gtk+ Creating new screen problem.

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

#define COMPLETED 1
#define NOT_COMPLETED 0

#define WIDTH 240
#define HEIGHT 320

enum{
	BUY_IT = 0,
	QUANTITY,
	PRODUCT,
	COLUMNS
};


typedef struct{

	gboolean buy;
	gint quantity;
	gchar *product;
}GroceryItem;

const GroceryItem list[] =
{
		{TRUE,1,"Card"},
//		{TRUE,2,"Camera"},
//		{FALSE,1,"Validator"},
//		{FALSE,3,"Recharger"},
		{FALSE,0,NULL},
};

unsigned int firstEnter = NOT_COMPLETED;

GtkWindow *window = NULL;
GtkFixed *appbody = NULL;
GtkFixed *appview = NULL;
GtkFixed *cardinfo = NULL;
GtkFixed *camerainfo = NULL;
GtkFixed *validatorinfo = NULL;
GtkFixed *rechargerinfo = NULL;
GtkFixed *errorinfo = NULL;


static void setup_tree_view(GtkWidget*);

void constructCardInfoScreen(void);
//void constructCameraInfoScreen(void);
//void constructValidatorInfoScreen(void);
//void constructRechargerInfoScreen(void);
//void constructErrorInfoScreen(void);
void constructApplicationWindows(void);
void showScreen(GtkFixed*);


void on_changed(GtkWidget *widget , gpointer data){
	unsigned int i = 0;
		GtkTreeIter iter;
		GtkTreeModel *model;
		char *value;
		if(gtk_tree_selection_get_selected(GTK_TREE_SELECTION(widget),&model,&iter) && (firstEnter != 0)){
			gtk_tree_model_get(model,&iter,PRODUCT,&value,-1);
			while(strcmp(value,list[i].product) != 0){
				i++;
			}
			printf("%s is selected and i = %d \n",value,i);
			switch(i){
				case 0 :
					printf("card info screen is selected ! \n");
					showScreen(cardinfo);
					break;
				case 1 :
					printf("%s is selected \n",value);
					break;
				case 2 :
					printf("%s is selected \n",value);
					break;
				case 3 :
					printf("%s is selected \n",value);
					break;
				default :
					printf("ERR \n");
					break;
			}

			g_free(value);
		}

		firstEnter = COMPLETED;
}

void back_to_main_window(GtkWidget *widget , gpointer data){
	showScreen(appview);
}


int main(int argc , char *argv[]){

	gint i = 0;
	GtkWidget *treeview , *scrolled_win;
	GtkListStore *store;
	GtkTreeIter iter;
	GtkTreeSelection *selection;

	gtk_init(&argc,&argv);
	window = GTK_WINDOW(gtk_window_new(GTK_WINDOW_TOPLEVEL));
	gtk_window_set_position(window , GTK_WIN_POS_CENTER);
	gtk_window_set_title(window ,"Window");
	gtk_widget_set_size_request(GTK_WIDGET(window),WIDTH,HEIGHT);

	appview = GTK_FIXED(gtk_fixed_new());
	gtk_widget_set_size_request(GTK_WIDGET(appview),WIDTH,HEIGHT);

treeview = gtk_tree_view_new(); /* creating tree view */
	setup_tree_view(treeview); /* add three columns to the treeview and show columns as text.*/ /* columns and renderer adjustment */
	store = gtk_list_store_new(COLUMNS,G_TYPE_BOOLEAN,G_TYPE_INT,G_TYPE_STRING); /* tree view columns are set up with desired renderers. so its time to create the tree model that will interface between renderers and the tree view. */ /* we create gtk_list_store */


	while(list[i].product != NULL){
		gtk_list_store_append(store,&iter); /* list store 'u olusturduk. simdi row'u olusturmam\u0131z gerekiyor. row olu\u015fturmay\u0131 gtk_list_store_append ile olusturuyoruz. */
		gtk_list_store_set(store,&iter,BUY_IT,list[i].buy,QUANTITY,list[i].quantity,PRODUCT,list[i].product,-1); /* row'lar\u0131 olusturduktan sonra bu rowlara datalar\u0131 eklememiz gerekmektedir. gtk_list_store_set ile birlikte bu olusturdu\u011fumuz rowlara datalar\u0131 ekliyoruz.*/
		i++;
	}

	gtk_tree_view_set_model(GTK_TREE_VIEW(treeview),GTK_TREE_MODEL(store));
	g_object_unref(store);
	scrolled_win = gtk_scrolled_window_new(NULL,NULL);
	gtk_widget_set_size_request(GTK_WIDGET(scrolled_win),WIDTH,HEIGHT);
	gtk_scrolled_window_set_policy(GTK_SCROLLED_WINDOW(scrolled_win),GTK_POLICY_AUTOMATIC,GTK_POLICY_ALWAYS);
	gtk_container_add(GTK_CONTAINER(scrolled_win),GTK_WIDGET(treeview));
	selection = gtk_tree_view_get_selection(GTK_TREE_VIEW(treeview));
	g_signal_connect(selection,"changed",G_CALLBACK(on_changed),NULL);
	gtk_fixed_put(appview,GTK_WIDGET(scrolled_win),0,0);
	constructApplicationWindows();
	gtk_container_add(GTK_CONTAINER(window),GTK_WIDGET(appview));
	gtk_widget_show_all(GTK_WIDGET(window));
	gtk_main();
	return 0;

}

static void setup_tree_view(GtkWidget *treeview){

	GtkCellRenderer *renderer;
	GtkTreeViewColumn *column;

	renderer = gtk_cell_renderer_text_new();
	column = gtk_tree_view_column_new_with_attributes("Buy",renderer,"text",BUY_IT,NULL);
	gtk_tree_view_append_column(GTK_TREE_VIEW(treeview),column);

	renderer = gtk_cell_renderer_text_new();
	column = gtk_tree_view_column_new_with_attributes("Count",renderer,"text",QUANTITY,NULL);
	gtk_tree_view_append_column(GTK_TREE_VIEW(treeview),column);

	renderer = gtk_cell_renderer_text_new();
	column = gtk_tree_view_column_new_with_attributes("Product",renderer,"text",PRODUCT,NULL);
	gtk_tree_view_append_column(GTK_TREE_VIEW(treeview),column);

}

void constructCardInfoScreen(){
	cardinfo = GTK_FIXED(gtk_fixed_new());
	gtk_widget_set_size_request(GTK_WIDGET(cardinfo),WIDTH,HEIGHT);
	GtkButton *button = (GtkButton *)gtk_button_new_with_label("Cancel");
	gtk_widget_set_size_request(GTK_WIDGET(button),60,60);
	gtk_fixed_put(cardinfo , GTK_WIDGET(button),30,40);
	g_signal_connect(button,"clicked",G_CALLBACK(back_to_main_window),NULL);
}


void showScreen(GtkFixed *screen){
	if(appbody != NULL){
		gtk_widget_hide_all(GTK_WIDGET(appbody));
		gtk_widget_set_sensitive(GTK_WIDGET(screen),TRUE);
	}
	printf("show screen event \n");
	appbody  = screen;
	gtk_widget_show_all(GTK_WIDGET(appbody));
}

void constructApplicationWindows(){

	constructCardInfoScreen();
//	constructCameraInfoScreen();
//	constructValidatorInfoScreen();
//	constructRechargerInfoScreen();
//	constructErrorInfoScreen();
}