如何防止 Angular 中的多个订阅调用？

Question

我有一个消息服务，用于在各种组件之间进行交互。当我点击Mine 按钮时，我只想触发一条消息。到目前为止，这有效。但是当我单击< 和> 按钮时，它会触发getMessage()，以便将值相加。但是当我点击Mine 时，我只想发送一个值。仅最后一个值。点击<和>时如何防止触发getMessage()？

当我点击<和>时，它会在卡片之间从1切换到10。当我点击Mine时，它应该只取我所在的卡片并将信息从该块发送到另一个组件。但相反，当我单击 < 或 > 时，getMessage() 被调用，它会将所有卡片加起来，直到我单击 Mine。我该如何防止呢？

遵循一些代码。我尽量保持紧凑：

消息服务.ts：

@Injectable({ providedIn: 'root' })
export class MessageService {
  private subject = new Subject<any>();

  sendMessage(message: string) {
    this.subject.next({ text: message });
  }

  getMessage(): Observable<any> {
    console.log('Get Message Message Service');
    return this.subject.asObservable();
  }

矿工卡组件：

  message: any;
  subscription: Subscription;

  constructor(private ref: ChangeDetectorRef, private emitTransactionService: EmitTransactionService,
              private messageService: MessageService) {
    this.subscription = this.messageService.getMessage().subscribe(message => {
      console.log('Constructor miner-card'); // gets called multiple times, depending on how often I click < and >. When I click 10 times on < or > it will call this subscription 10 times.
    });
  }

当我点击<和>时，这些函数被调用： 根据 minerCounter 的值，显示卡 1-10。

  precedingBlock() {
    this.minerCounter--;

    if (this.minerCounter < 1) {
      this.minerCounter = 10;
    }
  }

  nextBlock() {
    this.minerCounter++;

    if (this.minerCounter > 10) {
      this.minerCounter = 1;
    }
  }

带有<和>按钮的卡片的外观：

Mine 按钮：

Answer 1

您应该始终unsubscribengOnDestroy 中的订阅。

  message: any;
  subscription: Subscription;

  constructor(private ref: ChangeDetectorRef, private emitTransactionService: EmitTransactionService,
              private messageService: MessageService) {
    this.subscription = this.messageService.getMessage().subscribe(message => {
      console.log('Constructor miner-card'); // gets called multiple times, depending on how often I click < and >. When I click 10 times on < or > it will call this subscription 10 times.
    });
  }

ngOnDestroy() {
  this.subscription.unsubscribe();
}

Answer 2

在您的miner-card.component.ts 文件中使用take(1)。这只会从订阅中获取单个数据。

  message: any;
  subscription: Subscription;

  constructor(private ref: ChangeDetectorRef, private emitTransactionService: EmitTransactionService,
              private messageService: MessageService) {
    this.subscription = this.messageService.getMessage().pipe(take(1)).subscribe(message => {
      console.log('Constructor miner-card'); // gets called multiple times, depending on how often I click < and >. When I click 10 times on < or > it will call this subscription 10 times.
    });
  }

希望这会有所帮助！

Answer 3

检查您的订阅是否未定义。如果未定义，则仅订阅。

constructor(
private ref: ChangeDetectorRef,
private emitTransactionService: EmitTransactionService,
private messageService: MessageService
) {
if (!this.subscription) {
    this.subscription = this.messageService.getMessage().subscribe(message => {
      console.log('Constructor miner-card'); // gets called multiple times, depending on how often I click < and >. When I click 10 times on < or > it will call this subscription 10 times.
    });
  }
}