Select based on enum in Angular2

问题:

I have this enum (I'm using TypeScript) :

export enum CountryCodeEnum {
    France = 1,
    Belgium = 2
}

I would like to build a select in my form, with for each option the enum integer value as value, and the enum text as label, like this :

<select>
     <option value="1">France</option>
     <option value="2">Belgium</option>
</select>

How can I do this ?

回答1:

update

instead of pipes: [KeysPipe]

use

@NgModule({
  declarations: [KeysPipe],
  exports: [KeysPipe],
}
export class SharedModule{}

@NgModule({
  ...
  imports: [SharedModule],
})

original

Using the keys pipe from https://stackoverflow.com/a/35536052/217408

I had to modify the pipe a bit to make it work properly with enums (see also How does one get the names of TypeScript enum entries?)

@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform {
  transform(value, args:string[]) : any {
    let keys = [];
    for (var enumMember in value) {
      if (!isNaN(parseInt(enumMember, 10))) {
        keys.push({key: enumMember, value: value[enumMember]});
        // Uncomment if you want log
        // console.log("enum member: ", value[enumMember]);
      } 
    }
    return keys;
  }
}

@Component({ ...
  pipes: [KeysPipe],
  template: `
  <select>
     <option *ngFor="let item of countries | keys" [value]="item.key">{{item.value}}</option>
  </select>
`
})
class MyComponent {
  countries = CountryCodeEnum;
}

Plunker

See also How to use *ngFor with Object?

回答2:

One more solution if you don't want to create a new pipe. You could also extract keys into helper property and use it:

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <select>
        <option *ngFor="let key of keys" [value]="key" [label]="countries[key]"></option>
      </select>
    </div>
  `,
  directives: []
})
export class App {

  countries = CountryCodeEnum

  constructor() {
    this.keys = Object.keys(this.countries).filter(Number)
  }
}

Demo: http://plnkr.co/edit/CMFt6Zl7lLYgnHoKKa4E?p=preview

回答3:

Here is a very straightforward way for Angular2 v2.0.0. For completeness sake, I have included an example of setting a default value of the country select via reactive forms.

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <select id="country" formControlName="country">
        <option *ngFor="let key of keys" [value]="key">{{countries[key]}}</option>
      </select>
    </div>
  `,
  directives: []
})
export class App {
  keys: any[];
  countries = CountryCodeEnum;

  constructor(private fb: FormBuilder) {
    this.keys = Object.keys(this.countries).filter(Number);
    this.country = CountryCodeEnum.Belgium; //Default the value
  }
}

回答4:

Another similar solution, that does not omit "0" (like "Unset"). Using filter(Number) IMHO is not a good approach.

@Component({
  selector: 'my-app',
  providers: [],
  template: `
  <select>
    <option *ngFor="let key of keys" [value]="key" [label]="countries[key]"></option>
  </select>`,
  directives: []
})

export class App {
  countries = CountryCodeEnum;

  constructor() {
    this.keys = Object.keys(this.countries).filter(f => !isNaN(Number(f)));
  }
}

// ** NOTE: This enum contains 0 index **
export enum CountryCodeEnum {
   Unset = 0,
   US = 1,
   EU = 2
}

回答5:

I've preferred to have a simple utility function shared across my Angular App, to convert the enum into a standard array to build selects:

export function enumSelector(definition) {
  return Object.keys(definition)
    .map(key => ({ value: definition[key], title: key }));
}

to fill a variable in the Component with:

public countries = enumSelector(CountryCodeEnum);

and then fill my Material Select as my old array based ones:

<md-select placeholder="Country" [(ngModel)]="country" name="country">
  <md-option *ngFor="let c of countries" [value]="c.value">
    {{ c.title }}
  </md-option>
</md-select>

Thanks for this thread!

回答6:

With string enums you can try this.

My string enum has the following definition:

    enum StatusEnum {
        Published = <any> 'published',
        Draft = <any> 'draft'
    }

and translates to js in the following way:

   {
       Published: "published", 
       published: "Published", 
       Draft: "draft", 
       draft: "Draft"
   }

I have a few of these in my project so created small helper function in a shared service lib:

   @Injectable()
   export class UtilsService {
       stringEnumToKeyValue(stringEnum) {
           const keyValue = [];
           const keys = Object.keys(stringEnum).filter((value, index) => {
               return !(index % 2);
           });

           for (const k of keys) {
               keyValue.push({key: k, value: stringEnum[k]});
           }

           return keyValue;
       }
   }

Init in your component constructor and Bind it to your template like this:

In component:

    statusSelect;

    constructor(private utils: UtilsService) {
        this.statusSelect = this.utils.stringEnumToKeyValue(StatusEnum);
    }

In template:

    <option *ngFor="let status of statusSelect" [value]="status.value">
        {{status.key}}
    </option>

Don't forget to add the UtilsService to the provider array in your app.module.ts so you can easily inject it in different components.

I'm a typescript newbie so please correct me if I'm wrong or if there are better solutions.

回答7:

Another spin off of this answer, but this actually maps the values as numbers, instead of converting them to strings which is a bug. It also works with 0 based enums

@Component({
  selector: 'my-app',
  providers: [],
  template: `
  <select>
<option *ngFor="let key of keys" [value]="key" [label]="countries[key]"></option>
  </select>`,
  directives: []
})

export class App {
  countries = CountryCodeEnum;

  constructor() {
    this.keys = Object.keys(this.countries)
                      .filter(f => !isNaN(Number(f)))
                      .map(k => parseInt(k));;
  }
}

回答8:

As of Angular 6.1 and above you can use the built-in KeyValuePipe like below (pasted from angular.io docs).

I'm assuming that an enum contains human friendly readable strings of course :)

@Component({
  selector: 'keyvalue-pipe',
  template: `<span>
    <p>Object</p>
    <div *ngFor="let item of object | keyvalue">
      {{item.key}}:{{item.value}}
    </div>
    <p>Map</p>
    <div *ngFor="let item of map | keyvalue">
      {{item.key}}:{{item.value}}
    </div>
  </span>`
})
export class KeyValuePipeComponent {
  object: {[key: number]: string} = {2: 'foo', 1: 'bar'};
  map = new Map([[2, 'foo'], [1, 'bar']]);
}