Angular 排空阵列故障

Question

Hell, I have an e-commerce application in which I am trying to empty the shopping cart after payment is successful, no matter what I have tried the array will not empty. I have tried cartItems.length = 0, cartItems = [] as well as splice. I must be missing something. Code snippet below I will walk you through it.

This is my Model

import { Product } from './product';


export class CartItem {
    id: number;
    productId: number;
    productName: string;
    qty: number;
    price: number;
    size:string;
    imageUrl:string;

    constructor(id:number, size:string,  
     product:Product, qty= 1) {

        this.id = id;
        this.productId = product.id;
        this.price = product.price;
        this.size = size;
        this.productName = product.name;
        this.qty = qty;
        this.imageUrl = product.imageUrl;        
        
    }
    
}

This is my car service as you can see I remove and add to cart as well as get cart items, there is no problem here. The remove and add are button clicks on html

export class CartService {


  product: any;


 cartItem: CartItem[] = [];
    
  cartUrl = 'http://localhost:4000/cart';
  

  constructor(private http: HttpClient, private router: Router, 
  private route: ActivatedRoute) {
    
 }

   getCartItems(): Observable<CartItem[]> {
     return this.http.get<CartItem[]>(cartUrl).pipe(
      map((result: any[]) => {
        let cartItems: CartItem[] =[];
         

        for(let item of result) {
           
            cartItems.push( new CartItem(item.id, item.size, 
            item.product, item.imageUrl ));
            
       }
         
        return cartItems;
        
       })
     );

        
   }
 
  

   addProductToCart(product:Product):Observable<any>{
     return this.http.post(cartUrl, {product});
   }

   

   RemoveProductFromCart(id:number):Observable<void>{
     //this.cartItems.splice(index,1)
     alert("show deleted item");
     return this.http.delete<CartItem[]>(`${this.cartUrl}/${id}`)
     .pipe(catchError(_err => of (null))
      
     );
    }


    buttonClick() { 
      const currentUrl = this.router.url;
      this.router.navigateByUrl('/', {skipLocationChange: 
       true}).then(() => {
          this.router.navigate([currentUrl]);
      });
  
        //alert("Should Reload");
    } 
  

    addPurseToCart(product:Product):Observable<any>{
      return this.http.post(cartUrl, {product})


    }

    

    }

Here is the checkout component, I injected the cart component so I could call the the empty cart function which resides in the cart component. I did import the CartComponent. Check out is based on cart. When the cart is emptied so should checkout

@Component({
   
    providers:[CartComponent],   //injected CartComponent
    selector: 'app-checkout',
    templateUrl: './checkout.component.html',
    styleUrls: ['./checkout.component.scss']
  })


  export class CheckoutComponent implements OnInit {
   
   // @ViewChild(CartComponent)   // @ViewChild(CartItemComponent) cartitemComponent: CartItemComponent
 cartComponent: CartComponent
    
  @Input() product: CartItem;
  @Input() cartItem: CartItem;
   
     
  cartUrl = 'http://localhost:4000/cart';

  size;
  cartItems = [];

   cartTotal = 0;
   itemTotal = 0;  
   shipping = 8.00;
   estimatedTax = 0;
   myValue: any;
  
   

    constructor(private msg: MessengerService, private route: 
        ActivatedRoute,
        private router: Router,  private 
        cartService:CartService, 
        private productService: ProductService, private 
        comp:CartComponent) {}


    ngOnInit() {
       
        this.loadCartItems();

    }
   
    
   
       }

       loadCartItems(){

        this.cartService.getCartItems().subscribe((items: 
        CartItem[]) => {
        this.cartItems = items;
        this.calcCartTotal();
         this.calNumberOfItems();
       })
      }

      calcCartTotal() {
      
       this.cartTotal = 0;
         this.cartItems.forEach(item => {
           this.cartTotal += (item.qty * item.price); 
           
         })

         this.cartTotal +=  this.shipping;
         this.myValue = this.cartTotal
         render(
          {
           id:"#paypal-button-container",
           currency: "USD",
           value: this.myValue,

           onApprove: (details) =>{
               alert("Transaction Suceessfull")
               console.log(this.myValue);
               this.comp.handleEmptyCart();
              
               
           }

           
            
          } 
       );
       }
      
      
      calNumberOfItems(){
        console.log("Trying to get tolal items")
        this.itemTotal = 0;
        this.cartItems.forEach(item => {
        this.itemTotal += item.qty;
        })
       
       }

          
  }

cart component

  export class CartComponent implements OnInit {
     
     
      @Input() product: CartItem;
      @Input() cartItem: CartItem;
      
     //items: CartItem [] =[];
    
      cartUrl = 'http://localhost:4000/cart';
    
      val;
      size;
     cartItems = [];
      
    
      
       
      cartTotal = 0
      itemTotal = 0
    
      constructor(private msg: MessengerService, private 
        cartService:CartService, private productService: 
        ProductService, private formBuilder:FormBuilder, private 
       _data:AppserviceService, private router:Router) { }
     
      
     
    
      ngOnInit(): void {
         
         this.handleSubscription();
         this.loadCartItems();
    
    
      }
    
      handleSubscription(){
    
        this.msg.getMsg().subscribe((product: Product) => {   
        })
    
       }
    
    
       loadCartItems(){
    
         this.cartService.getCartItems().subscribe((items: 
         CartItem[]) => {
         this.cartItems = items;
         console.log("what is in cartItems" + this.cartItems)
         console.log("What does this property hold" + 
         this.cartItem)
         this.calcCartTotal();
         this.calNumberOfItems();
        })
       }
    
    
    
    calcCartTotal() {
     this.cartTotal = 0
     this.cartItems.forEach(item => {
        this.cartTotal += (item.qty * item.price)  
      })
    
    }
    
    calNumberOfItems(){
     console.log("Trying to get tolal items")
     this.itemTotal = 0
     this.cartItems.forEach(item => {
       this.itemTotal += item.qty
     })
    
    }
    
      handleEmptyCart(){
     
        alert("Hit Empty Cart");
        
        /*here I get the cart items to see what is in the array 
         and try to empty, it does show tow objects in the 
         array*/

        this.cartService.getCartItems().subscribe((items: 
          CartItem[]) => {
          this.cartItems = items;
          this.cartItems.length=0
           // this.cartItems = [];
          console.log("what is in cartItems"  + this.cartItems)
         
    
    })
    
    
      }
     
     
    
    }

I have used different approaches trying to empty the cart nothing works. It makes me think I'm stepping on something or somehow creating events calling the loadCartItems to many times not sure but according to my research one of these approaches should work. If someone can please help me out I'm stuck. I would greatly appreciate it.

Answer 1

Short answer: run change detection ChangeDetectorRef.detectChanges()

Long answer: You need to understand how angular works. Lets assume simple example:

<div id="val">{{val}}</div><button (click)="val++">Increase<div>

So when u click button variable changes, but who changes actual #val div content? Answer is that Angular uses zone.js to patch/change a lot of functions to run Angular change detection after most of JS events (you can control type of this events to include/exclude some of them). Also Promise is patched same way, thats why after some Promise is resolve change detection is run.

However, here you run some render method with onApprove callback which is probably some 3rd party library (?) and zone.js is not aware of it ( https://angular.io/guide/zone#ngzone-run-and-runoutsideofangular ). And though running detectChanges gonna help u, u better re-write your code, so onApprove is always in Angular zone and u never gonna face similar bugs in future when using this method.