# ClassesListSelector
## Introduction
**`Classes List Selector`** widget allows users to view a list of object classes and change it dynamically using widget methods. This widget can be used for visualizing and selecting classes in Supervisely.
[Read this tutorial in developer portal.](https://developer.supervisely.com/app-development/apps-with-gui/classes-list-selector)
## Function signature
```python
classes_list_selector = ClassesListSelector(
classes=obj_classes,
multiple=True,
empty_notification=None,
widget_id=None
)
```
{% tabs %}
{% tab title="Default with classes" %}
Default with classes
{% endtab %}
{% tab title="Default without classes" %}
Default without classes
{% endtab %}
{% endtabs %}
## Parameters
| Parameters | Type | Description |
| :------------------: | :-----------------------------------------: | :---------------------------------------------------------------------: |
| `classes` | `Union[List[ObjClass], ObjClassCollection]` | Supervisely object class collection or list of object classes |
| `multiple` | `bool` | Enable multiple classes selection |
| `empty_notification` | `NotificationBox` | Notification that will be displayed when there are no classes in widget |
| `widget_id` | `str` | ID of the widget |
| `allow_new_classes` | `bool` | Allow adding new classes dynamically |
### classes
List of `ObjClass` objects or Supervisely object class collection (`ObjClassCollection`).
**type:** `Union[List[ObjClass], ObjClassCollection]`
```python
classes_list_selector = ClassesListSelector(
classes=obj_classes
)
```
### multiple
If `True` then multiple classes can be selected. Otherwise, only one class can be selected.
**type:** `bool`
**default** `False`
```python
classes_list_selector = ClassesListSelector(
classes=obj_classes,
multiple=True
)
```
{% tabs %}
{% tab title="Multiple Enabled" %}
Multiple Enabled
{% endtab %}
{% tab title="Multiple disabled" %}
Multiple disabled
{% endtab %}
{% endtabs %}
### empty\_notification
Notification that will be displayed when there are no classes in widget
**type:** `NotificationBox`
**default** `None`
```python
notification_box = NotificationBox(title="No classes", description="Provide classes to the widget.")
classes_list_selector = ClassesListSelector(
multiple=True,
empty_notification=notification_box
)
```
### widget\_id
ID of the widget.
**type:** `str`
**default value:** `None`
### allow\_new\_classes
Allow adding new classes dynamically.
**type:** `bool`
**default value:** `False`
## Methods and attributes
| Attributes and Methods | Description |
| :----------------------: | --------------------------------------------- |
| `set()` | Set classes to widget. |
| `get_selected_classes()` | Return list of selected classes. |
| `select_all()` | Select all classes. |
| `deselect_all()` | Deselect all classes. |
| `select()` | Select classes by names. |
| `deselect()` | Deselect classes by names. |
| `set_multiple()` | Set multiple flag. |
| `get_all_classes()` | Return list of all classes. |
| `@selection_changed` | Callback triggers when selection is changed. |
| `@class_created` | Decorator to handle new class creation event. |
## Mini App Example
You can find this example in our Github repository:
[supervisely-ecosystem/ui-widgets-demos/media/010\_object\_classes\_list/src/main.py](https://github.com/supervisely-ecosystem/ui-widgets-demos/blob/master/media/010_object_classes_list/src/main.py)
### Import libraries
```python
import os
import supervisely as sly
from supervisely.app.widgets import (
Card,
Container,
ClassesListSelector,
NotificationBox,
Text,
)
from dotenv import load_dotenv
```
### Init API client
First, we load environment variables with credentials and init API for communicating with Supervisely Instance:
```python
load_dotenv("local.env")
load_dotenv(os.path.expanduser("~/supervisely.env"))
api = sly.Api()
```
### Create list of object classes
```python
cat_obj_class = sly.ObjClass("cat", sly.Rectangle)
dog_obj_class = sly.ObjClass("dog", sly.Rectangle)
horse_obj_class = sly.ObjClass("horse", sly.Rectangle)
sheep_obj_class = sly.ObjClass("sheep", sly.Rectangle)
cow_obj_class = sly.ObjClass("cow", sly.Rectangle)
elephant_obj_class = sly.ObjClass("elephant", sly.Rectangle)
bear_obj_class = sly.ObjClass("bear", sly.Rectangle)
zebra_obj_class = sly.ObjClass("zebra", sly.Rectangle)
obj_classes = [
cat_obj_class,
dog_obj_class,
horse_obj_class,
sheep_obj_class,
cow_obj_class,
elephant_obj_class,
bear_obj_class,
zebra_obj_class,
]
```
### Initialize `ClassesListSelector` widget with class creation enabled
```python
notification_box = NotificationBox(title="No classes", description="Provide classes to the widget.")
classes_list_selector = ClassesListSelector(
obj_classes, multiple=True, empty_notification=notification_box, allow_new_classes=True
)
selected_classes_cnt = Text(f"Selected classes: 0 / {len(obj_classes)}")
info_text = Text("You can create new classes using the Add new class button", status="info")
```
### Create app layout
Prepare a layout for app using `Card` widget with the `content` parameter and place widget that we've just created into the `Container` widget.
```python
container = Container(
widgets=[
info_text,
selected_classes_cnt,
classes_list_selector,
]
)
card = Card(
title="Classes List Selector",
content=container,
)
layout = card
```
### Create app using layout
Create an app object with layout parameter.
```python
app = sly.Application(layout=layout)
```
### Add functions to control widgets from python code
```python
# Update counters helper
def update_counters():
all_classes = classes_list_selector.get_all_classes()
selected = classes_list_selector.get_selected_classes()
selected_classes_cnt.set(f"Selected classes: {len(selected)} / {len(all_classes)}", "text")
@classes_list_selector.selection_changed
def selection_changed(classes):
update_counters()
@classes_list_selector.class_created
def on_class_created(new_class):
info_text.set(f"New class created: '{new_class.name}' ({new_class.geometry_type.name()})", "success")
update_counters()
```
