bl_info = {
    "name": "Add-on Template",
    "description": "",
    "author": "p2or",
    "version": (0, 0, 3),
    "blender": (2, 80, 0),
    "location": "3D View > Tools",
    "warning": "", # used for warning icon and text in addons panel
    "wiki_url": "",
    "tracker_url": "",
    "category": "Development"
}


import bpy

from bpy.props import (StringProperty,
                       BoolProperty,
                       IntProperty,
                       FloatProperty,
                       FloatVectorProperty,
                       EnumProperty,
                       PointerProperty,
                       )
from bpy.types import (Panel,
                       Menu,
                       Operator,
                       PropertyGroup,
                       )


# ------------------------------------------------------------------------
#    Scene Properties
# ------------------------------------------------------------------------

def my_callback(scene, context):

    items = [
        ('GA', "Asset", "tooltip"),
        ('LP', "Low", "tooltip"),
        ('HP', "High", "High Poly"),
    ]

    return items


class MyProperties(PropertyGroup):

    my_bool: BoolProperty(
        name="Enable or Disable",
        description="A bool property",
        default = False
        )

    # define asset mode types
    fbx_mode: EnumProperty(
        name="Dropdown:",
        description="Apply Data to attribute.",
        items=my_callback
        )

    # collection spawner
    fbx_spawner: EnumProperty(
        name="File Spawners",
        options={'ENUM_FLAG'},
        items=my_callback,
        description="tooltip",
        )

# ------------------------------------------------------------------------
#    Panel in Object Mode
# ------------------------------------------------------------------------

class OBJECT_PT_CustomPanel(Panel):
    bl_label = "My Panel"
    bl_idname = "OBJECT_PT_custom_panel"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    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_bool")
        layout.prop(mytool, "fbx_mode", text="")

        layout.label(text="Spawner:")

        layout.prop(mytool, "fbx_spawner") #?
        # Alternatively expand the property:
        layout.prop(mytool, "fbx_mode", expand=True)

        layout.separator()

# ------------------------------------------------------------------------
#    Registration
# ------------------------------------------------------------------------

classes = (
    MyProperties,
    OBJECT_PT_CustomPanel
)

def register():
    from bpy.utils import register_class
    for cls in classes:
        register_class(cls)

    bpy.types.Scene.my_tool = PointerProperty(type=MyProperties)

def unregister():
    from bpy.utils import unregister_class
    for cls in reversed(classes):
        unregister_class(cls)
    del bpy.types.Scene.my_tool


if __name__ == "__main__":
    register()