c - GTK3开罗g_signal_connect:不明白这一点

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我正在尝试解决此问题，当我单击“ button1”时，将调用“ on_draw_event”功能（有效），并且在“ darea” -drawing_area中显示一行（无效）。

这是我的代码：

    #include <gtk/gtk.h>

static gboolean on_draw_event(GtkWidget *button, cairo_t *darea)
{
    printf ("function: on_draw_event\n");
    cairo_set_source_rgb(darea, 0, 255, 0);
    cairo_set_line_width(darea, 0.5);

    cairo_move_to(darea, 0, 100);
    cairo_line_to(darea, 400, 100);
    cairo_stroke(darea);
    return FALSE;
}


int main (int argc, char *argv[])
{
    GtkWidget *window;
    GtkWidget *darea;
    GtkWidget *myGrid;
    GtkWidget *button1;
    GtkWidget *button2;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_POPUP);
    myGrid = gtk_grid_new ();
    darea = gtk_drawing_area_new();

    gtk_widget_set_size_request(darea, 400, 400);
    button1 = gtk_button_new_with_label ("BUTTON 1");
    button2 = gtk_button_new_with_label ("QUIT");

    gtk_grid_attach(GTK_GRID(myGrid), button1, 0, 0, 1, 1);
    gtk_grid_attach(GTK_GRID(myGrid), darea, 0, 1, 1, 1);
    gtk_grid_attach(GTK_GRID(myGrid), button2, 0, 2, 1, 1);
    gtk_container_add(GTK_CONTAINER(window), myGrid);

    g_signal_connect(G_OBJECT(button2), "clicked", G_CALLBACK(gtk_main_quit), NULL);
    g_signal_connect(button1, "clicked", G_CALLBACK(on_draw_event), darea);

    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);

    gtk_widget_show_all(window);

    gtk_main();

    return 0;
}

如果我能
“ g_signal_connect（button1，” clicked“，G_CALLBACK（on_draw_event），darea）;”
至
“ g_signal_connect（G_OBJECT（darea），”绘制“，G_CALLBACK（on_draw_event），NULL）；”
线将被绘制，但我希望它等待我的按钮单击。希望有人可以阻止我，这不是大问题。

谢谢。

最佳答案

如前所述，由于将图形回调连接到clicked信号，因此示例崩溃。调用时，回调将获得荒谬的参数并死亡。

要“等待按钮单击”，请引入一个标志，告诉您按钮是否已单击。在on_draw_event中查询该标志，并在按钮的clicked回调中进行设置。

修改为实现上述示例的示例如下所示：

#include <gtk/gtk.h>

static gboolean on_draw_event(GtkWidget *darea, cairo_t *cr,
                              gboolean *draw_line)
{
    if (!*draw_line)
        return FALSE;
    printf ("function: on_draw_event\n");
    cairo_set_source_rgb(cr, 0, 255, 0);
    cairo_set_line_width(cr, 0.5);

    cairo_move_to(cr, 0, 100);
    cairo_line_to(cr, 400, 100);
    cairo_stroke(cr);
    return FALSE;
}

static void on_button1_clicked(GtkWidget *button, gboolean *draw_line)
{
    *draw_line = TRUE;
    /* Make sure the widget is repainted after the click.
       gtk_widget_queue_draw() should better be invoked with just the
       drawing area, but this code accesses the common parent for
       simplicity. Passing darea in a struct whose address is provided as
       user_data (along with gboolean *draw_line) is left as exercise. */
    gtk_widget_queue_draw(gtk_widget_get_parent(button));
}


int main (int argc, char *argv[])
{
    GtkWidget *window;
    GtkWidget *darea;
    GtkWidget *myGrid;
    GtkWidget *button1;
    GtkWidget *button2;
    gboolean draw_line = FALSE;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_POPUP);
    myGrid = gtk_grid_new ();
    darea = gtk_drawing_area_new();

    gtk_widget_set_size_request(darea, 400, 400);
    button1 = gtk_button_new_with_label ("BUTTON 1");
    button2 = gtk_button_new_with_label ("QUIT");

    gtk_grid_attach(GTK_GRID(myGrid), button1, 0, 0, 1, 1);
    gtk_grid_attach(GTK_GRID(myGrid), darea, 0, 1, 1, 1);
    gtk_grid_attach(GTK_GRID(myGrid), button2, 0, 2, 1, 1);
    gtk_container_add(GTK_CONTAINER(window), myGrid);

    g_signal_connect(G_OBJECT(button2), "clicked", G_CALLBACK(gtk_main_quit), NULL);
    g_signal_connect(button1, "clicked", G_CALLBACK(on_button1_clicked), &draw_line);
    g_signal_connect(G_OBJECT(darea), "draw", G_CALLBACK(on_draw_event), &draw_line);

    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);

    gtk_widget_show_all(window);

    gtk_main();

    return 0;
}

关于c - GTK3开罗g_signal_connect:不明白这一点，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/34656461/