i'am working on a assignment of angular 4, i'am new to it, i'am applying pagination for mat-table,getting some problem in it, while i'am printing data to console it is displaying as below
while i'am trying to apply dataSource.data.length, getting below error.
WellComponent.html:57 ERROR TypeError: Cannot read property 'length' of undefined
at Object.View_WellComponent_0._co [as updateDirectives] (WellComponent.html:60)
at Object.debugUpdateDirectives [as updateDirectives] (core.es5.js:13075)
at checkAndUpdateView (core.es5.js:12255)
at callViewAction (core.es5.js:12620)
at execComponentViewsAction (core.es5.js:12552)
at checkAndUpdateView (core.es5.js:12261)
at callViewAction (core.es5.js:12620)
at execEmbeddedViewsAction (core.es5.js:12578)
at checkAndUpdateView (core.es5.js:12256)
at callViewAction (core.es5.js:12620)
Can i get help in this aspect, how should i access that length property.
Component:
import { MatPaginator } from '@angular/material';
import { DataSource } from '@angular/cdk/collections';
import { Component, OnInit,ViewChild,ChangeDetectorRef } from '@angular/core';
import { WellService } from '../services/well.service';
import { Well } from '../well/well';
import { Observable } from 'rxjs/Rx';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
import 'rxjs/add/operator/startWith';
import 'rxjs/add/observable/merge';
import 'rxjs/add/operator/map';
@Component({
selector: 'app-well',
templateUrl: './well.component.html',
styleUrls: ['./well.component.css'],
providers:[WellService]
})
export class WellComponent implements OnInit {
title = 'Wells';
header:string;
displayedColumns = ['active', 'company', 'country', 'well','wellbore'];
public dataSource: WellDataSource | any;
obs:any;
@ViewChild(MatPaginator) paginator : MatPaginator;
constructor(private wellService:WellService) {
this.header='assets/images/BHI_header_logo_bd.png'
}
ngOnInit() {
this.obs = this.wellService.getWells();
this.dataSource = new WellDataSource(this.obs, this.paginator);
}
}
export class WellDataSource extends DataSource<any> {
constructor(private _obs: any, private _paginator: MatPaginator) {
super();
}
connect(): Observable<any[]> {
const displayDataChanges = [
this._obs,
this._paginator.page,
];
return this._obs.flatMap(x => {
return Observable.merge(...displayDataChanges).map(() => {
const data = x.slice();
console.log(data);
const startIndex = this._paginator.pageIndex * this._paginator.pageSize;
console.log(startIndex);
console.log(this._paginator.pageSize)
console.log(this._obs);
console.log(x.slice());
return data.splice(startIndex, this._paginator.pageSize);
});
})
}
disconnect() {}
}
**HTML:**
<div>
<div class="image"><img [src]="header" ></div>
<div class="w3-display-left">
<nav>
<li><a routerLink="/wells" routerLinkActive="active">My Wells</a></li>
<li><a routerLink="/dev" routerLinkActive="active">Well Management</a></li>
<li><a routerLink="/dev" routerLinkActive="active">Admin Tools</a></li>
</nav>
<div class="w3-display-right">
<button mat-button>Reset</button>
<button mat-button>Refresh</button>
<button mat-button>View Wireline</button>
<button mat-button>Chat</button>
<button mat-button>View Seismic</button>
<button mat-button>Alerts</button>
</div>
<br>
<br>
<div>
<mat-table #table [dataSource]="dataSource">
<!-- Active -->
<ng-container matColumnDef="active">
<mat-header-cell *matHeaderCellDef> Active </mat-header-cell>
<mat-cell *matCellDef="let row"> {{row.active}} </mat-cell>
</ng-container>
<!-- Company -->
<ng-container matColumnDef="company">
<mat-header-cell *matHeaderCellDef> Company </mat-header-cell>
<mat-cell *matCellDef="let row"> {{row.company}} </mat-cell>
</ng-container>
<!-- Country -->
<ng-container matColumnDef="country">
<mat-header-cell *matHeaderCellDef>Country</mat-header-cell>
<mat-cell *matCellDef="let row"> {{row.country}} </mat-cell>
</ng-container>
<!-- Well -->
<ng-container matColumnDef="well">
<mat-header-cell *matHeaderCellDef> Well </mat-header-cell>
<mat-cell *matCellDef="let row"> {{row.well}} </mat-cell>
</ng-container>
<!-- Wellbore -->
<ng-container matColumnDef="wellbore">
<mat-header-cell *matHeaderCellDef> Wellbore </mat-header-cell>
<mat-cell *matCellDef="let row"> {{row.wellbore}} </mat-cell>
</ng-container>
<mat-header-row *matHeaderRowDef="displayedColumns"></mat-header-row>
<mat-row *matRowDef="let row; columns: displayedColumns;"></mat-row>
</mat-table>
<mat-paginator #paginator
[length]="dataSource.data.length"
[pageIndex]="0"
[pageSize]="25"
[pageSizeOptions]="[5, 10, 25, 100]">
</mat-paginator>
</div>
</div>
<div>
<router-outlet></router-outlet>
</div>
答案 0 :(得分:5)
The error is because of you are trying to access data before it available
Try to use safe operator :
dataSource.data?.length
OR
make some initialisation inside constructor
dataSource.data = [];
As per your code change [length]="dataSource.data.length"
to [length]="obs.data?.length"
, like this :
<mat-paginator #paginator
[length]="obs.data?.length"
[pageIndex]="0"
[pageSize]="25"
[pageSizeOptions]="[5, 10, 25, 100]">
</mat-paginator>
答案 1 :(得分:0)
初始化数组会导致错误消失,但是表中的数据将永远不会更新-它为空。添加问号(即dataSource.data?.length)无法正常工作,因为在其他地方还没有希望它未定义。
有些孩子叫我尝试一个BehaviorSubject。它们是始终具有价值的Observable。当您订阅时,您可以获得最新的价值。他们也是观察者,您可以告诉他们下一个值是什么。在这里阅读更多。
http://reactivex.io/rxjs/manual/overview.html#behaviorsubject
我将dataSource.data设置为BehaviorSubject,这是孩子告诉我的方式,初始值[]然后在值更改时(通过next())告诉了它。
而且,因为我正在进行排序和分页,所以我不得不更新该代码以使用this.data.getValue()而不是this.data。
答案 2 :(得分:0)
我通过两种方法解决了这个问题:
a)安全操作员
[length] =“ dataSource.data?.length”
b)正确初始化数据源(避免切片错误)
ngOnInit() {
this.dataSource = new EmplTblDataSource(this.paginator, this.sort);
this.dataSource.data=[];
}
然后,我用OnChanges
方法更新表内容