Change the background color on ion-select based on the selected value

Question

I'm using Ionic 5.0 and I have an ion-select field. I need to change the background of the field based on the selected option.

I've tried several things. My current attempt in the code below is to insert [ngStyle]="SetBackground(item.id)" in the ion-select but that doesn't work. I've also tried [ngStyle]="SetBackground($event)". I've thought about somehow adding it to a (ionChange)="OnChange($event)" but couldn't figure out how to do that. It seems like I just need to use the item.id to change the background, but for the life of me I just can't figure it out.

Here's my HTML code. I hope this is enough to help me find an answer.

<ion-content>

  <div id="game-board">

    <ion-img class="map-img" src="../assets/img/map-a.png"></ion-img>

    <ion-select [(ngModel)]="selectedVal" class="square" interface="popover" [ngStyle]="SetBackground(item.id)">

      <ion-select-option *ngFor="let item of data" [value]="item.id" >

        {{ item.name }}

      </ion-select-option>

    </ion-select>

  </div>

</ion-content>

And my ts

import { Component } from '@angular/core';
import { Platform } from '@ionic/angular';

@Component({
  selector: 'app-home',
  templateUrl: 'home.page.html',
  styleUrls: ['home.page.scss'],
})
export class HomePage {
  data: { id: string; name: string; }[];

  constructor(private platform: Platform) {
    this.platform.ready().then(() => {
      this.data = [
        {
          id: "transparent", name: ""
        },
        {
          id: "green", name: "Forest"
        },
        {
          id: "red", name: "Village"
        },
        {
          id: "yellow", name: "Field"
        },
        {
          id: "blue", name: "Water"
        },
        {
          id: "purple", name: "Monster"
        },
      ]
    })
  }

  SetBackground(bg) {
    let newColor = {
      'background-color': bg.target.value,
    };
    return newColor
  }

The error I get...

HomePage.html:12 ERROR TypeError: Cannot read property 'id' of undefined
    at Object.eval [as updateDirectives] (HomePage.html:14)
    at Object.debugUpdateDirectives [as updateDirectives] (core.js:45259)
    at checkAndUpdateView (core.js:44271)
    at callViewAction (core.js:44637)
    at execComponentViewsAction (core.js:44565)
    at checkAndUpdateView (core.js:44278)
    at callViewAction (core.js:44637)
    at execEmbeddedViewsAction (core.js:44594)
    at checkAndUpdateView (core.js:44272)
    at callViewAction (core.js:44637)

Answer 1

<ion-select [(ngModel)]="selectedVal" class="square" interface="popover" [ngStyle]="SetBackground(item.id)">

  <ion-select-option *ngFor="let item of data" [value]="item.id" >

your SetBackground function is called before the loop. So there is no reference for item.id.

You can something like this.

html

<select [ngStyle]="styleObj" (change)="SetBackground($event)">

  <option *ngFor="let item of data"  value={{item.id}}>

    {{ item.name }}

  </option>

</select>

ts

 data = [
        {
          id: "transparent", name: ""
        },
        {
          id: "green", name: "Forest"
        },
        {
          id: "red", name: "Village"
        },
        {
          id: "yellow", name: "Field"
        },
        {
          id: "blue", name: "Water"
        },
        {
          id: "purple", name: "Monster"
        },
      ];

  styleObj = {};

  SetBackground(e) {
    this.styleObj = {
      'background-color': e.target.value,
    };
  }