How can I configure a GtkWidget signal that runs every time a widget is shown?-CodePudding

The show signal seems to only be called the first time a widget is shown. If I call gtk_widget_show on the widget in question, if it has already been shown, any functions passed to g_signal_connect to the widget in question with the show signal will not be called. I attempted to use the show signal for a button whose text is determined by an external state that the button changes, so when the button first becomes visible it successfully shows the initial state, but even though I change the state in the button handler then call gtk_widget_show, the text is not updated when the button is clicked. How can I configure a widget to run on EVERY show event, not just the first.

CodePudding user response：

Requirement:

update button label based on state
state change happen on button click

One solution could be to update the status when the button is clicked, and then set the button's label, e.g. like this:

update_state();
gtk_button_set_label(button, state);

If more parts of the user interface than just the button should be updated, one could think about introducing a separate function updateUI.

A small demo could look like this:

#include <gtk/gtk.h>

static int cnt;
static char state[16];

static void update_state() {
    snprintf(state, sizeof(state), "clicked %d", cnt  );
}

static void button_show(__unused GtkWidget *widget, __unused gpointer data) {
    g_print("show\n");
}

static void button_clicked(GtkButton *button, __unused gpointer data) {
    g_print("clicked\n");
    update_state();
    gtk_button_set_label(button, state);
}

static void buildUI(GApplication *app, __unused gpointer data) {
    GtkWidget *window = gtk_application_window_new(GTK_APPLICATION(app));
    gtk_window_set_title(GTK_WINDOW(window), "GtkButton");
    gtk_window_set_default_size(GTK_WINDOW(window), 300, 200);
    gtk_container_set_border_width(GTK_CONTAINER(window), 15);
    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);

    GtkWidget *button = gtk_button_new();
    gtk_button_set_label(GTK_BUTTON(button), state);

    gtk_widget_set_size_request(button, 80, 32);

    gtk_widget_set_halign(button, GTK_ALIGN_START);
    gtk_widget_set_valign(button, GTK_ALIGN_START);
    gtk_container_add(GTK_CONTAINER(window), button);

    g_signal_connect(G_OBJECT(button), "clicked",
                     G_CALLBACK(button_clicked), NULL);

    g_signal_connect(G_OBJECT(button), "show",
                     G_CALLBACK(button_show), NULL);

    g_signal_connect(G_OBJECT(window), "destroy",
                     G_CALLBACK(gtk_main_quit), NULL);

    gtk_widget_show_all(GTK_WIDGET(window));
}

int main(int argc, char *argv[]) {
    GtkApplication *app = gtk_application_new("com.example.MyApp", G_APPLICATION_FLAGS_NONE);
    update_state();
    g_signal_connect(app, "activate", G_CALLBACK(buildUI), NULL);
    g_application_run(G_APPLICATION(app), argc, argv);
    g_object_unref(app);
    return 0;
}

It updates the label whenever the button is clicked.