Angular，绑定输入类型Checkbox，默认勾选

Question

I am working on Angular 5 application with checkbox. I have data coming from database, followed by mapped to javaScript object. I am trying to configure 'Selected' value but unable to do so. In my result, I got all boxes checked which should be.

in following code, option: [] --> 'optionSelected' defined if is selected value by true or false,

produced schema as following;

Template

 <div *ngSwitchCase="'checkbox'"> <small>checkbox</small>
       <div *ngFor="let opt of question.options" >
            <label class="container-vertical"> {{opt.value}}
                <input type="checkbox" [formControlName]="question.key" [name]="opt.name" [value]="opt.key" [checked]="opt.optionSelected" /> 
                <span class="checkmark2"></span>
            </label>
       </div>      
 </div> 

also tried with ngModel as in my component, property 'value' holds id of selected key but still final result checked all boxes

<input type="checkbox" [formControlName]="question.key" [name]="opt.name" [value]="opt.key" [(ngModel)]="question.value" />

component

 else  if(questionElementType=="checkbox")
 {
   let _checkBox = new CheckBoxQuestion ({
     consultationId: questionsList[key].consultationId,
     questionId: questionsList[key].questionId,
     questionElementType: questionsList[key].questionElementType[0].title,           
     questionType: questionsList[key].questionType,
     title:questionsList[key].title,
     displayId: questionsList[key].displayId,
     key: questionsList[key].questionId,     
     value: questionsList[key].answer.length<=0? null : questionsList[key].answer[0].answerValue.toLowerCase(),
     label: questionsList[key].title, 
     order: 7,
     options: questionsList[key].answerOptions.map(function(item){
       return {"name": item.ReferenceKey, "key": item.preDefineAnswerOptionId, "value": item.text, "optionSelected": item.preDefineAnswerOptionId==questionsList[key].answer[0].answerValue? "true": "false"}
    }),
   });

     this.mappedQuestions.push(_checkBox);
 }

Answer 1

If you want the checkbox to be unchecked, its [value] binding must be falsy.

Both "true" and "false" are non empty strings, which means that they evaluate to true .

Convert "false" to false and it will work as expected.

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

@Component({
  selector: 'my-app',
  template: `
<input type="checkbox" [(ngModel)]="checkbox1" /> "true"
<input type="checkbox" [(ngModel)]="checkbox2" /> "false"
<input type="checkbox" [(ngModel)]="checkbox3" /> true
<input type="checkbox" [(ngModel)]="checkbox4" /> false
  `,
  styleUrls: [ './app.component.css' ]
})
export class AppComponent  {
  checkbox1 = 'true';
  checkbox2 = 'false';
  checkbox3 = true;
  checkbox4 =  false;
}

Live demo

Answer 2

You can use it

 <input type="checkbox" [(ngModel)]="active" [checked]="true" 
(change)="isAactiveChange($event)" >