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9.10 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( gfloat value,gfloat lower,gfloat upper,
gfloat step_increment,gfloat page_increment,gfloat 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,
gfloat climb_rate,guintdigits );

　　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,gfloat climb_rate,guintdigits );

　　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,guintdigits);

　　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,gfloat value );

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

gfloat gtk_spin_button_get_value_as_float( GtkSpinButton *spin_button );
gint gtk_spin_button_get_value_as_int( GtkSpinButton *spin_button );

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

void gtk_spin_button_spin( GtkSpinButton *spin_button,
GtkSpinTypedirection,gfloat 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.