How to nest sub panels and submenus on the TOOLS panel (T)?

Question

Hi, I´m aiming to create panels with menus and submenus in the TOOLS area type just like in the picture to the LEFT. Blender pops up a shortcut menu (with shift+a) and I see it´s got arrows pointing to a submenu populated with options.

I saw the py demos on the text editor, but none of those make a main panel nesting sub panels. I want to be able to contract/expand the panel and thus reveal or hide the subPanels. The 2nd level of menu branching will

Answer 1

Declare as many menus as you like and concatenate them by calling each menu within the previous menu by layout.menu(menu_identifier).

You can even automatically draw a button to call your menu without declaring any extra operator by layout.operator("wm.call_menu").name="menu_identifier".

---

Code ripped from How to create a custom UI? and combined with Templates > Python > Ui Menu.

bl_info = {
    "name": "Add-on Template",
    "description": "",
    "author": "",
    "version": (0, 0, 1),
    "blender": (2, 70, 0),
    "location": "3D View > Tools",
    "warning": "", # used for warning icon and text in addons panel
    "wiki_url": "",
    "tracker_url": "",
    "category": "Development"
}

import bpy

# ------------------------------------------------------------------------
#    custom menus
# ------------------------------------------------------------------------

class MyCustomMenu(bpy.types.Menu):
    bl_label = "First Menu"
    bl_idname = "OBJECT_MT_custom_menu"

    def draw(self, context):
        layout = self.layout
        layout.label(text="Hello First Menu!", icon='WORLD_DATA')

         # call the second custom menu
        layout.menu("OBJECT_MT_sub_menu", icon="COLLAPSEMENU")

        # use an operator enum property to populate a sub-menu
        layout.operator_menu_enum("object.select_by_type",
                                  property="type",
                                  text="Select All Objects by Type...",
                                  )

class MyCustomSubMenu(bpy.types.Menu):
    bl_label = "Sub Menu"
    bl_idname = "OBJECT_MT_sub_menu"

    def draw(self, context):
        layout = self.layout
        layout.label(text="Hello Second Menu!", icon='WORLD_DATA')

        # call another menu
        layout.operator("wm.call_menu", text="Unwrap").name = "VIEW3D_MT_uv_map"

        # just for fun call the first one again
        layout.menu("OBJECT_MT_sub_sub_menu", icon="COLLAPSEMENU")


class MyCustomSubSubMenu(bpy.types.Menu):
    bl_label = "Sub Sub Menu"
    bl_idname = "OBJECT_MT_sub_sub_menu"

    def draw(self, context):
        layout = self.layout
        layout.label(text="Hello Third Menu!", icon='WORLD_DATA')    


# ------------------------------------------------------------------------
#    my tool in objectmode
# ------------------------------------------------------------------------

class OBJECT_PT_my_panel(bpy.types.Panel):
    bl_idname = "OBJECT_PT_my_panel"
    bl_label = "My Panel"
    bl_space_type = "VIEW_3D"   
    bl_region_type = "TOOLS"    
    bl_category = "Tools"
    bl_context = "objectmode"   
    '''
    @classmethod
    def poll(self,context):
        return context.object is not None
    '''
    def draw(self, context):
        layout = self.layout
        scene = context.scene
        mytool = scene.my_tool

        layout.prop(mytool, "my_int")
        layout.prop(mytool, "my_enum", text="")
        layout.operator("wm.call_menu", text="Call My Menu").name = "OBJECT_MT_custom_menu"


# ------------------------------------------------------------------------
#    settings
# ------------------------------------------------------------------------

class MySettings(bpy.types.PropertyGroup):

    my_int = bpy.props.IntProperty(
        name = "Int Value",
        description="A integer property",
        default = 23,
        min = 10,
        max = 100
        )

    my_enum = bpy.props.EnumProperty(
        name="Dropdown:",
        description="Apply Data to attribute.",
        items=[ ('OP1', "Option 1", ""),
                ('OP2', "Option 2", ""),
                ('OP3', "Option 3", ""),
               ]
        )

# ------------------------------------------------------------------------
#    register and unregister the classes
# ------------------------------------------------------------------------

def register():
    bpy.utils.register_module(__name__)
    bpy.types.Scene.my_tool = bpy.props.PointerProperty(type=MySettings)

def unregister():
    bpy.utils.unregister_module(__name__)
    del bpy.types.Scene.my_tool

if __name__ == "__main__":
    register()

    # The menu can also be called from scripts
    # bpy.ops.wm.call_menu(name=CustomMenu.bl_idname)