Call to undefined function form_open()

In BaseController.php i am autoloading [b]form helper[/b].

Code:

protected $helpers = ["form"];

[b]Route:[/b]

Code:

$routes->get('admin/login', 'admin\LoginController::index');

[b]Controller:[/b]

Code:

public function index()
{
   
    echo view('admin/login');
}

[b]View:[/b]

Code:

<?php echo form_open('admin/dologin');?>
    <?= csrf_token() ?>
    <div class="input-group mb-3">
      <input type="email" class="form-control" name="email" placeholder="Email">
      <div class="input-group-append">
        <div class="input-group-text">
          <span class="fas fa-envelope"></span>
        </div>
      </div>
    </div>
    <div class="input-group mb-3">
      <input type="password" class="form-control" name="password" placeholder="Password">
      <div class="input-group-append">
        <div class="input-group-text">
          <span class="fas fa-lock"></span>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-4">
        <button type="submit" class="btn btn-primary btn-block">Sign In</button>
      </div>
      <!-- /.col -->
    </div>
  <?php echo form_close();?>

[b]How can i get rid of from this error?[/b]

Code:

Call to undefined function form_open()