gtk - Image not showing when loaded from file - c++

Question

I am a newbie at GTK+. I want to create a GUI with an Image with 2 buttons and a label below it.
The image has to be loaded via a file dialog which is opened when I click a button called "Load", but the image is not being shown on the Window. Below is my code:
#include <gtk/gtk.h>
#include <gtkmm.h>
#include <glib.h>
#include <cstring>
#include <cstdlib>
#include "cv.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
using namespace std;
using namespace cv;
GtkWidget *window, *image;
GtkWidget *vbox, *valign, *hbox, *halign;
GtkWidget *expression_label;
char* get_file()
{
GtkWidget *dialog = gtk_file_chooser_dialog_new("Open File", (GtkWindow *) window, GTK_FILE_CHOOSER_ACTION_OPEN, GTK_STOCK_CANCEL, GTK_RESPONSE_CANCEL, GTK_STOCK_OPEN, GTK_RESPONSE_ACCEPT, NULL);
if(gtk_dialog_run(GTK_DIALOG(dialog)) == GTK_RESPONSE_ACCEPT)
{
char *filename;
filename = gtk_file_chooser_get_filename( GTK_FILE_CHOOSER(dialog) );
gtk_widget_destroy(dialog);
return filename;
}
}
void load_file(GtkWidget *widget, gpointer data)
{
g_print("Loading file\n");
char *file = get_file();
Mat img = imread(file);
//imshow("Opencv image", img);
image = gtk_image_new_from_file(file);
gtk_widget_queue_draw(image);
// gtk_box_pack_start(GTK_BOX(vbox), image, FALSE, FALSE, 0);
gtk_label_set_text(GTK_LABEL(expression_label), "Image Loaded");
g_print("File Loaded\n");
g_print("%s\n", file);
}
void get_expression(GtkWidget *widget, gpointer data)
{
gtk_label_set_text(GTK_LABEL(expression_label), "Expression Detected");
}
int main(int argc, char* argv[])
{
gtk_init(&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_title(GTK_WINDOW(window), "FEAR");
gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
gtk_window_set_default_size(GTK_WINDOW(window), 1100, 1100);
gtk_window_set_resizable(GTK_WINDOW(window), TRUE);
gtk_container_set_border_width(GTK_CONTAINER(window), 10);
vbox = gtk_vbox_new(FALSE, 5);
hbox = gtk_hbox_new(TRUE, 3);
GtkWidget *load_button = gtk_button_new_with_label("Load");
GtkWidget *run_button = gtk_button_new_with_label("Run");
gtk_widget_set_size_request(load_button, 70, 30);
gtk_widget_set_size_request(run_button, 70, 30);
gtk_container_add(GTK_CONTAINER(hbox), load_button);
gtk_container_add(GTK_CONTAINER(hbox), run_button);
expression_label = gtk_label_new("Expression");
//image = gtk_image_new();
//Display placeholder image
image = gtk_image_new_from_file("../sample.jpg");
gtk_box_pack_start(GTK_BOX(vbox), image, FALSE, FALSE, 0);
gtk_box_pack_start(GTK_BOX(vbox), hbox, FALSE, FALSE, 0);
gtk_box_pack_start(GTK_BOX(vbox), expression_label, FALSE, FALSE, 0);
gtk_container_add(GTK_CONTAINER(window), vbox);
int load_handler_id = g_signal_connect(G_OBJECT(load_button), "clicked", G_CALLBACK(load_file), NULL);
g_signal_connect(G_OBJECT(run_button), "clicked", G_CALLBACK(get_expression), NULL);
g_signal_connect_swapped(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
I basically created a main window, then added a vbox to it. In the vbox, I have added the image widget, a hbox box that holds by buttons and a label widget to give me relevant information.
When I run the program, it displays the placeholder image properly, but when I select "Load" and choose the new image to be displayed, the label changes and I get the correct output on the command line, but the image widget does not display the new image that was selected.
Can someone please help me and let me know what am I doing wrong?

Answer 1

You're getting a new GtkImage widget after loading, and that widget is never added to a window so (of course) it's not being displayed.
You're just overwriting a global widget pointer with the new widget, but that doesn't magically make the new widget "replace" the old in the widget hierarchy. That you store the pointer to the new widget in the variable that used to hold the old widget doesn't matter from GTK+'s perspective.
Replace your call to gtk_image_new_from_file() with a call to gtk_image_set_from_file() on your existing widget (in image) to replace the content of the existing widget, which is packed and so on, with the image from the file.
Also, you're leaking the filename, you need to add free() after using it.
UPDATE: You mention in a comment that you've made the filename a global, to make it available in more places. If so, you still need to free() the old filename before getting a new one, else your code will be leaking memory.