# CheckBox

The `CheckBox` control is a [`ContentControl`](https://docs.avaloniaui.net/docs/controls/contentcontrol) which allows user to check an option. It is usually used to display a boolean option where selection is either *checked* or *unchecked*. But it also supports three state mode where selection is either *checked*, *indeterminate* or *unchecked*.

## Common Properties

| Property       | Description                       |
| -------------- | --------------------------------- |
| `IsChecked`    | Is `CheckBox` checked             |
| `IsThreeState` | Is `CheckBox` in three state mode |

## Reference

[Checkbox](http://reference.avaloniaui.net/api/Avalonia.Controls/CheckBox/)

## Source code

[CheckBox.cs](https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Controls/CheckBox.cs)

## Examples

### Basic checkbox

```markup
<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaAppTemplate.MainWindow"
        Title="CheckBox sample">
    <StackPanel>
        <CheckBox>Not checked by default</CheckBox>
        <CheckBox IsChecked="True">Checked by default</CheckBox>
    </StackPanel>
</Window>
```

produces following output with **Windows 10**\\

![Basic checkbox](https://4025525846-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9CodmwWc6hOAzwuMGtm4%2Fuploads%2Fgit-blob-462c6a71a67e5bb4661a8fcb19dd012d54a8fdd8%2Fcheckbox_basic.png?alt=media)

### Three state checkbox

```markup
<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaAppTemplate.MainWindow"
        Title="CheckBox sample">
    <StackPanel>
        <CheckBox IsThreeState="True" IsChecked="False">Not checked by default</CheckBox>
        <CheckBox IsThreeState="True" IsChecked="True">Checked by default</CheckBox>
        <CheckBox IsThreeState="True" IsChecked="{x:Null}">Indeterminate by default</CheckBox>
    </StackPanel>
</Window>
```

produces following output with **Windows 10**\\

![Three state checkbox](https://4025525846-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9CodmwWc6hOAzwuMGtm4%2Fuploads%2Fgit-blob-75ef5c964f2573a1e78a3fc0bffdfad1a15545d2%2Fcheckbox_threestate.png?alt=media)