Typescript Angular 外部订阅值 Null

欢迎使用StackOverflow.您看到undefined的原因是您混合了同步和异步代码，这通常会导致问题.只要把console.log移到subscribe里面就可以了.

// Asynchronous code - takes some time to finalize
this.entityServiceHandler.saveEntityWithCondition(entity).subscribe(data => {
  this.result = data;
  console.log(this.resul) // This'll be shown
});

// Synchronous code - happens just after calling previous, doesn't wait for it
// to finish. This means, result is undefined
console.log(this.result);

EDIT: 我冒昧地简化了您的代码.你在做很多不必要的事情，比如只有一个观察点就有forkJoin件.或者将订阅推送到一个数组，可能会在以后关闭它，但当您稍微引用代码时就不需要了.

import { filter, switchMap, catchError, EMPTY } from 'rxjs';

public saveEntityWithCondition(entity): Observable<Entity> {
  // No need to forkJoin, just call the function and pipe it
  return this.entityService.isConditionTrue(entity.property).pipe(
    // This makes sure that conditionTrue is true indeed
    filter(conditionTrue => conditionTrue),
    // Then use switchMap to call the entity service and perform save
    switchMap(() => this.entityService.save(entity)),
    // And use catchError to handle possible issues
    catchError(error => {
      // handle error in some way - i.e. log it or something;
      return EMPTY; 
    })
  );

}

您不再需要subject，因为您将直接返回Observable<Entity>.

您也不需要将Subscription推入数组，因为多亏了您正在使用的HttpClient和包含的switchMap操作符，当save结束时，它将自动处理unsubcribe.