GTK+ 2.0 Tutorial
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# Spin Buttons

The Spin Button widget is generally used to allow the user to select a value from a range of numeric values. It consists of a text entry box with up and down arrow buttons attached to the side. Selecting one of the buttons causes the value to "spin" up and down the range of possible values. The entry box may also be edited directly to enter a specific value.

The Spin Button allows the value to have zero or a number of decimal places and to be incremented/decremented in configurable steps. The action of holding down one of the buttons optionally results in an acceleration of change in the value according to how long it is depressed.

The Spin Button uses an Adjustment object to hold information about the range of values that the spin button can take. This makes for a powerful Spin Button widget.

Recall that an adjustment widget is created with the following function, which illustrates the information that it holds:

    GtkObject *gtk_adjustment_new( gdouble value,
                                   gdouble lower,
                                   gdouble upper,
                                   gdouble step_increment,
                                   gdouble page_increment,
                                   gdouble page_size );

These attributes of an Adjustment are used by the Spin Button in the following way:

- `value`: initial value for the Spin Button

- `lower`: lower range value

- `upper`: upper range value

- `step_increment`: value to increment/decrement when pressing mouse button 1 on a button

- `page_increment`: value to increment/decrement when pressing mouse button 2 on a button

- `page_size`: unused

Additionally, mouse button 3 can be used to jump directly to the `upper` or `lower` values when used to select one of the buttons. Lets look at how to create a Spin Button:

    GtkWidget *gtk_spin_button_new( GtkAdjustment *adjustment,
                                    gdouble        climb_rate,
                                    guint          digits );

The `climb_rate` argument take a value between 0.0 and 1.0 and indicates the amount of acceleration that the Spin Button has. The `digits` argument specifies the number of decimal places to which the value will be displayed.

A Spin Button can be reconfigured after creation using the following function:

    void gtk_spin_button_configure( GtkSpinButton *spin_button,
                                    GtkAdjustment *adjustment,
                                    gdouble        climb_rate,
                                    guint          digits );

The `spin_button` argument specifies the Spin Button widget that is to be reconfigured. The other arguments are as specified above.

The adjustment can be set and retrieved independantly using the following two functions:

    void gtk_spin_button_set_adjustment( GtkSpinButton  *spin_button,
                                         GtkAdjustment  *adjustment );

    GtkAdjustment *gtk_spin_button_get_adjustment( GtkSpinButton *spin_button );

The number of decimal places can also be altered using:

    void gtk_spin_button_set_digits( GtkSpinButton *spin_button,
                                     guint          digits) ;

The value that a Spin Button is currently displaying can be changed using the following function:

    void gtk_spin_button_set_value( GtkSpinButton *spin_button,
                                    gdouble        value );

The current value of a Spin Button can be retrieved as either a floating point or integer value with the following functions:

    gdouble gtk_spin_button_get_value ( GtkSpinButton *spin_button );

    gint gtk_spin_button_get_value_as_int( GtkSpinButton *spin_button );

If you want to alter the value of a Spin Button relative to its current value, then the following function can be used:

    void gtk_spin_button_spin( GtkSpinButton *spin_button,
                               GtkSpinType    direction,
                               gdouble        increment );

The `direction` parameter can take one of the following values:

      GTK_SPIN_STEP_FORWARD
      GTK_SPIN_STEP_BACKWARD
      GTK_SPIN_PAGE_FORWARD
      GTK_SPIN_PAGE_BACKWARD
      GTK_SPIN_HOME
      GTK_SPIN_END
      GTK_SPIN_USER_DEFINED

This function packs in quite a bit of functionality, which I will attempt to clearly explain. Many of these settings use values from the Adjustment object that is associated with a Spin Button.

`GTK_SPIN_STEP_FORWARD` and `GTK_SPIN_STEP_BACKWARD` change the value of the Spin Button by the amount specified by `increment`, unless `increment` is equal to 0, in which case the value is changed by the value of `step_increment` in theAdjustment.

`GTK_SPIN_PAGE_FORWARD` and `GTK_SPIN_PAGE_BACKWARD` simply alter the value of the Spin Button by `increment`.

`GTK_SPIN_HOME` sets the value of the Spin Button to the bottom of the Adjustments range.

`GTK_SPIN_END` sets the value of the Spin Button to the top of the Adjustments range.

`GTK_SPIN_USER_DEFINED` simply alters the value of the Spin Button by the specified amount.

We move away from functions for setting and retreving the range attributes of the Spin Button now, and move onto functions that affect the appearance and behaviour of the Spin Button widget itself.

