角阵列变化检测

Question

我是 Angular 的初学者，我找不到适合我的问题的解决方案。

我有一个包含项目列表的组件（列表中的每个项目都在另一个组件中），并且第三个组件包含过滤器。过滤器包含多个复选框和一个过滤器按钮。

我将复选框状态的布尔数组从 filterComponent 通过 itemsListComponent 发送到 singleItemComponent，它工作正常。我的问题是更改检测。当我使用 NgDoCheck 时，它总是在我单击复选框和过滤器按钮而不是仅过滤器按钮时起作用。

我尝试了 NgOnChanges，但它只工作了一次，然后它没有看到数组中的值有任何变化。

这是我的 SingleItemsComponent（我想你不需要别人帮我解决这个问题）。看看这个，请告诉我解决这个问题的任何例子。

import { Component, OnInit, OnChanges,ViewChild, AfterViewInit, Inject,     Input, DoCheck, KeyValueDiffer, KeyValueDiffers, SimpleChanges, SimpleChange,     ChangeDetectionStrategy, ChangeDetectorRef, IterableDiffers } from     '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { animate, state, style, transition, trigger } from     '@angular/animations';
import { MatTableDataSource, MatPaginator, MatSort,     throwToolbarMixedModesError } from '@angular/material';
import { IPOLine } from 'src/app/models/po-line';
import { POLineService } from 'src/app/services/po-line.service';
@Component({
  selector: 'app-po-lines-list',
  templateUrl: './po-lines-list.component.html',
  styleUrls: ['./po-lines-list.component.css'],
  animations: [
    trigger('detailExpand', [
      state('collapsed', style({ height: '0px', minHeight: '0', display:     'none' })),
      state('expanded', style({ height: '*' })),
      transition('expanded <=> collapsed', animate('225ms cubic-bezier(0.4,     0.0, 0.2, 1)')),
    ]),
  ],
})
export class POLinesListComponent implements OnInit, DoCheck{
  isLogged = false;
  login: string;
  dataSource = new MatTableDataSource<IPOLine>();
  expandedElement: IPOLine;
  errorMessage: string;
  response: any;
  today = new Date(); // (1990, 0, 1);
  isLoadingList = true;

  differ: any;

  @Input() sentData: boolean[];
  _sentData = this.sentData;
  ngDoCheck(){

    var changes = this.differ.diff(this._sentData);
    if (changes){
      console.log('changes detected changes detected changes detected     changes detected changes detected ');
    }
    else
    console.log('changes not detected changes not detected changes not     detected changes not detected ');
  }


  @ViewChild(MatPaginator) paginator: MatPaginator;
  @ViewChild(MatSort) sort: MatSort;

  constructor(
    //private cd: ChangeDetectorRef,
    private differs: KeyValueDiffers,
    private _POLineService: POLineService,
    private activatedRoute: ActivatedRoute) {
      this.differ = differs.find({}).create();
  }

  ngOnInit() {
    // Assign the data to the data source for the table to render
    this.login = this.activatedRoute.snapshot.paramMap.get('login');
    this._POLineService.getUserPOLines(this.login)
      .subscribe(data => {
        this.dataSource.data = data;
          },
        error => {
          this.errorMessage = <any>error;
          this.isLoadingList = false;
        }
        ,
        () => {
          // console.log('eee' + this.dataSource.data);
          this.isLoadingList = false;
          this.dataSource.data.forEach(x => x.isExpired = new     Date(x.PromisedDate) < new Date() ? true : false);
        }
      );

    this.dataSource.paginator = this.paginator;
    this.dataSource.sort = this.sort;
  }
}

我很抱歉代码中的混乱，但我尝试了很多东西，我什至不记得是什么。感谢您的帮助。

FilterComponent.ts：

import { Component, OnInit, Output, EventEmitter, Input } from '@angular/core';

@Component({
  selector: 'app-filters',
  templateUrl: './filters.component.html',
  styleUrls: ['./filters.component.css']
})
export class FiltersComponent implements OnInit {

  @Output() filterByClass = new EventEmitter();
  filterByTTR = false;
  filterByTBR = false;
  filters:boolean[] = [];
  constructor() { }

  ngOnInit() {
  }

log() {
  if(!this.filterByTTR)
   console.log('TTR not checked');
   else
   console.log('TTR checked');
  if (!this.filterByTBR)
   console.log('TBR not checked');
   else
   console.log('TBR checked');
   this.filters[0] = this.filterByTTR;
   this.filters[1] = this.filterByTBR;

   this.filterByClass.emit(this.filters);
}

FilterComponent.html 的一部分：

<mat-card-content class="col">
<mat-checkbox [checked]="filterByTTR" (change)="filterByTTR = !filterByTTR">TTR</mat-checkbox>
<mat-checkbox [checked]="filterByTBR" (change)="filterByTBR = !filterByTBR">TBR</mat-checkbox>
<!-- <mat-checkbox [(ngModel)]="filterByTBR"ref-TBR>TBR</mat-checkbox> -->
<div class="d-flex justify-content-between">
  <button mat-raised-button  color="primary">Clear</button>
  <button mat-raised-button (click)="log()" color="primary">Apply</button>
</div>

PoLinesCompoenent.ts：

import { Component, OnInit, NgModule, ViewChild, Input } from 
'@angular/core';

@Component({
  selector: 'app-po-lines',
  templateUrl: './po-lines.component.html',
  styleUrls: ['./po-lines.component.css']
})    
export class POLinesComponent implements OnInit {
  count: boolean[];
  constructor() { }    
  ngOnInit(){}      
  displayCounter(count) {
    console.log('first value is: ' + count[0] + ' second value is: ' +     count[1]);
    this.count = count;
  }

PoLinesComponent.html：

<div class="container">
  <div class="row">
    <div class="side-bar col">
      <app-filters (data)='displayCounter($event)'></app-filters>
    </div>
    <div class="content col">
      <app-po-lines-list [sentData]="count"></app-po-lines-list>
    </div>
  </div>
</div>

Answer 1

Angular 更改检测仅检查是否通过引用更改了某些内容。在您的父组件中，您必须创建一个新数组并将其分配给变量，每当您的数组中的条目发生更改时。只需将数组视为不可变对象。

Answer 2

如果父级更改了“sentData”输入，您可以使用带输入的 setter 来检测更改。每次输入从外部更改时，都会调用 setter 函数。例如，您可以执行以下操作：

  @Input('sentData') 
  set sentData(value:any){
     //this function will be called whenever value of input changes. the value parameter will contain the new changed 
      this._sentData=value;
      //things to perform on change go here
  }
  _sentData;

有关输入更改检测的更多详细信息，请参阅此链接：Intercept @Input property change in Angular 希望这会有所帮助。

如果通过 parent 传入的值不是原始类型，则 angular 不会检测到该对象的变化，并且不会在子对象中调用 setter，即POLinesListComponent。要解决此问题并检测到您的更改，您可以使用 javascript 的 Object.assign 函数，该函数将更改 this.count 的引用，从而触发角度变化检测。 您可以在 displayCounter 函数中执行以下操作：

displayCounter(count) {
    console.log('first value is: ' + count[0] + ' second value is: ' +     count[1]);
    //if count is changed, then only trigger change.
    if(JSON.stringify(this.count)!=JSON.stringify(count))
    {

      this.count= []; 
      Object.assign(this.count, count);
    }

  }

我什至创建了一个类似于您的实现的 stackblitz，其中可以正确检测到更改，并且每次应用过滤器时都会将新计数的值记录到控制台。这里Input Change Detection for Object