Question

我正在研究一个项目，我试图通过向它们传递相同的变量（回调共享相同的变量）使2个回调相互通信。由于回调函数不能返回值，因此我传递了一个指向主循环（main函数）中赋值的指针。但是，它根本不起作用！

这是我的代码：

#include <gtk/gtk.h>

static void inc_val (GtkWidget *widget, gpointer data)
{
    int* value =  data;
    *value++;
    printf("value is: %d\n", *value);
}

static void inc_val_ten (GtkWidget *widget, gpointer data)
{
    int* value =  data;
    *value+=10;
    printf("value is: %d\n", *value);
}

static void activate (GtkApplication *app, gpointer user_data)
{
    GtkWidget *window;
    GtkWidget *grid;
    GtkWidget *button;
    int value = 0;

    window = gtk_application_window_new (app);
    gtk_window_set_title (GTK_WINDOW (window), "Window");
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);

    grid = gtk_grid_new ();
    gtk_container_add (GTK_CONTAINER (window), grid);

    button = gtk_button_new_with_label ("Add 1 to value");
    g_signal_connect (button, "clicked", G_CALLBACK (inc_val), &value);
    gtk_grid_attach (GTK_GRID (grid), button, 0, 0, 1, 1);

    button = gtk_button_new_with_label ("Add 10 to value");
    g_signal_connect (button, "clicked", G_CALLBACK (inc_val_ten), &value);
    gtk_grid_attach (GTK_GRID (grid), button, 1, 0, 1, 1);

    button = gtk_button_new_with_label ("Quit");
    g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_widget_destroy), window);
    gtk_grid_attach (GTK_GRID (grid), button, 0, 1, 2, 1);

    gtk_widget_show_all (window);
}

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

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

    return status;
}

该程序在窗口中有3个按钮：

将值1添加到
将值10添加到
退出程序

value是主循环上的整数。当按下其中一个按钮（第一个或第二个）时，值变大（按1或10），程序将打印新值。

我已经运行程序并单击按钮，这就是我所拥有的：

value is: 46525384
value is: 46525384
value is: 46157330
value is: -830528646
value is: 56
value is: 10

而不是：

value is: 1
value is: 2
value is: 12
value is: 22
value is: 23
value is: 33

任何人都知道为什么会这样？

感谢您的帮助！

编辑：我尝试了同样的事情，而不是在数字中添加数字，我尝试将按钮添加到网格中。由于答案（在问题下）的解决方案适用于前面的代码，因此我将网格设为全局。

所以这是新代码：

#include <gtk/gtk.h>
#include <stdlib.h>
#include <stdio.h>

GtkWidget *grid;

static void add_button (GtkWidget *widget, gpointer data)
{
    static int value = 0;
    GtkWidget* grid = data;
    value++;
    printf("attach to line %d\n", value);
    gtk_grid_attach(GTK_GRID(grid), gtk_button_new_from_stock(GTK_STOCK_NEW), 0, value, 1, 1);
}

static void activate (GtkApplication *app, gpointer user_data)
{
    GtkWidget *window;
    GtkWidget *button;

    window = gtk_application_window_new (app);
    gtk_window_set_title (GTK_WINDOW (window), "Window");
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);

    grid = gtk_grid_new ();
    gtk_container_add (GTK_CONTAINER (window), grid);

    button = gtk_button_new_with_label ("Add Button");
    g_signal_connect (button, "clicked", G_CALLBACK (add_button), grid);
    gtk_grid_attach (GTK_GRID (grid), button, 0, 0, 1, 1);

    gtk_widget_show_all (window);
}

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

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

    return status;
}

然而，由于某种原因，它无法正常工作。帮助将不胜感激！

Answer 1

value位于activate的本地。当activate完成时，其局部变量消失了;传递给处理程序的指针现在毫无意义。

解决方案是让value在应用程序的整个生命周期中幸存。最简单（但可能不是最干净）的方法是使其全球化。

Answer 2

回答编辑：

您必须显示小部件才能实现它们。最简单的方法是在父容器上调用gtk_widget_show_all：

static void add_button (GtkWidget *widget, gpointer data)
{
    static int value = 0;
    GtkWidget* grid = data;
    value++;
    printf("attach to line %d\n", value);
    gtk_grid_attach(GTK_GRID(grid), 
    gtk_button_new_from_stock(GTK_STOCK_NEW), 0, value, 1, 1);
    gtk_widget_show_all(grid);
}

另一种选择是保持对按钮的引用并在该实例上调用gtk_widget_show。 e.g：

static void add_button (GtkWidget *widget, gpointer data)
{
    static int value = 0;
    GtkWidget* grid = data;
    GtkWidget* button = gtk_button_new_from_stock(GTK_STOCK_NEW);

    value++;
    printf("attach to line %d\n", value);

    gtk_grid_attach(GTK_GRID(grid), button, 0, value, 1, 1);
    gtk_widget_show (button);
}

如何在gtk + c中回调之间进行通信

2 个答案: