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CHAPTER 11 CREATING CUSTOM WIDGETS
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Lastly, the MyIPAddress widget is connected to two signals. The key-press-event callback function will filter the keys that the widget will react to. Then, when cursor-position changes, the position will be updated, so we can control where text is entered. Remember that, since MyIPAddress is derived from GtkEntry, it inherits all of its members, properties, signals, functions, and so on. It also inherits everything from GtkWidget, GtkObject, and GObject, since those classes are its ancestors. Next, a few private functions are implemented that will handle how the widget interacts with the user. Listing 11-11 shows a function called my_ip_address_render(). This function builds a string out of the IP address values and adds it to the GtkEntry widget. This is the only function that will write to the GtkEntry widget. Listing 11-11. Rendering the MyIPAddress Widget /* Render the current content of the IP address in the GtkEntry widget. */ static void my_ip_address_render (MyIPAddress *ipaddress) { MyIPAddressPrivate *priv = MY_IP_ADDRESS_GET_PRIVATE (ipaddress); GString *text; guint i; /* Create a string that displays the IP address content, adding spaces if a * number cannot fill three characters. */ text = g_string_new (NULL); for (i = 0; i < 4; i++) { gchar *temp = g_strdup_printf ("%3i.", priv->address[i]); text = g_string_append (text, temp); g_free (temp); } /* Remove the trailing decimal place and add the string to the GtkEntry. */ text = g_string_truncate (text, 15); gtk_entry_set_text (GTK_ENTRY (ipaddress), text->str); g_string_free (text, TRUE); } This function uses GString to build a fifteen-character IP address string out of three periods and the four integers that are currently stored in the instance of MyIPAddressPrivate. This string will be displayed to the user in the GtkEntry widget. If an integer does not fill up three spaces, it is padded with one or two space characters so that the IP address will always have a width of fifteen characters. This allows us to know exactly where the cursor should be placed at all times, since the width is guaranteed.
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CHAPTER 11 CREATING CUSTOM WIDGETS
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The MyIPAddress widget is built so that the cursor is forced to one of four positions. Each number is always aligned to the right and padded with spaces on the left if necessary. Because of this, the cursor is forced into the position on the right of one of the four numbers. This is done in the notify::cursor-position callback function displayed in Listing 11-12. Listing 11-12. Callback Functions for MyIPAddress /* Force the cursor to always be at the end of one of the four numbers. */ static void my_ip_address_move_cursor (GObject *entry, GParamSpec *spec) { gint cursor = gtk_editable_get_position (GTK_EDITABLE (entry)); if (cursor <= 3) gtk_editable_set_position else if (cursor <= 7) gtk_editable_set_position else if (cursor <= 11) gtk_editable_set_position else gtk_editable_set_position } /* Handle key presses of numbers, tabs, backspaces and returns. */ static gboolean my_ip_address_key_pressed (GtkEntry *entry, GdkEventKey *event) { MyIPAddressPrivate *priv = MY_IP_ADDRESS_GET_PRIVATE (entry); guint k = event->keyval; gint cursor, value; /* If the key is an integer, append the new number to the address. This is only * done if the resulting number will be less than 255. */ if ((k >= GDK_0 && k <= GDK_9) || (k >= GDK_KP_0 && k <= GDK_KP_9)) { cursor = floor (gtk_editable_get_position (GTK_EDITABLE (entry)) / 4); value = g_ascii_digit_value (event->string[0]); if ((priv->address[cursor] == 25) && (value > 5)) return TRUE;
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(GTK_EDITABLE (entry), 3); (GTK_EDITABLE (entry), 7); (GTK_EDITABLE (entry), 11); (GTK_EDITABLE (entry), 15);
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CHAPTER 11 CREATING CUSTOM WIDGETS
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if (priv->address[cursor] < 26) { priv->address[cursor] *= 10; priv->address[cursor] += value; my_ip_address_render (MY_IP_ADDRESS (entry)); gtk_editable_set_position (GTK_EDITABLE (entry), (4 * cursor) + 3); g_signal_emit_by_name ((gpointer) entry, "ip-changed"); } } /* Move to the next number or wrap around to the first. */ else if (k == GDK_Tab) { cursor = (floor (gtk_editable_get_position (GTK_EDITABLE (entry)) / 4) + 1); gtk_editable_set_position (GTK_EDITABLE (entry), (4 * (cursor % 4)) + 3); } /* Delete the last digit of the current number. This just divides the number by * 10, relying on the fact that any remainder will be ignored. */ else if (k == GDK_BackSpace) { cursor = floor (gtk_editable_get_position (GTK_EDITABLE (entry)) / 4); priv->address[cursor] /= 10; my_ip_address_render (MY_IP_ADDRESS (entry)); gtk_editable_set_position (GTK_EDITABLE (entry), (4 * cursor) + 3); g_signal_emit_by_name ((gpointer) entry, "ip-changed"); } /* Activate the GtkEntry widget, which corresponds to the activate signal. */ else if ((k == GDK_Return) || (k == GDK_KP_Enter)) gtk_widget_activate (GTK_WIDGET (entry)); return TRUE; } Listing 11-12 also includes a second function, my_ip_address_key_pressed(), which is called when the key-press-event signal is emitted. It handles specific keys, ignoring all of the rest. For example, number keys are handled, but all letters and symbols are ignored. We will walk through each set of keys that is handled one at a time. The first conditional handles numbers pressed on the keyboard, whether along the top or in the keypad, as defined in <gdk/gdkkeysyms.h>. GDK_KP_# corresponds to the digit keys on the number pad, and GDK_# corresponds to the digit keys along the top of the keyboard, both of which must be accounted for in the conditional statement.
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