signal_connect 函数中的指针工作不正确

Question

我想使用 g_signal_connect() 函数更改特定 struct/class 中的数据。所以，在我看来，最好的方法是使用指向 struct 的指针。问题是指针的信息好像一直在变

我花了很多时间来弄清楚为什么会这样，但我不知道。我可以毫无错误地编译和运行代码，但输出总是不同的。

以后想用几个event_box连接一个struct数组或者一个class数组（event_box[0]连接data[0],... ).

我希望有人明白我的意思，我很乐意提供任何帮助。

#include<gtk/gtk.h>

struct d
{
bool status;
int ID;
};

void end_program(GtkWidget *wid, gpointer ptr)
{
gtk_main_quit();
}

void box_click(GtkWidget *wid, gpointer user_data)
{
    struct d *data = (struct d*)user_data;
    printf("status  = %i\n", data->status);
    printf("ID      = %i\n", data->ID);
}

int main (int argc, char *argv[])
{
    struct d data;
    data.status = 0;
    data.ID = 1;

    gtk_init(&argc, &argv);

    GtkWidget *win = gtk_window_new (GTK_WINDOW_TOPLEVEL);

    GtkWidget *event_box  = gtk_event_box_new();
    g_signal_connect(G_OBJECT(event_box), "button_press_event", G_CALLBACK(box_click), &data); 

    gtk_container_add(GTK_CONTAINER(win), event_box);
    gtk_widget_show_all(win);
    g_signal_connect(win, "delete_event", G_CALLBACK(end_program),NULL);

    gtk_main();

    return 0;
}

如果我多次单击该框，输出：

status  = 4
ID      = 32193184
status  = 5
ID      = 32193184
status  = 4
ID      = 32193184
status  = 6
ID      = 32193184
status  = 4
ID      = 32193184

Answer 1

I hope someone understands what I mean and I would be happy about any help.

好吧，是的.. 你为 button-press-event 使用了错误的函数原型。 button-press-event 的原型是：

The “button-press-event” signal

gboolean
user_function (GtkWidget *widget,
               GdkEvent  *event,
               gpointer   user_data)

(注意： 信号是正确的 "button-press-event" 而不是 "button_press_event"，尽管有一个 #define 允许第二种形式工作)

参见 GtkWidget (Gtk+3 Manual)。所以你的函数应该是这样的：

gboolean box_click(GtkWidget *wid, GdkEvent *event, gpointer user_data)
{
    struct d *data = user_data;            /* no need for cast, gpointer is void* */
    g_print("status  = %d\n", data->status);
    g_print("ID      = %d\n", data->ID);

    return TRUE;    /* to prevent further handling, FALSE otherwise */

    (void)wid;      /* cast to void to avoid unused var warning */
    (void)event;
}

额外尼特

使用g_print代替printf，使用gboolean代替bool。虽然传递 address of 适用于小型结构，但对于大型结构，您应该使用 g_slice_new.

进行分配

Answer 2

我将在@David C. Rankin 说的这部分稍微扩展一下：

(void)wid;      /* cast to void to avoid unused var warning */
(void)event;

因为有很多人不知道的重要事情。

cast 的需要一直被错误使用，这是因为还有另一个函数被调用：

g_signal_connect_swapped()

通过将第一个参数与最后一个参数交换来避免这么多转换的需要。

举个例子：

#include <gtk/gtk.h>

GtkWidget *createWindow ( const gint width, const gint height );
void user_function      ( GtkWidget *object, gpointer   user_data );

int main ( void )
{
    GtkWidget *window;
    gtk_init ( NULL, NULL );
    /// ***
    window = createWindow( 300, 300 );
    /// ***
    g_signal_connect ( window, "destroy",       G_CALLBACK( user_function ),  NULL );
    /// ***
    gtk_widget_show_all ( window );
    gtk_main();
}

GtkWidget *createWindow ( const gint width, const gint height )
{
    GtkWidget *window = gtk_window_new  ( GTK_WINDOW_TOPLEVEL );
    gtk_widget_set_size_request ( window, width, height );
    gtk_container_set_border_width ( GTK_CONTAINER ( window ), 50 );
    return window;
}

void user_function ( GtkWidget *object, gpointer   user_data )
{
    (void)object;
    (void)user_data;
    g_print( "Goodbye\n" );
    gtk_main_quit();
}

