要在Angular的BehaviorSubject中获取从http调用中获取的数据，可以执行以下步骤：

1. 创建一个名为data.service.ts的服务文件，并导入所需的Angular模块和操作符：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { BehaviorSubject } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  private dataSubject = new BehaviorSubject(null);
  data$ = this.dataSubject.asObservable();

  constructor(private http: HttpClient) { }
}

2. 在服务文件中，创建一个方法来执行http调用并将数据发送到BehaviorSubject：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { BehaviorSubject } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  private dataSubject = new BehaviorSubject(null);
  data$ = this.dataSubject.asObservable();

  constructor(private http: HttpClient) { }

  fetchData() {
    this.http.get('your-api-url')
      .subscribe(data => {
        this.dataSubject.next(data);
      });
  }
}

3. 在组件中注入数据服务，并订阅data$ Observable以获取数据更新：

import { Component, OnInit } from '@angular/core';
import { DataService } from 'data.service';

@Component({
  selector: 'app-your-component',
  templateUrl: './your-component.component.html',
  styleUrls: ['./your-component.component.css']
})
export class YourComponent implements OnInit {
  data: any;

  constructor(private dataService: DataService) { }

  ngOnInit() {
    this.dataService.data$.subscribe(data => {
      this.data = data;
    });
    this.dataService.fetchData();
  }
}

这样，当组件初始化时，它将订阅data$ Observable，并在数据服务的fetchData方法中执行http调用。一旦数据从http调用中获取并发送到BehaviorSubject，组件将接收到更新的数据并进行相应的操作。