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How to use a typescript enum value in an Angular2 ngSwitch statement

The Typescript enum seems a natural match with Angular2's ngSwitch directive. But when I try to use an enum in my component's template, I get "Cannot read property 'xxx' of undefined in ...". How can I use enum values in my component template?

Please note that this is different from how to create html select options based upon ALL of the values of an enum (ngFor). This question is about ngSwitch based upon a particular value of an enum. Although the same approach of creating an class-internal reference to the enum appears.

over 4 years ago · Santiago Trujillo

3 Respostas

Responde à pergunta

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This's simple and works like a charm :) just declare your enum like this and you can use it on HTML template

  statusEnum: typeof StatusEnum = StatusEnum;

over 4 years ago · Santiago Trujillo Relatório

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You can create a custom decorator to add to your component to make it aware of enums.

myenum.enum.ts:

export enum MyEnum {
    FirstValue,
    SecondValue
}

myenumaware.decorator.ts

import { MyEnum } from './myenum.enum';

export function MyEnumAware(constructor: Function) {
    constructor.prototype.MyEnum = MyEnum;
}

enum-aware.component.ts

import { Component } from '@angular2/core';
import { MyEnum } from './myenum.enum';
import { MyEnumAware } from './myenumaware.decorator';

@Component({
  selector: 'enum-aware',
  template: `
    <div [ngSwitch]="myEnumValue">
      <div *ngSwitchCase="MyEnum.FirstValue">
        First Value
      </div>
      <div *ngSwitchCase="MyEnum.SecondValue">
        Second Value
      </div>
    </div>
    <button (click)="toggleValue()">Toggle Value</button>
  `,
})
@MyEnumAware // <---------------!!!
export default class EnumAwareComponent {
  myEnumValue: MyEnum = MyEnum.FirstValue;

  toggleValue() {
    this.myEnumValue = this.myEnumValue === MyEnum.FirstValue
        ? MyEnum.SecondValue : MyEnum.FirstValue;
  }
}

over 4 years ago · Santiago Trujillo Relatório

Responde à pergunta

Encontrar trabalhos remotos

Accepted Answer · 2022-05-18T13:44:15.469Z

You can create a reference to the enum in your component class (I just changed the initial character to be lower-case) and then use that reference from the template (plunker):

import {Component} from 'angular2/core';

enum CellType {Text, Placeholder}
class Cell {
  constructor(public text: string, public type: CellType) {}
}
@Component({
  selector: 'my-app',
  template: `
    <div [ngSwitch]="cell.type">
      <div *ngSwitchCase="cellType.Text">
        {{cell.text}}
      </div>
      <div *ngSwitchCase="cellType.Placeholder">
        Placeholder
      </div>
    </div>
    <button (click)="setType(cellType.Text)">Text</button>
    <button (click)="setType(cellType.Placeholder)">Placeholder</button>
  `,
})
export default class AppComponent {

  // Store a reference to the enum
  cellType = CellType;
  public cell: Cell;

  constructor() {
    this.cell = new Cell("Hello", CellType.Text)
  }

  setType(type: CellType) {
    this.cell.type = type;
  }
}

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