在这里你可以看到回调函数签名如下所示：

void user_function ( GtkWidget *object, gpointer user_data )

现在在这种情况下需要两个转换，但我们可以通过调用 g_signal_connect_swapped 来删除其中一个（例如 gpointer 数据）：

g_signal_connect_swapped ( window, "destroy", G_CALLBACK( user_function ),  NULL

甚至更好：

g_signal_connect_swapped ( window, "destroy", G_CALLBACK( user_function ),  (gpointer)"Goodbye" );

现在我们的程序是这样的：

#include <gtk/gtk.h>

GtkWidget *createWindow ( const gint width, const gint height );
void user_function      ( gpointer data );

int main ( void )
{
    GtkWidget *window;
    gtk_init ( NULL, NULL );
    /// ***
    window = createWindow( 300, 300 );
    /// ***
    g_signal_connect_swapped ( window, "destroy", G_CALLBACK( user_function ),  (gpointer)"Goodbye" );
    /// ***
    gtk_widget_show_all ( window );
    gtk_main();
}

GtkWidget *createWindow ( const gint width, const gint height )
{
    GtkWidget *window = gtk_window_new  ( GTK_WINDOW_TOPLEVEL );
    gtk_widget_set_size_request ( window, width, height );
    gtk_container_set_border_width ( GTK_CONTAINER ( window ), 50 );
    return window;
}

void user_function ( gpointer data )
{
    g_print( "%s\n", (char*)data );
    gtk_main_quit();
}

而且已经没有 CAST 了。

这是一个更好的例子：

#include <gtk/gtk.h>

gboolean scroll_callback    ( GtkWidget *widget, GdkEvent  *event );
gboolean show_mouse_pressed ( GtkWidget *widget, GdkEventButton *event );

int main ( void )
{
    GtkWidget *window;
    GtkWidget *button;
    gtk_init( NULL, NULL );
    /// ***
    window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
    gtk_window_set_default_size( GTK_WINDOW( window ), 300, 250 );
    g_signal_connect( window, "destroy", gtk_main_quit, NULL );
    gtk_container_set_border_width( GTK_CONTAINER( window ), 50 );
    /// ***
    button = gtk_button_new_with_mnemonic( "_Click me" );

    gtk_widget_add_events( button, GDK_BUTTON_PRESS );
    gtk_widget_add_events( button, GDK_SCROLL_MASK );

    ///g_signal_connect( button, "clicked", gtk_main_quit, NULL );
    gtk_container_add( GTK_CONTAINER( window ), button );
    /// ***
    g_signal_connect_swapped( button, "button_press_event", G_CALLBACK( show_mouse_pressed ), window );
    g_signal_connect_swapped( button, "scroll_event", G_CALLBACK( scroll_callback ), window );
    /// ***
    gtk_widget_show_all( window );
    gtk_main();
}

gboolean scroll_callback ( GtkWidget *widget, GdkEvent  *event )
{
    if ( event->type == GDK_SCROLL ) /// Scroll was Catched ?
    {
        if ( event->scroll.direction == GDK_SCROLL_DOWN ) /// It is down?
        {
            g_print( "Scroll-Down Detected\n" );
            gtk_window_set_title( GTK_WINDOW( widget ), "Scroll-Down Detected" );
        }

        if ( event->scroll.direction == GDK_SCROLL_UP ) /// It is up?
        {
            g_print( "Scroll-UP Detected\n" );
            gtk_window_set_title( GTK_WINDOW( widget ), "Scroll-UP Detected" );
        }
        return FALSE;
    }
    return TRUE;
}

gboolean show_mouse_pressed ( GtkWidget *widget, GdkEventButton *event )
{
    assert ( widget != NULL );
    if ( gtk_widget_get_has_window ( widget ) )
    {
        if ( event->type == GDK_BUTTON_PRESS )
        {
            g_print( "The mouse clicked the button\n" );
            gtk_window_set_title( GTK_WINDOW( widget ),  "The mouse was Clicked" );
        }
        return TRUE;
    }
    return FALSE;
}

signal_connect 函数中的指针工作不正确

The pointer in signal_connect function is not working correct

c

pointers

gtkmm

gtk3