*ngIf 的订阅值未更新

Question

这是我正在尝试做的事情的基本想法..！

我有一个导航栏，它对我的应用程序中的所有模块都是全局的。但是当我转到特定组件时，我想从我的导航栏中隐藏搜索栏。为此，我使用了创建全局变量并订阅它的方法（从导航栏订阅）

location.service.ts 是我的全局变量服务

import { Injectable } from '@angular/core';
import { Observable ,of as observableOf} from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class LocationService {
  private createnewproject: boolean = false;
  constructor() { }

public getcurrentlocation(): Observable<boolean>
{
  return  observableOf( this.createnewproject);
}

public setcurrentlocation(status:boolean)
{
  this.createnewproject = status ;
}

public checkvalue():boolean
{
  return this.createnewproject;
}

}

//createnewproject 最初是 false，一旦进入特定模块，我会将其设置为 true

这是我的导航栏 class 我也是这样订阅的

import { Component, OnInit } from '@angular/core';
import { ConstantsService } from '../common/services/constants.service';
import { LocationService} from '../common/services/location.service';
import { observable } from 'rxjs';

@Component({
  selector: 'app-ibrainmart-header',
  templateUrl: './ibrainmart-header.component.html',
  styleUrls: ['./ibrainmart-header.component.css']
})
export class IbrainmartHeaderComponent implements OnInit {
  oncreateproject: boolean;
  constructor( private projectloaction: LocationService) { }

  ngOnInit()
  {


    const oncreate = this.projectloaction.getcurrentlocation().subscribe(observable => { this.oncreateproject = observable;});

  }

}

这就是我计划使用 *ngIf

从代码中隐藏搜索栏的方式

 <div class="row" *ngIf = "!oncreateproject">
      <div class="col-md-12">
          <nav class="navbar navbar-expand-lg navbar-dark bg-primary">
                  <div class="input-group mb-3">
                  <input type="text" class="form-control"  placeholder="Search anything ..!" aria-label="Searchbar" aria-describedby="">
                      <div class="input-group-append">
                      <button class="btn btn-outline-light" type="button" id="btnsearch" ><i class="fa fa-search"></i>{{oncreateproject}}</button>
                      </div>


                  </div>
          </nav>
      </div>
  </div>

这就是我在到达特定页面后将全局变量设置为 true 的方式

import { Component, OnInit } from '@angular/core';
import { ConstantsService } from 'src/app/common/services/constants.service';
import { LocationService } from 'src/app/common/services/location.service';

@Component({
  selector: 'app-createnewproject',
  templateUrl: './createnewproject.component.html',
  styleUrls: ['./createnewproject.component.css']
})
export class CreatenewprojectComponent implements OnInit {

  createnewproject: boolean;

  constructor( private oncreateproject: LocationService) {

   this.oncreateproject.setcurrentlocation(true);
   console.log('Globle Value:' + this.oncreateproject.checkvalue());
   }

  ngOnInit()
  {

  }


}

但是当我转到此页面时，全局值正在更新，但 Serach 栏没有隐藏，有人可以帮我找到我做错的地方吗..？

Answer 1

你需要使用 rxjs subject of 函数只是创建一个可观察的值的基础，但不会将任何更改同步到属性这就是为什么我认为最好使用 Subject

import { Injectable } from '@angular/core';
import { Observable ,Subject , from} from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class LocationService {
  private createnewproject: Subject<boolean>= new Subject();
  constructor() { }


public getcurrentlocation(): Observable<boolean>
{
  return  from(this.createnewproject);
}

public setcurrentlocation(status:boolean)
{
  this.createnewproject.next(status);
}


}

IbrainmartHeaderComponent

export class IbrainmartHeaderComponent implements OnInit {

  // set initial value in case you want to see the search bar by default 
  oncreateproject: boolean = true;

  constructor( private projectloaction: LocationService) { }

  ngOnInit()
  {
    this.projectloaction.getcurrentlocation().subscribe(state => { 
      this.oncreateproject = state;
    });

  }

}

subjects

Answer 2

我会使用 BehaviorSubject 以便它保存一个初始值并且可以在视图中使用异步以便它解析该值。

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { BehaviorSubject } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class LocationService {
  private searchBarVisibility$ = new BehaviorSubject(true);
  constructor() { }

  public getcurrentlocation(): Observable<boolean> {
    return from(this.searchBarVisibility$);
  }

  public setcurrentlocation(status: boolean) {
    this.searchBarVisibility$.next(status);
  }

}

然后隐藏搜索栏

 <div class="row" *ngIf = "oncreateproject | async">
      <div class="col-md-12">
          <nav class="navbar navbar-expand-lg navbar-dark bg-primary">
                  <div class="input-group mb-3">
                  <input type="text" class="form-control"  placeholder="Search anything ..!" aria-label="Searchbar" aria-describedby="">
                      <div class="input-group-append">
                      <button class="btn btn-outline-light" type="button" id="btnsearch" ><i class="fa fa-search"></i>{{oncreateproject | async}}</button>
                      </div>
                  </div>
          </nav>
      </div>
  </div>

IbrainmartheaderComponent

import { Component, OnInit } from '@angular/core';
// import { ConstantsService } from '../constants.service';
import { LocationService} from '../location.service';
import { Observable } from 'rxjs';

@Component({
  selector: 'app-ibrainmart-header',
  templateUrl: './ibrainmart-header.component.html',
  styleUrls: ['./ibrainmart-header.component.css']
})
export class IbrainmartheaderComponent implements OnInit {
  oncreateproject: Observable<boolean>;
  constructor( private projectlocation: LocationService) { }

  ngOnInit()
  {
    this.oncreateproject = this.projectlocation.getcurrentlocation();
  }

}

创建新项目组件

import { Component, OnInit } from '@angular/core';
// import { ConstantsService } from 'src/app/common/services/constants.service';
import { LocationService } from '../location.service';

@Component({
  selector: 'app-createnewproject',
  templateUrl: './createnew-project.component.html',
  styleUrls: ['./createnew-project.component.css']
})
export class CreatenewprojectComponent {

  createnewproject: boolean;

  constructor(private projectlocation: LocationService) {
    this.projectlocation.getcurrentlocation().subscribe(value =>
          console.log('Globle Value:' + value)
    );
    this.projectlocation.setcurrentlocation(true);
  }

}

*ngIf 的订阅值未更新

Subscribe Value of *ngIf is not Updating

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angular