How to find the window state of float window in WPF DockingManager?

<Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="40"/>
    <RowDefinition Height="*"/>
  </Grid.RowDefinitions>
  <Button x:Name="_Statechanged" Width="150" Height="23" Content="Get FloatWindowstate" Click="FloatWindowState1" Grid.Row="0" />
  <syncfusion:DockingManager x:Name="Docking" UseDocumentContainer="True" Grid.Row="1" UseNativeFloatWindow="True">
    <ContentControl x:Name="Child1" syncfusion:DockingManager.Header="Content1" syncfusion:DockingManager.State="Float" syncfusion:DockingManager.CanFloatMaximize="True"/>
    <ContentControl x:Name="Child2" syncfusion:DockingManager.Header="Content2" syncfusion:DockingManager.State="Document" syncfusion:DockingManager.CanFloatMaximize="True"/>                            
  </syncfusion:DockingManager>
</Grid>

private void FloatWindowState1(object sender, RoutedEventArgs e)
{
  WindowState m = DockingManager.GetFloatWindowState(Child1);
  MessageBox.Show("Element window state is " + m.ToString());
            
}