The first of these functions is used to constrain the text box of the Spin Button such that it may only contain a numeric value. This prevents a user from typing anything other than numeric values into the text box of a Spin Button:

    void gtk_spin_button_set_numeric( GtkSpinButton *spin_button,
                                      gboolean       numeric );

You can set whether a Spin Button will wrap around between the upper and lower range values with the following function:

    void gtk_spin_button_set_wrap( GtkSpinButton *spin_button,
                                   gboolean       wrap );

You can set a Spin Button to round the value to the nearest `step_increment`, which is set within the Adjustment object used with the Spin Button. This is accomplished with the following function:

    void gtk_spin_button_set_snap_to_ticks( GtkSpinButton  *spin_button,
                                            gboolean        snap_to_ticks );

The update policy of a Spin Button can be changed with the following function:

    void gtk_spin_button_set_update_policy( GtkSpinButton  *spin_button,
                                            GtkSpinButtonUpdatePolicy policy );

The possible values of `policy` are either `GTK_UPDATE_ALWAYS` or `GTK_UPDATE_IF_VALID`.

These policies affect the behavior of a Spin Button when parsing inserted text and syncing its value with the values of the Adjustment.

In the case of `GTK_UPDATE_IF_VALID` the Spin Button value only gets changed if the text input is a numeric value that is within the range specified by the Adjustment. Otherwise the text is reset to the current value.

In case of `GTK_UPDATE_ALWAYS` we ignore errors while converting text into a numeric value.

Finally, you can explicitly request that a Spin Button update itself:

    void gtk_spin_button_update( GtkSpinButton  *spin_button );

It's example time again.

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

    static GtkWidget *spinner1;

    static void toggle_snap( GtkWidget     *widget,
                             GtkSpinButton *spin )
    {
      gtk_spin_button_set_snap_to_ticks (spin, GTK_TOGGLE_BUTTON (widget)->active);
    }

    static void toggle_numeric( GtkWidget *widget,
                                GtkSpinButton *spin )
    {
      gtk_spin_button_set_numeric (spin, GTK_TOGGLE_BUTTON (widget)->active);
    }

    static void change_digits( GtkWidget *widget,
                               GtkSpinButton *spin )
    {
      gtk_spin_button_set_digits (GTK_SPIN_BUTTON (spinner1),
                                  gtk_spin_button_get_value_as_int (spin));
    }

    static void get_value( GtkWidget *widget,
                           gpointer data )
    {
      gchar *buf;
      GtkLabel *label;
      GtkSpinButton *spin;

      spin = GTK_SPIN_BUTTON (spinner1);
      label = GTK_LABEL (g_object_get_data (G_OBJECT (widget), "user_data"));
      if (GPOINTER_TO_INT (data) == 1)
        buf = g_strdup_printf ("%d", gtk_spin_button_get_value_as_int (spin));
      else
        buf = g_strdup_printf ("%0.*f", spin->digits,
                               gtk_spin_button_get_value (spin));
      gtk_label_set_text (label, buf);
      g_free (buf);
    }

    int main( int   argc,
              char *argv[] )
    {
      GtkWidget *window;
      GtkWidget *frame;
      GtkWidget *hbox;
      GtkWidget *main_vbox;
      GtkWidget *vbox;
      GtkWidget *vbox2;
      GtkWidget *spinner2;
      GtkWidget *spinner;
      GtkWidget *button;
      GtkWidget *label;
      GtkWidget *val_label;
      GtkAdjustment *adj;

      /* Initialise GTK */
      gtk_init (&argc, &argv);

      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

      g_signal_connect (G_OBJECT (window), "destroy",
    		    G_CALLBACK (gtk_main_quit),
    		    NULL);

      gtk_window_set_title (GTK_WINDOW (window), "Spin Button");

      main_vbox = gtk_vbox_new (FALSE, 5);
      gtk_container_set_border_width (GTK_CONTAINER (main_vbox), 10);
      gtk_container_add (GTK_CONTAINER (window), main_vbox);

      frame = gtk_frame_new ("Not accelerated");
      gtk_box_pack_start (GTK_BOX (main_vbox), frame, TRUE, TRUE, 0);

      vbox = gtk_vbox_new (FALSE, 0);
      gtk_container_set_border_width (GTK_CONTAINER (vbox), 5);
      gtk_container_add (GTK_CONTAINER (frame), vbox);

