# ClassesListPreview

## Introduction

**`Classes List Preview`** widget just displays a list of classes. It can be used to display classes that were selected by the user in the [Classes List Selector](https://developer.supervisely.com/app-development/apps-with-gui/classes-list-selector) widget for example.

## Function signature

```python
classes_list_preview = ClassesListPreview(
    classes=obj_classes,
    max_height="128px",
    empty_text = None,
    show_shape_title=True,
    show_shape_icon=True,
    widget_id = None,
    )
```

![default](https://github.com/supervisely-ecosystem/ui-widgets-demos/assets/48913536/6e287a14-c34c-423e-87e0-a00d3f8b9267)

## Parameters

|     Parameters     |                     Type                    |                           Description                           |
| :----------------: | :-----------------------------------------: | :-------------------------------------------------------------: |
|      `classes`     | `Union[List[ObjClass], ObjClassCollection]` |  Supervisely object class collection or list of object classes  |
|    `max_height`    |                    `bool`                   |                     Max height of the widget                    |
|    `empty_text`    |                    `str`                    | Text that will be displayed when there are no classes in widget |
| `show_shape_title` |                    `bool`                   |       If `True` show name of the shape next to class name       |
|  `show_shape_icon` |                    `bool`                   |         If `True` show icon of the shape near class name        |
|     `widget_id`    |                    `str`                    |                         ID of the widget                        |

### classes

List of `ObjClass` objects or Supervisely object class collection (`ObjClassCollection`).

**type:** `Union[List[ObjClass], ObjClassCollection]`

```python
classes_list_preview = ClassesListPreview(
    classes=obj_classes
)
```

### max\_height

Set the maximum height of the widget in pixels. If the content exceeds the maximum height, the scroll bar will appear.

**type:** `str`

**default** `"128px"`

```python
classes_list_preview = ClassesListPreview(
    classes=obj_classes,
    max_height="100px"
)
```

### empty\_text

Text that will be displayed when there are no classes in widget

**type:** `str`

**default** `None`

```python
empty_text = "No classes to preview"
classes_list_preview = ClassesListPreview(
    classes=[],
    empty_text=empty_text,
)
```

![empty-text](https://github.com/supervisely-ecosystem/ui-widgets-demos/assets/48913536/ca229395-0c19-4615-9f4c-8396c750c3f5)

### show\_shape\_title

If `True` show name of the shape next to class name.

**type:** `bool`

**default** `True`

```python
empty_text = "No classes to preview"
classes_list_preview = ClassesListPreview(
    classes=[],
    empty_text=empty_text,
)
```

![disable-shape-text](https://github.com/supervisely-ecosystem/ui-widgets-demos/assets/48913536/5a92c443-98cb-4f58-9033-63545a75fc12)

### show\_shape\_icon

If `True` show icon of the shape near class name.

**type:** `bool`

**default** `True`

```python
empty_text = "No classes to preview"
classes_list_preview = ClassesListPreview(
    classes=[],
    empty_text=empty_text,
)
```

![disable-shape-icon](https://github.com/supervisely-ecosystem/ui-widgets-demos/assets/48913536/bcbb5f4a-6d07-4b72-8ae0-a08e8123cfab)

### widget\_id

ID of the widget.

**type:** `str`

**default value:** `None`

## Methods and attributes

| Attributes and Methods | Description                                                                 |
| :--------------------: | --------------------------------------------------------------------------- |
|         `set()`        | Set classes to widget and determine wheter to display shape icon and title. |
|         `get()`        | Return list of classes.                                                     |

## Mini App Example

In this example we will create a mini app with `ClassesListPreview` widget. We will create a `ClassesListSelector` widget and display selected classes with `ClassesListPreview` widget.

You can find this example in our Github repository:

[supervisely-ecosystem/ui-widgets-demos/media/017\_classes\_list\_preview/src/main.py](https://github.com/supervisely-ecosystem/ui-widgets-demos/blob/master/media/017_classes_list_preview/src/main.py)

### Import libraries

```python
import os
import supervisely as sly
from supervisely.app.widgets import (
    Card,
    Container,
    ClassesListPreview,
    ClassesListSelector,
    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 and init `ClassesListSelector` widget

```python
cat_obj_class = sly.ObjClass("cat", sly.Rectangle)
dog_obj_class = sly.ObjClass("dog", sly.Polygon)
horse_obj_class = sly.ObjClass("horse", sly.Bitmap)
cow_obj_class = sly.ObjClass("cow", sly.Polyline)
zebra_obj_class = sly.ObjClass("zebra", sly.Point)
obj_classes = [
    cat_obj_class,
    dog_obj_class,
    horse_obj_class,
    cow_obj_class,
    zebra_obj_class,
]

classes_list_selector = ClassesListSelector(obj_classes, multiple=True)
```

### Initialize `ClassesListPreview` widget and `Text` widget for displaying number of selected classes

```python
classes_list_preview = ClassesListPreview()
preview_text = Text(f"Selected Classes: 0 / {len(obj_classes)}", "text")
preview_container = Container([preview_text, classes_list_preview])
```

### Create app layout

Prepare a layout for app using `Card` widget with the `content` parameter and place widgets that we've previously created into the `Container` widget.

```python
container = Container(widgets=[classes_list_selector, preview_container])

card = Card(
    title="Classes List Preview",
    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
@classes_list_selector.selection_changed
def on_selection_changed(selected_classes):
    preview_text.set(f"Selected Classes: {len(selected_classes)} / {len(obj_classes)}", "text")
    classes_list_preview.set(selected_classes)
```

![mini-app-min](https://github.com/supervisely-ecosystem/ui-widgets-demos/assets/48913536/568a4185-91b0-41fe-959b-0e65f90aceae)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://developer.supervisely.com/app-development/widgets/media/classeslistpreview.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.