Visual Studio/WPF > 컨트롤 > CheckBox > Indeterminate 속성 > IsThreeState를 True로 선택 가능

Windows 7 Pro (32bit)
Microsoft Visual Studio 2017 Community
Sublime Text 2

<Window x:Class="_170425_t1950_checkbox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        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"
        xmlns:local="clr-namespace:_170425_t1950_checkbox"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <CheckBox Content="CheckBox1" IsThreeState="True"></CheckBox>
    </Grid>
</Window>