Checkbox angular material checked by default

Question

I am trying to use an Angular Material checkbox, and set it by default as checked, but it is displayed as non-checked, what is wrong?

<mat-checkbox class = "example-margin" [(ngModel)] = obj.impresora> 
     <label>Printer</label> 
</mat-checkbox>

obj.impresora property is boolean

Answer 1

You can either set with ngModel either with [checked] attribute. ngModel binded property should be set to 'true':

1.

  <mat-checkbox class = "example-margin" [(ngModel)] = "myModel"> 
    <label>Printer </label> 
  </mat-checkbox>

2.

<mat-checkbox [checked]= "myModel" class = "example-margin" > 
    <label>Printer </label> 
</mat-checkbox>

3.

<mat-checkbox [ngModel]="myModel" class="example-margin">
    <label>Printer </label> 
</mat-checkbox>

DEMO

Answer 2

this works for me in Angular 7

// in component.ts
checked: boolean = true;

changeValue(value) {
    this.checked = !value;
}

// in component.html
<mat-checkbox value="checked" (click)="changeValue(checked)" color="primary">
   some Label
</mat-checkbox>

I hope help someone ... greetings. let me know if someone have some easiest

Answer 3

The chosen answer does work however I wanted to make a comment that having 'ngModel' on the html tag causes the checkbox checked to not be set to true.

This occurs when you are trying to do bind using the checked property. i.e.

<mat-checkbox [checked]='var' ngModel name='some_name'></mat-checkbox>

And then inside your app.component.ts file

var = true;

will not work.

TLDR: Remove ngModel if you are setting the checked through the [checked] property

    <mat-checkbox [checked]='var' name='some_name'></mat-checkbox>

Answer 4

There are several ways you can achieve this based on the approach you take. For reactive approach, you can pass the default value to the constructor of the FormControl(import from @angular/forms)

this.randomForm = new FormGroup({
      'amateur': new FormControl(false),
});

Instead of true or false value, yes you can send variable name as well like FormControl(this.booleanVariable)

In template driven approach you can use 1 way binding [ngModel]="this.booleanVariable" or 2 way binding [(ngModel)]="this.booleanVariable" like this

<mat-checkbox
     name="controlName"
     [(ngModel)]="booleanVariable">
     {{col.title}}
</mat-checkbox>

You can also use the checked directive provided by angular material and bind in similar manner