## class fltk::Button

### Class Hierarchy

    fltk::Widget
       |
       +----fltk::Button
               |
               +----fltk::CheckButton, fltk::LightButton, fltk::RepeatButton,
                    fltk::ReturnButton, fltk::RoundButton

### Include Files

    #include <fltk/Button.h>

### Description

Buttons generate callbacks when they are clicked by the user. You control exactly when and how by changing the values for `type()` and `when()`.

Buttons can also generate callbacks in response to `fltk::SHORTCUT` events. The button can either have an explicit `shortcut()` value or a letter shortcut can be indicated in the `label()` with an '&' character before it. For the label shortcut it does not matter if Alt is held down, but if you have an input field in the same window, the user will have to hold down the Alt key so that the input field does not eat the event first as an `fltk::KEY` event.

### Methods

fltk::Button ~Button | clear down_box | set setonly | type | value when

#### fltk::Button::Button(int x, int y, int w, int h, const char *label = 0)

The constructor creates the button using the position, size, and label.

#### fltk::Button::~Button(void)

The destructor removed the button.

#### int fltk::Button::clear()

Same as `value(0)`.

#### fltk::Box fltk::Button::down_box() const
void fltk::Button::down_box(fltk::Box bt)

The first form returns the current down box type, which is drawn when `value()` is non-zero.

The second form sets the down box type. The default value of 0 causes FLTK to figure out the correct matching down version of `box()`.

#### int fltk::Button::set()

Same as `value(1)`.

#### void fltk::Button::setonly()

Turns on this button and turns off all other radio buttons in the group (calling `value(1)` or `set()` does not do this).

#### uchar fltk::Button::type() const
void fltk::Button::type(uchar t)

The first form of `type()` returns the current button type, which can be one of:

- `0`: The value is unchanged.
- `fltk::TOGGLE`: The value is inverted.
- `fltk::RADIO`: The value is set to 1, and all other buttons in the current group with `type() == fltk::RADIO` are set to zero.

The second form sets the button type to `t`.

#### char fltk::Button::value() const
int fltk::Button::value(int)

The first form returns the current value (0 or 1). The second form sets the current value.

#### fltk::When fltk::Widget::when() const
void fltk::Widget::when(fltk::When w)

Controls when callbacks are done. The following values are useful, the default value is `fltk::WHEN_RELEASE`:

- `0`: The callback is not done, instead changed() is turned on.
- `fltk::WHEN_RELEASE`: The callback is done after the user successfully clicks the button, or when a shortcut is typed.
- `fltk::WHEN_CHANGED` : The callback is done each time the value() changes (when the user pushes and releases the button, and as the mouse is dragged around in and out of the button).