angular - 无法将 ChangeDetectorRef 添加为提供者

Question

我正在使用 ChangeDetectorRef 在网络请求后更新 View 。

import { Component, OnInit, ChangeDetectorRef } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { QRCodeModule } from 'angularx-qrcode';

@Component({
  selector: 'app-print',
  templateUrl: './print.component.html',
  styleUrls: ['./print.component.css'],
})
export class PrintComponent implements OnInit {
  barcodeitems;
  selecteditems = [];

  constructor(public http: HttpClient, private cdr: ChangeDetectorRef){

  }

  ngOnInit(): void {

  }

  getqr() {
    console.log("selecteditems array", this.selecteditems);
    let filterQuery = this.selecteditems.map(i => `ID eq '${i}'`).join(" or ");
    let url = `https://example.com/corporate/dev/_api/web/lists/getbytitle('Document Separator Barcodes')/items?$top=1000&$orderBy=ID&$filter=${filterQuery}`
    this.http.get(url).subscribe(data => {
      this.barcodeitems = data['value'];

      this.cdr.detectChanges();

    });
  }

}

使用 ng serve，我得到一个错误:Error: StaticInjectorError(AppModule)[PrintComponent -> ChangeDetectorRef]: StaticInjectorError(Platform: core)[PrintComponent -> ChangeDetectorRef]: NullInjectorError:没有 ChangeDetectorRef 的提供者!。

我尝试将 ChangeDetectorRef 添加到 app.module.ts 中的 providers，如下所示:

import { NgModule, ChangeDetectorRef } from '@angular/core';
.....

import { AppComponent } from './app.component';
import { PrintComponent } from './print/

print.component';

@NgModule({
  declarations: [
    AppComponent,
    PrintComponent,
  ],
  imports: [
    BrowserModule,
    HttpClientModule,
    QRCodeModule,
    FormsModule,
  ],
  providers: [PrintComponent, ChangeDetectorRef],
  bootstrap: [AppComponent]
})
export class AppModule { }

这给我一个错误:

Argument of type '{ declarations: (typeof AppComponent | typeof PrintComponent)[]; imports: (typeof BrowserModule |...' is not assignable to parameter of type 'NgModule'. Types of property 'providers' are incompatible. Type '(typeof PrintComponent | typeof ChangeDetectorRef)[]' is not assignable to type 'Provider[]'. Type 'typeof PrintComponent | typeof ChangeDetectorRef' is not assignable to type 'Provider'. Type 'typeof ChangeDetectorRef' is not assignable to type 'Provider'. Type 'typeof ChangeDetectorRef' is not assignable to type 'FactoryProvider'. Property 'provide' is missing in type 'typeof ChangeDetectorRef'.

如何将 ChangeDetectorRef 添加为提供者？

Answer 1

为什么要提供 PrintComponent？你不能提供一个组件....从你的模块中完全删除提供者，它应该可以工作。