Gtk.Widget.get_allocated_size()窗口显示后创建控件返回零尺寸问题

当调用Gtk.Window.show_all()之后创建GTK控件时，调用Gtk.Widget.get_allocated_size()会返回零尺寸的Gdk.Rectangle。

以下是一个简单示例：窗口内先创建一个按钮，2秒后通过定时器将其替换为更大的按钮：

import gi

gi.require_version("Gtk", "3.0")
from gi.repository import Gtk, GLib


class ButtonWindow(Gtk.Window):
    def __init__(self):
        super().__init__()
        self.set_default_size(500, 200)
        
        button = Gtk.Button.new_with_label("one")
        button.set_size_request(100, 50)
        button.set_halign(Gtk.Align.CENTER)
        button.set_valign(Gtk.Align.CENTER)
        self.add(button)
        
        self.timeout_id = GLib.timeout_add(2000, self.on_timeout, button)

    def on_timeout(self, button):
        rect, _ = button.get_allocated_size()
        print(rect.x, rect.y, rect.width, rect.height)
        
        self.remove(button)
        button = Gtk.Button.new_with_label("two")
        button.set_size_request(200, 100)
        button.set_halign(Gtk.Align.CENTER)
        button.set_valign(Gtk.Align.CENTER)
        self.add(button)
        self.show_all()
        
        rect, _ = button.get_allocated_size()
        print(rect.x, rect.y, rect.width, rect.height)
    
win = ButtonWindow()
win.connect("destroy", Gtk.main_quit)
win.show_all()
Gtk.main()

遗憾的是，即使调用了show_all()且新按钮已可见，get_allocated_size()仍返回新按钮的零尺寸矩形。此外，原按钮返回的分配尺寸实际是窗口的尺寸，控制台输出如下：

0 0 500 200
0 0 0 0

更新 #

该行为在原生GTK3 API中完全一致：

#include <gtk/gtk.h>

guint timeout_id;
GtkWidget *window;
GtkWidget *button;

static gboolean on_timeout(gpointer user_data)
{
    int baseline;
    GtkAllocation rect;
    GtkWidget *button2;
    
    gtk_widget_get_allocated_size(button, &rect, &baseline);
    printf("x: %i y: %i width: %i height: %i\n", rect.x, rect.y, rect.width, rect.height);
    
    gtk_container_remove(GTK_CONTAINER(window), button);
    //g_object_unref (button);  // segfault???
    
    button2 = gtk_button_new_with_label ("two");
    gtk_widget_set_size_request (button2, 200, 100);
    gtk_widget_set_halign (button2, GTK_ALIGN_CENTER);
    gtk_widget_set_valign (button2, GTK_ALIGN_CENTER);
    gtk_container_add (GTK_CONTAINER(window), button2);
    gtk_widget_show_all (window);
    
    gtk_widget_get_allocated_size(button2, &rect, &baseline);
    printf("x: %i y: %i width: %i height: %i\n", rect.x, rect.y, rect.width, rect.height);
    
    g_source_remove(timeout_id);
    return 0;
}

static void activate(GtkApplication* app, gpointer user_data)
{
  window = gtk_application_window_new (app);
  gtk_window_set_default_size (GTK_WINDOW (window), 500, 200);
  
  button = gtk_button_new_with_label ("one");
  gtk_widget_set_size_request (button, 100, 50);
  gtk_widget_set_halign (button, GTK_ALIGN_CENTER);
  gtk_widget_set_valign (button, GTK_ALIGN_CENTER);
  gtk_container_add (GTK_CONTAINER(window), button);
  gtk_widget_show_all (window);
  
  timeout_id = g_timeout_add(2000, on_timeout, NULL);
}

int main(int argc, char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_DEFAULT_FLAGS);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}

输出：

x: 0 y: 0 width: 500 height: 200
x: 0 y: 0 width: 0 height: 0

更新2 #

以下是正确实现的Python版本：

import gi
import time

gi.require_version("Gtk", "3.0")
from gi.repository import Gtk, GLib

class MyButton(Gtk.Button):
    def __init__(self, label, width, height):
        Gtk.Button.__init__(self)
        self.set_label(label)
        self.connect("size-allocate", self.my_size)
        self.set_size_request(width, height)
        self.set_halign(Gtk.Align.CENTER)
        self.set_valign(Gtk.Align.CENTER)
        
    def my_size(self, obj, rect):
        print("Button dimensions", rect.x, rect.y, rect.width, rect.height)
        
class ButtonWindow(Gtk.Window):
    def __init__(self):
        Gtk.Window.__init__(self)
        self.set_default_size(500, 200)
        
        button = MyButton("one", 100, 50)
        self.add(button)
        self.timeout_id = GLib.timeout_add(2000, self.on_timeout, button)

    def on_timeout(self, button):
        self.remove(button)
        button = MyButton("two", 200, 100)
        self.add(button)
        self.show_all()
    
win = ButtonWindow()
win.connect("destroy", Gtk.main_quit)
win.show_all()
Gtk.main()

内容的提问来源于stack exchange，提问作者Olumide