      /* Day, month, year spinners */

      hbox = gtk_hbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (vbox), hbox, TRUE, TRUE, 5);

      vbox2 = gtk_vbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);

      label = gtk_label_new ("Day :");
      gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
      gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);

      adj = (GtkAdjustment *) gtk_adjustment_new (1.0, 1.0, 31.0, 1.0,
    					      5.0, 0.0);
      spinner = gtk_spin_button_new (adj, 0, 0);
      gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner), TRUE);
      gtk_box_pack_start (GTK_BOX (vbox2), spinner, FALSE, TRUE, 0);

      vbox2 = gtk_vbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);

      label = gtk_label_new ("Month :");
      gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
      gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);

      adj = (GtkAdjustment *) gtk_adjustment_new (1.0, 1.0, 12.0, 1.0,
    					      5.0, 0.0);
      spinner = gtk_spin_button_new (adj, 0, 0);
      gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner), TRUE);
      gtk_box_pack_start (GTK_BOX (vbox2), spinner, FALSE, TRUE, 0);

      vbox2 = gtk_vbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);

      label = gtk_label_new ("Year :");
      gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
      gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);

      adj = (GtkAdjustment *) gtk_adjustment_new (1998.0, 0.0, 2100.0,
    					      1.0, 100.0, 0.0);
      spinner = gtk_spin_button_new (adj, 0, 0);
      gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner), FALSE);
      gtk_widget_set_size_request (spinner, 55, -1);
      gtk_box_pack_start (GTK_BOX (vbox2), spinner, FALSE, TRUE, 0);

      frame = gtk_frame_new ("Accelerated");
      gtk_box_pack_start (GTK_BOX (main_vbox), frame, TRUE, TRUE, 0);

      vbox = gtk_vbox_new (FALSE, 0);
      gtk_container_set_border_width (GTK_CONTAINER (vbox), 5);
      gtk_container_add (GTK_CONTAINER (frame), vbox);

      hbox = gtk_hbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 5);

      vbox2 = gtk_vbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);

      label = gtk_label_new ("Value :");
      gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
      gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);

      adj = (GtkAdjustment *) gtk_adjustment_new (0.0, -10000.0, 10000.0,
    					      0.5, 100.0, 0.0);
      spinner1 = gtk_spin_button_new (adj, 1.0, 2);
      gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner1), TRUE);
      gtk_widget_set_size_request (spinner1, 100, -1);
      gtk_box_pack_start (GTK_BOX (vbox2), spinner1, FALSE, TRUE, 0);

      vbox2 = gtk_vbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (hbox), vbox2, TRUE, TRUE, 5);

      label = gtk_label_new ("Digits :");
      gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
      gtk_box_pack_start (GTK_BOX (vbox2), label, FALSE, TRUE, 0);

      adj = (GtkAdjustment *) gtk_adjustment_new (2, 1, 5, 1, 1, 0);
      spinner2 = gtk_spin_button_new (adj, 0.0, 0);
      gtk_spin_button_set_wrap (GTK_SPIN_BUTTON (spinner2), TRUE);
      g_signal_connect (G_OBJECT (adj), "value_changed",
    		    G_CALLBACK (change_digits),
    		    (gpointer) spinner2);
      gtk_box_pack_start (GTK_BOX (vbox2), spinner2, FALSE, TRUE, 0);

      hbox = gtk_hbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 5);

      button = gtk_check_button_new_with_label ("Snap to 0.5-ticks");
      g_signal_connect (G_OBJECT (button), "clicked",
    		    G_CALLBACK (toggle_snap),
    		    (gpointer) spinner1);
      gtk_box_pack_start (GTK_BOX (vbox), button, TRUE, TRUE, 0);
      gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE);

      button = gtk_check_button_new_with_label ("Numeric only input mode");
      g_signal_connect (G_OBJECT (button), "clicked",
    		    G_CALLBACK (toggle_numeric),
    		    (gpointer) spinner1);
      gtk_box_pack_start (GTK_BOX (vbox), button, TRUE, TRUE, 0);
      gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE);

      val_label = gtk_label_new ("");

      hbox = gtk_hbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 5);
      button = gtk_button_new_with_label ("Value as Int");
      g_object_set_data (G_OBJECT (button), "user_data", val_label);
      g_signal_connect (G_OBJECT (button), "clicked",
    		    G_CALLBACK (get_value),
    		    GINT_TO_POINTER (1));
      gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 5);

      button = gtk_button_new_with_label ("Value as Float");
      g_object_set_data (G_OBJECT (button), "user_data", val_label);
      g_signal_connect (G_OBJECT (button), "clicked",
    		    G_CALLBACK (get_value),
    		    GINT_TO_POINTER (2));
      gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 5);

      gtk_box_pack_start (GTK_BOX (vbox), val_label, TRUE, TRUE, 0);
      gtk_label_set_text (GTK_LABEL (val_label), "0");

      hbox = gtk_hbox_new (FALSE, 0);
      gtk_box_pack_start (GTK_BOX (main_vbox), hbox, FALSE, TRUE, 0);

      button = gtk_button_new_with_label ("Close");
      g_signal_connect_swapped (G_OBJECT (button), "clicked",
                                G_CALLBACK (gtk_widget_destroy),
    			    G_OBJECT (window));
      gtk_box_pack_start (GTK_BOX (hbox), button, TRUE, TRUE, 5);

      gtk_widget_show_all (window);

      /* Enter the event loop */
      gtk_main ();

      return 0;
    }

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