Angular 对用于属性绑定的模板参考变量的更改检测

Question

I'm playing around with template reference variables. And thought of using its value to set the disabled property on a button. ie disable a button unless the input field is non-empty. I expected the following code to work but the button stays disabled even after some value is entered in the input.

Why does Angular change detection not work in this case?

Is there another way to do achieve this using ONLY template reference variables?

The code is written in Angular 8 and node 12.16.2

<div class="form-group col-md-6">
    <input #hello type="text" class="form-control" id="01">
</div>
<div class="form-group col-md-6">
    <button class="btn btn-primary" [disabled]="hello.value.length === 0">Deactivate</button>
</div>

Answer 1

You can try ngForm combined with ngModel directive to achieve this,

<form #testForm="ngForm">
    <div class="form-group col-md-6">
        <input type="text" name="hello" ngModel class="form-control" id="01">
    </div>
    <div class="form-group col-md-6">
        <button class="btn btn-primary" [disabled]="testForm.value.hello.length === 0">
            Deactivate
        </button>
    </div>
</form>

{{testForm.value|json}}

Demo: https://stackblitz.com/edit/angular-ivy-xtdm4k?file=src/app/app.component.html

For more details, see this .