How can I add elements to a sizer in wx.Python without having to resize the frame?

Question

I'm developing a project for the university but I don't find a way to add elements to a GridSizer and show them in their position without having to resize the frame. I would want to have predefined space for the GridSizer even if it's empty so I can see the change without resizing, but I don't find how to do it. This images show what happens

Before resizing the frame

After resizing the frame

I know that the panel doesn't because at the beggining the GridSizer was empty Here's my code:

class MyFrame(wx.Frame):

def generarListadoNiveles(self):
    cantidad_niveles = int(self.niveles[0])
    
    if (self.modo == 'inicio'):
        fich_niveles = open('niveles.txt','r')
        niveles = fich_niveles.readlines()
        cantidad_niveles = int(niveles[0])

        #Existe un fichero 'records.txt'
        if (os.path.isfile('records.txt') == True):
            fich_records = open('records.txt','r')
            records = fich_records.readlines()

        #No existe un fichero 'records.txt'
        else:
            fich_records = open('records.txt', 'w')
            fich_records.write('1' + '\n')
            for i in range (cantidad_niveles):
                fich_records.write('_' + '\n')
            fich_records.close()
            fich_records = open('records.txt', 'r')
            records = fich_records.readlines()
            
    #Generar listado de niveles a elegir
    niveles_validos = []
    niveles = (open('records.txt','r')).readlines()
    for i in range (1, int(niveles[0])+2):
        nivel = niveles[i]
        nivel = nivel.rstrip('\n')
        if (nivel == '_'):
            nivel = 'Nivel ' + str(i) + ': ' + 'sin record'
        else:
            nivel = 'Nivel ' + str(i) + ': ' + str(nivel) + 'ptos'
    
        niveles_validos.append(nivel)
        
    return niveles_validos

def __init__(self, *args, **kwds):
    # begin wxGlade: MyFrame.__init__
    kwds["style"] = kwds.get("style", 0) | wx.DEFAULT_FRAME_STYLE
    wx.Frame.__init__(self, *args, **kwds)
    self.SetSize((720,480))
    
    self.lista_opciones = wx.ListBox(self, wx.ID_ANY, choices=[])
    self.boton_comenzar = wx.Button(self, wx.ID_ANY, "Comenzar")
    self.boton_deshacer = wx.Button(self, wx.ID_ANY, "Deshacer")

    self.__set_properties()
    self.__do_layout()
    self.inicio()
    # end wxGlade

def inicio(self):
    #Establecer modo inicio
    self.modo = 'inicio'
    
    #Guardar coches de cada nivel
    self.niveles = (open('niveles.txt','r')).readlines()
    self.coches_niveles = []
    for i in range (10):
        self.coches_niveles.append([])
    nivel = -1
    for i in range (1,len(self.niveles)):
        aux = str(self.niveles[i])
        if '0' <= (aux[0]) <= '9':
            nivel += 1
        else:
            self.coches_niveles[nivel].append(aux)
    
    
    #Opciones de lista de niveles
    listado = self.generarListadoNiveles()
    for i in range (len(listado)):
        elemento = listado[i]
        self.lista_opciones.Append(listado[i])
    
    self.lista_opciones.Bind(wx.EVT_LISTBOX, self.manejarNivel)
        
    #Desactivar botón de deshacer
    self.boton_deshacer.Disable()
    
    #Mensaje de seleccionar nivel
    self.texto_mensajes.SetLabel("Elija un nivel y pulse comenzar para empezar a jugar")
    
    #Añadir eventos
    
    
def __set_properties(self):
    # begin wxGlade: MyFrame.__set_properties
    self.SetTitle("frame")
    # end wxGlade


def __do_layout(self):
    # begin wxGlade: MyFrame.__do_layout
    sizer_1 = wx.BoxSizer(wx.HORIZONTAL) 
    sizer_3 = wx.BoxSizer(wx.HORIZONTAL) 
    self.grid_sizer_1 = wx.GridSizer(8, 8, 0, 0 | wx.EXPAND)
    
    #Sizer de parte izquierda
    sizer_2 = wx.BoxSizer(wx.VERTICAL)
    sizer_2.Add(self.lista_opciones, 0, wx.EXPAND, 0)
    sizer_2.Add(self.boton_comenzar, 0, wx.ALIGN_CENTER, 0)
    sizer_2.Add(self.boton_deshacer, 0, wx.ALIGN_CENTER, 0)
    
        
    texto_contador = wx.StaticText(self, wx.ID_ANY, "Tiempo restante (segundos): ")
    self.texto_mensajes = wx.StaticText(self, wx.ID_ANY, "")
    sizer_2.Add(texto_contador, 1, wx.ALIGN_CENTER, 0)
    sizer_2.Add(self.texto_mensajes, 0, 0, 0)
    

    sizer_1.Add(sizer_2, 1, wx.EXPAND, 0)
    sizer_1.Add(sizer_3, 1, wx.EXPAND, 0)
    
    
    sizer_3.Add(self.grid_sizer_1, 1, wx.EXPAND, 0)
    self.SetSizer(sizer_1)
    self.Layout()
        
        
def crearTablero(self, nivel):
    self.tablero = Tablero(self.nivel_actual)
    lista_coches = self.coches_niveles[self.nivel_actual-1]
    #Añadir los coches al tablero
    abc = ord('A')
    for i in range (len(lista_coches)):
        aux = lista_coches[i]
        coche = Coche(chr(abc),aux[0],aux[1],aux[2],aux[3]) #Orientación,columna,fila,longitud
        self.tablero.insertar_coche(coche)
        abc += 1

    self.visualizarTablero()
    
def visualizarTablero(self):
    matriz = self.tablero.get_estado_matriz()
    
    for i in range (8):
        if i == 0: 
            for j in range (8):
                panel = wx.Panel(self, wx.ID_ANY)
                panel.SetBackgroundColour(wx.Colour(155, 64, 64))
                self.grid_sizer_1.Add(panel, 1, wx.EXPAND, 0)
            
#EVENTOS

def manejarNivel(self, event):
    if (self.modo == 'inicio'):
        self.nivel_actual = self.lista_opciones.GetSelection() + 1
        print(self.nivel_actual)
        self.crearTablero(self.nivel_actual)

Answer 1

After you added the panels to your gridsizer, you need to call Layout() on your frame to see your freshly added windows in their proper place.

self.Layout()

If there are too many Layout() calls in any case, you could see the child windows added one by one, you can do the following against it: Freeze your frame, and thaw it after.

self.Freeze()

#self.Layout() calls

self.Thaw()