Question

当我尝试推送数组时，出现以下错误：

无法读取null的属性“ push”

我试图通过初始化数组来解决我的问题，但是它不起作用。抱歉，我是新手，我不明白为什么它不起作用。谢谢您的帮助。

balade.ts：

export class Balade {
  NOM_BALADE: string;
  DATE_DEPART: string;
  LIEU_RDV: string;
  ID_BALADE?: number;

  constructor(NOM_BALADE: string, DATE_DEPART: string, LIEU_RDV: string, ID_BALADE?: number) {
      this.NOM_BALADE = NOM_BALADE;
      this.DATE_DEPART = DATE_DEPART;
      this.LIEU_RDV = LIEU_RDV;
      this.ID_BALADE = ID_BALADE;
  }
}

balade.service.ts：

import { Injectable } from '@angular/core';
import { HttpClient, HttpErrorResponse, HttpParams } from '@angular/common/http';

import { Observable, throwError } from 'rxjs';
import { map, catchError } from 'rxjs/operators';

import { Balade } from './balade';

@Injectable({
  providedIn: 'root'
})
export class BaladeService {
  baseUrl = './htdocs/api';
  balades: Balade[] = [];

constructor(private http: HttpClient) { }

  getAll(): Observable<Balade[]> {
    return this.http.get(`${this.baseUrl}/list.php`).pipe(
      map((res) => {
        this.balades = res['data'];
        return this.balades;
    }),
    catchError(this.handleError));
  }

  store(balade: Balade): Observable<Balade[]> {
    return this.http.post(`${this.baseUrl}/store.php`, { data: balade })
      .pipe(map((res) => {
        this.balades.push(res['data']);
        return this.balades;
      }),
      catchError(this.handleError));
  }

app.component.ts：

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

import { Balade } from './balade';
import { BaladeService } from './balade.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
  balades: Balade[] = [];
  error = '';
  success = '';

  balade = new Balade('', '','');

  constructor(private baladeService: BaladeService) {
  }

  ngOnInit() {
    this.getBalades();
  }

  getBalades(): void {
    this.baladeService.getAll().subscribe(
      (res: Balade[]) => {
        this.balades = res;
      },
      (err) => {
        this.error = err;
      }
    );
  }

  addBalade(f) {
    this.resetErrors();

    this.baladeService.store(this.balade)
      .subscribe(
        (res: Balade[]) => {
          // Update the list of balades
          this.balades = res;

          // Inform the user
          this.success = 'Created successfully';

          // Reset the form
          f.reset();
        },
        (err) => this.error = err
      );
  }

这是错误：

TypeError: Cannot read property 'push' of null
    at t.project (main.6f2a73c37c9b189cf02f.js:1)
    at t._next (main.6f2a73c37c9b189cf02f.js:1)
    at t.next (main.6f2a73c37c9b189cf02f.js:1)
    at t._next (main.6f2a73c37c9b189cf02f.js:1)
    at t.next (main.6f2a73c37c9b189cf02f.js:1)
    at t._next (main.6f2a73c37c9b189cf02f.js:1)
    at t.next (main.6f2a73c37c9b189cf02f.js:1)
    at t.notifyNext (main.6f2a73c37c9b189cf02f.js:1)
    at t._next (main.6f2a73c37c9b189cf02f.js:1)
    at t.next (main.6f2a73c37c9b189cf02f.js:1)

Answer 1

尝试一下：

store(balade: Balade): Observable<Balade[]> {
  var ref = this; // Store the this into one variable and then use that variable to access a global scope
    return this.http.post(`${this.baseUrl}/store.php`, { data: balade })
     .pipe(map((res) => {
      ref.balades.push(res['data']);
      return this.balades;
    }),
    catchError(this.handleError));
}

编辑：

在使用中：

balades: Balade[] = [];

Answer 2

您没有使用箭头函数来定义store方法，因此this的作用域是该函数，而不是类。

  getBalades = (): void => {
    this.baladeService.getAll().subscribe(
      (res: Balade[]) => {
        this.balades = res;
      },
      (err) => {
        this.error = err;
      }
    );
  }

Answer 3

更改此

store(balade: Balade): Observable<Balade[]> {
    return this.http.post(`${this.baseUrl}/store.php`, { data: balade })
      .pipe(map((res) => {
        this.balades.push(res['data']);
        return this.balades;
      }),
      catchError(this.handleError));
  }

到

 store(balade: Balade): Observable<Balade[]> {
    return this.http.post(`${this.baseUrl}/store.php`, { data: balade })
      .pipe(map((res) => {
        this.balades = this.balades || []; //this will make your array empty if null
        this.balades.push(res['data']);
        return this.balades;
      }),
      catchError(this.handleError));
  }

this.balades在商店运行时为空。或者您可以尝试

constructor(private http: HttpClient) { }

到

constructor(private http: HttpClient) { getAll(); } // fill this.balades

Answer 4

def read_data(): # reading from file file = open("D:/Cs/Grad/Tests/airplane test/Reading/Positions/PlanePos.txt", "r") planepos = file.readline() file.close() file = open("D:/Cs/Grad/Tests/airplane test/Reading/Positions/AirportPosition.txt", "r") airportpos = file.readline() file.close() # ================================================================== # spliting and getting numbers #plane_X, plane_Y, plane_Z = map(float, planepos.strip('() \n').split(',')) #airport_X, airport_Y, airport_Z = map(float, airportpos.strip('() \n').split(',')) planepos=planepos.strip('() \n').split(',') airportpos=airportpos.strip('() \n').split(',') return planepos[0], planepos[1], planepos[2], airportpos[0], airportpos[1], airportpos[2]出了点问题，由于数组的push属性不起作用，它不能作为数组工作。您可以通过分配一个空数组来使其成为数组。

例如

balades

在balade.service.ts

 this.arrayName = this.arrayName || []; //assign an empty array

Answer 5

    let create = document.getElementById("create");
create.addEventListener("click", function(e) {
  let addTxt = document.getElementById("addTxt");
  let notes = localStorage.getItem("notes");
  if (notes == null) {
    notesObj = [];
  } else {
    notesObj = JSON.parse(notes);
  }
  notesObj.push(addTxt.value);
  localStorage.setItem("notes", JSON.stringify(notesObj));
  addTxt.value = "";
//   console.log(notesObj);
  showNotes();
});

TypeError：无法读取null的属性“ push”

5 个答案: