[FlagsAttribute]
public enum SelectionModes

public void SetSelectionModeExample()
{
    Project.UndoContext.BeginUndoStep("Set Selection Mode");
    try
    {
        // Add a ToolWindow where we can put some buttons.
        ToolWindow tw = new ToolWindow();
        tw.Caption = "New ToolWindow";
        // Add it docked to the right of the screen.
        UIEnvironment.Windows.AddDocked(tw, DockStyle.Right);

        // Create the buttons.
        Button btn = new Button();
        // Set the text of the button.
        btn.Text = "Select surface";
        // Set the size of the button.
        btn.Size = new Size(190, 40);
        // Set the location of the button (pixels from top left corner).
        btn.Location = new Point(5, 5);
        // Add an event handler to the button.
        btn.Click += new EventHandler(btn1_clicked);
        // Add the button to the ToolWindow.
        tw.Control.Controls.Add(btn);

        // Create a new button.
        Button btn2 = new Button();
        btn2.Text = "Select part";
        btn2.Size = new Size(190, 40);
        btn2.Location = new Point(5, 50);
        btn2.Click += new EventHandler(btn2_clicked);
        tw.Control.Controls.Add(btn2);

        // And one more button.
        Button btn3 = new Button();
        btn3.Text = "Select mechanism";
        btn3.Size = new Size(190, 40);
        btn3.Location = new Point(5, 95);
        btn3.Click += new EventHandler(btn3_clicked);
        tw.Control.Controls.Add(btn3);

        // And yet another button.
        Button btn4 = new Button();
        btn4.Text = "Select disabled";
        btn4.Size = new Size(190, 40);
        btn4.Location = new Point(5, 140);
        btn4.Click += new EventHandler(btn4_clicked);
        tw.Control.Controls.Add(btn4);
    }
    catch
    {
        Project.UndoContext.CancelUndoStep(CancelUndoStepType.Rollback);
        throw;
    }
    finally
    {
        Project.UndoContext.EndUndoStep();
    }
}

// The event handler for the first button.
static void btn1_clicked(object sender, EventArgs e)
{
    // Call the method that sets the SelectionMode.
    // See further down for this method.
    SetSelectionMode(SelectionModes.Surface);
}

// The event handler for the second button.
static void btn2_clicked(object sender, EventArgs e)
{
    // Call the method that sets the SelectionMode.
    // See further down for this method.
    SetSelectionMode(SelectionModes.Part);
}

// The event handler for the third button.
static void btn3_clicked(object sender, EventArgs e)
{
    // Call the method that sets the SelectionMode.
    // See further down for this method.
    SetSelectionMode(SelectionModes.Mechanism);
}

// The event handler for the fourth button.
static void btn4_clicked(object sender, EventArgs e)
{
    // Call the method that sets the SelectionMode.
    // See further down for this method.
    SetSelectionMode(SelectionModes.Disable);
}

// This method sets the selection level.
static void SetSelectionMode(SelectionModes mode)
{
    // Go through all present windows.
    foreach (Window w in UIEnvironment.Windows)
    {
        // If there is a DocumentWindow that contains a GraphicControl
        if ((w is DocumentWindow) && (w.Control is GraphicControl))
        {
            // Set the SelectionMode.
            GraphicControl gc = w.Control as GraphicControl;
            if (gc != null)
                gc.Picker.SelectionMode = mode;
        }
    }
}