CheckBox, WPF

A CheckBox allows an option to be set, or unset. This control by default has 2 states: Checked and Unchecked—an Indeterminate state is also possible.

We use event handlers (CheckBox_Checked and Unchecked) to detect changes. IsChecked tells us the current state.

XAML example

We create a new WPF project and add a CheckBox control. In the XAML section, add the "Checked" attribute and allow Visual Studio to create the CheckBox_Checked event handler.

<Window x:Class="WpfApplication6.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <CheckBox
            Content="CheckBox"
            HorizontalAlignment="Left"
            Margin="10,10,0,0"
            VerticalAlignment="Top"
            Checked="CheckBox_Checked"
            Unchecked="CheckBox_Unchecked"/>
    </Grid>
</Window>

Code example

The CheckBox_Checked and CheckBox_Unchecked methods call a third method, Handle(), that deals with CheckBox changes. They pass the "sender" object cast to a CheckBox.

using System.Windows;
using System.Windows.Controls;

namespace WpfApplication6
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void CheckBox_Checked(object sender, RoutedEventArgs e)
        {
            Handle(sender as CheckBox);
        }

        private void CheckBox_Unchecked(object sender, RoutedEventArgs e)
        {
            Handle(sender as CheckBox);
        }

        void Handle(CheckBox checkBox)
        {
            // Use IsChecked.
            bool flag = checkBox.IsChecked.Value;

            // Assign Window Title.
            this.Title = "IsChecked = " + flag.ToString();
        }
    }
}

IsThreeState

The CheckBox optionally supports 3 states. Please add the IsThreeState attribute to the XAML. This third state is called the "indeterminate" state.

<Window x:Class="WpfApplication6.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <CheckBox
            Content="CheckBox"
            HorizontalAlignment="Left"
            Margin="10,10,0,0"
            VerticalAlignment="Top"
            Checked="CheckBox_Checked"
            Unchecked="CheckBox_Unchecked"
            Indeterminate="CheckBox_Indeterminate"
            IsThreeState="True"/>
    </Grid>
</Window>
using System.Windows;

namespace WpfApplication6
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void CheckBox_Checked(object sender, RoutedEventArgs e)
        {
            this.Title = "Checked";
        }

        private void CheckBox_Unchecked(object sender, RoutedEventArgs e)
        {
            this.Title = "Unchecked";
        }

        private void CheckBox_Indeterminate(object sender, RoutedEventArgs e)
        {
            this.Title = "Indeterminate";
        }
    }
}

Many CheckBox controls require only the Checked and Unchecked events. But the Indeterminate state is also available. CheckBox presents an option to the user.