageClass}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="athlete1Name">
      <mat-header-cell *matHeaderCellDef> Athlete 1 </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.athlete1Name}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="athlete2Name">
      <mat-header-cell *matHeaderCellDef> Athlete 2 </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.athlete2Name}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="gender">
      <mat-header-cell *matHeaderCellDef> Gender </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.gender}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="location">
      <mat-header-cell *matHeaderCellDef> Location </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.location}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="tournamentName">
      <mat-header-cell *matHeaderCellDef> Tournament </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.tournamentName}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="date">
      <mat-header-cell *matHeaderCellDef> Date </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.date | date:'shortDate'}} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="videoUrl">
      <mat-header-cell *matHeaderCellDef> Video </mat-header-cell>
      <mat-cell *matCellDef="let entry"> <a href='{{entry.videoUrl}}'>Click</a> </mat-cell>
      <!-- <i class="material-icons right">video</i> -->
    </ng-container>
    <ng-container matColumnDef="matchRating">
      <mat-header-cell *matHeaderCellDef> Match Rating </mat-header-cell>
      <mat-cell *matCellDef="let entry"> {{entry.matchRating}}</mat-cell>
      <!-- <i class="material-icons right">video</i> -->
    </ng-container>

    <mat-header-row *matHeaderRowDef="columnsToDisplay"></mat-header-row>
    <mat-row *matRowDef="let row; columns: columnsToDisplay;"></mat-row>
  </mat-table>

  <mat-paginator [length]='matchCount' [pageSize]="2" [pageSizeOptions]="[2, 5, 10]"></mat-paginator>
</div>

Answer 1

根据您的模板，由于父div中的* ngif指令，尝试获取DOM中不存在的ViewChild fir元素时会遇到问题。

有一些解决方法：

您可以将* ngIf指令替换为[hidden]，该指令会隐藏父div但将其保留在dom中，因此您的ViewChild引用将起作用
如果必须坚持使用* ngIf，则比较复杂，这是为了确保子元素可以作为ElementRef捕获（为其分配ID并在由ngIf设置为true对其创建后获取引用）并使用此问题中ViewView的二传手的设置：

https://stackoverflow.com/a/41095677

制作物料分页器时无法读取未定义的属性“页面”

1 个答案: