Question

嗨，我正在尝试编写* ngIf语句，该语句将通用字符串作为输入，这将依次返回true / false 例如

下面是示例组件html和ts文件。

   <div>
      <p *ngIf='hideExpression'>
        This will be visible only if employee member is employee.
      </p>
   </div>

users.component.ts

import { Component, OnInit } from '@angular/core';

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

  hideExpression = '';
  isEmployee = false;
  constructor() { }

  ngOnInit() {
    //Note:  I am going to fetch this expression from Database which is stored in string form
    this.hideExpression = 'isEmployee === true';
  }
}

我的成员变量hideExpression包含一个有效的字符串表达式，该表达式将返回true或false。如何使用此hideExperssion作为*ngIf的参数

Answer 1

更改为entry/x:=master.read()

this.hideExpression = this.isEmployee === true;

更新

如果要从数据库中获取hideExpression，则需要创建服务并像这样从DB中获取数据

ngOnInit() {
    this.hideExpression = this.isEmployee === true;
}

Answer 2

您不能将表达式放在字符串中使用方法

<div>
      <p *ngIf='isEmployee'>
        This will be visible only if employee member is employee.
      </p>
   </div>



import { Component, OnInit } from '@angular/core';

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


  isEmployee = false;
  constructor() { }
       hideExpression();
  ngOnInit() {

  }
   private hideExpression(){
     return !this.isEmployee;
   }
}

* ngIf具有评估布尔值的通用字符串表达式

2 个答案: