import bpy

class MainPanelv2(bpy.types.Panel):
    bl_label = "Object Adder"
    bl_idname = "PT_MainPanel"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = 'Object Adder'

    def draw(self, context):
        layout = self.layout

        row = layout.row()
        row = layout.row()
        row.operator("mesh.primitive_cube_add")
        row = layout.row()
        row = layout.row()
        row.operator("mesh.primitive_cylinder_add")
        row = layout.row()
        row = layout.row()
        row.operator("mesh.primitive_uv_sphere_add")
        row = layout.row()
        row = layout.row()
        #This Operation will add the Selections to your Panel
        row.operator_enum("mesh.select_mode", "type")


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


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


if __name__ == "__main__":
    register()