Pagination in Django ListView

from django.views.generic import ListView
from .models import Task

class TaskListView(ListView):
    model = Task
    template_name = 'tasks/task_list.html'
    context_object_name = 'tasks'
    paginate_by = 20  # objects per page
    ordering = ['-created_at']

{% for task in tasks %}
  <div>{{ task.title }}</div>
{% endfor %}

{% if is_paginated %}
<nav>
  {% if page_obj.has_previous %}
    <a href="?page={{ page_obj.previous_page_number }}">← Previous</a>
  {% endif %}

  <span>{{ page_obj.number }} / {{ page_obj.paginator.num_pages }}</span>

  {% if page_obj.has_next %}
    <a href="?page={{ page_obj.next_page_number }}">Next →</a>
  {% endif %}
</nav>
{% endif %}

<!-- Preserve GET parameters when navigating between pages -->
<a href="?{{ request.GET.urlencode }}&page={{ page_obj.next_page_number }}">Next</a>

from django.core.paginator import Paginator

def task_list(request):
    tasks = Task.objects.all().order_by('-created_at')
    paginator = Paginator(tasks, 20)
    page_number = request.GET.get('page', 1)
    page_obj = paginator.get_page(page_number)

    return render(request, 'tasks/list.html', {'page_obj': page_obj})