How display and use operator properties in a Python Blender UI panel?

Question

I have try to make an UI Panel with my operator, but i can not create a panel with the 2 choices (axis and widht).

I can create a button who launch a menu in the tools pannel, and the operator works fine with this :

layout = self.layout
layout.operator(ChooseAxis.bl_idname)

But i want to have exactly this menu in the UI panel, not in tools, so I have try to write this :

layout.prop(obj, "axis")
layout.prop(obj, "newdim")

But that doesn't works, values ​​are modifiable but are ignored and do not modify the object.

How can i have the operator directly on the UI Panel ? (Not a button to launch the operator, but the operator himself with its Properties.)

Moreover, how i can keep the object size value when i launch the operator ? Because when i launch it, it the default value of the newdim property is set to 1 (for example), the object is directly resized. Is it possible to have a default="object actual value" ?

here the entire script with the ui panel created :

from bpy import *
import bpy
from bpy.props import FloatProperty, EnumProperty

class ProportionalDimensions(bpy.types.Panel):
    """Creates a Panel in the Object UI window"""
    bl_label = "Proportional Dimensions"
    bl_idname = "prop_dim"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    #bl_context = "object"
    
    def draw(self, context):
        obj = context.object
    
        #row = layout.row()
        #row.label(text="Active object is: " + obj.name)
  
        layout = self.layout
        layout.operator(ChooseAxis.bl_idname)

        layout.prop(obj, "axis")
        layout.prop(obj, "newdim")


class ChooseAxis(bpy.types.Operator):
    bl_idname = "object.choose_axis"
    bl_label = "Choose_the_Right_Axis"
    bl_description = "This is to choose the axis"
    bl_options = {'REGISTER', 'UNDO'}

    axis: EnumProperty(
        name="Axis",
        description="Axis selection",
        items= [('x', "X", ""),('y', "Y", ""),('z', "Z","")],
        default='x'
        )

    newdim: FloatProperty(
        name="Width",
        description="Scale",
        min=0.01, max=100.0,
        default=1,
        )
    # your code
    def scale(self, axis, new_dim):
        ob = bpy.context.active_object
        d = ob.dimensions

        x = d[0]
        y = d[1]
        z = d[2]

        scale =  axis

        if( scale == "x"):
            indice = 0
        elif( scale == "y"):
            indice = 1
        else:
            indice = 2

        old_dim = d[indice] 
        factor = new_dim / old_dim

        scale_x = ob.scale[0]
        scale_y = ob.scale[1]
        scale_z = ob.scale[2]

        ob.scale[0] = scale_x * factor
        ob.scale[1] = scale_y * factor
        ob.scale[2] = scale_z * factor

def execute(self, context):
    self.scale(self.axis,self.newdim)
    return {'FINISHED'}

def register():
    bpy.utils.register_class(ProportionalDimensions)
    bpy.utils.register_class(ChooseAxis)
   
    
def unregister():
    bpy.utils.unregister_class(ProportionalDimensions)
    bpy.utils.unregister_class(ChooseAxis)
    
if __name__ == "__main__":
    register()

Answer 1

You usually run an operator and adjust the settings afterwards in the Redo panel, or the operator should prompt the user before execution using invoke_props_dialog():

import bpy

class SimpleOperator(bpy.types.Operator):
    bl_label = "Simple Operator"
    bl_idname = "object.simple_operator"
    
    my_enum: bpy.props.EnumProperty(
        items=(
            ('ONE', "One", ""),
            ('TWO', "Two", ""),
            ('THREE', "Three", "")
        ),
        default='ONE'
    )
    
    def invoke(self, context, event):
        wm = context.window_manager
        return wm.invoke_props_dialog(self)
    
    def execute(self, context):
        self.report({'INFO'}, self.my_enum)
        return {'FINISHED'}


def register():
    bpy.utils.register_class(SimpleOperator)

def unregister():
    bpy.utils.unregister_class(SimpleOperator)

if __name__ == "__main__":
    register()

    bpy.ops.object.simple_operator('INVOKE_DEFAULT')

If you really want to display UI elements in a panel to be set before clicking the button, you will have to register global properties and pass them to the according operator properties (you can't add operator properties to a panel).

import bpy

class SimpleOperator(bpy.types.Operator):
    bl_label = "Simple Operator"
    bl_idname = "object.simple_operator"
    
    my_enum: bpy.props.EnumProperty(
        items=(
            ('ONE', "One", ""),
            ('TWO', "Two", ""),
            ('THREE', "Three", "")
        ),
        default='ONE'
    )
    
    def execute(self, context):
        self.report({'INFO'}, self.my_enum)
        return {'FINISHED'}


class HelloWorldPanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Hello World Panel"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "object"
    
    def draw(self, context):
        layout = self.layout

        ob = context.object

        row = layout.row()
        row.prop(ob, "my_global_enum", expand=True)
        
        props = layout.operator(SimpleOperator.bl_idname)
        props.my_enum = ob.my_global_enum


def register():
    bpy.utils.register_class(SimpleOperator)
    bpy.utils.register_class(HelloWorldPanel)
    
    bpy.types.Object.my_global_enum = bpy.props.EnumProperty(
        items=(
            ('ONE', "One", ""),
            ('TWO', "Two", ""),
            ('THREE', "Three", "")
        ),
        default='TWO'
    )


def unregister():
    bpy.utils.unregister_class(HelloWorldPanel)
    bpy.utils.unregister_class(SimpleOperator)
    del bpy.types.Object.my_global_enum


if __name__ == "__main__":
    register()