Fl_Choice

The Fl_Choice widget is a button that pops up a menu when clicked, displaying the currently selected value inside the button. It’s commonly used for dropdown selection widgets.

#include <FL/Fl_Choice.H>

Inheritance

Fl_Widget → Fl_Menu_ → Fl_Choice

Constructor

Fl_Choice()

Creates a new choice widget.

Fl_Choice(int X, int Y, int W, int H, const char *label = 0);

int

X coordinate of the widget

int

Y coordinate of the widget

int

Width of the widget

int

Height of the widget

label

const char*

Optional label displayed to the left of the widget

Example:

Fl_Choice *choice = new Fl_Choice(100, 50, 150, 25, "Select:");

Overview

The Fl_Choice widget is similar to Fl_Menu_Button, but with a key difference: the label of the most recently chosen menu item is displayed inside the box, while the widget’s label is displayed outside the box. This makes it ideal for controlling a single variable where you want the user to see the current selection at all glance.

In Motif, this widget is called an OptionButton.

Adding Choices

Using add()

Dynamically add choices:

Fl_Choice *choice = new Fl_Choice(100, 50, 150, 25, "Font:");
choice->add("Helvetica");
choice->add("Times");
choice->add("Courier");
choice->add("Symbol");
choice->value(0);  // Select first item

Simple Example

From the FLTK documentation:

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Choice.H>

int main() {
  Fl_Window *win = new Fl_Window(300, 200);
  Fl_Choice *choice = new Fl_Choice(100, 10, 100, 25, "Choice:");
  choice->add("Zero");
  choice->add("One");
  choice->add("Two");
  choice->add("Three");
  choice->value(2);  // Select "Two" by default (zero-based index)
  win->end();
  win->show();
  return Fl::run();
}

Using Static Array

static Fl_Menu_Item items[] = {
  {"Small"},
  {"Medium"},
  {"Large"},
  {"Extra Large"},
  {0}
};

Fl_Choice *choice = new Fl_Choice(100, 50, 150, 25, "Size:");
choice->copy(items);
choice->value(1);  // Select "Medium"

With User Data

From examples/chart-simple.cxx:

void chart_type_cb(Fl_Widget *w, void*) {
  const Fl_Menu_Item *item = G_choice->mvalue();
  G_chart->type((uchar)item->argument());
  G_chart->redraw();
}

Fl_Choice *choice = new Fl_Choice(140, 470, 200, 25, "Chart Type: ");
choice->add("FL_BAR_CHART",        0, chart_type_cb, (void*)FL_BAR_CHART);
choice->add("FL_HORBAR_CHART",     0, chart_type_cb, (void*)FL_HORBAR_CHART);
choice->add("FL_LINE_CHART",       0, chart_type_cb, (void*)FL_LINE_CHART);
choice->add("FL_FILL_CHART",       0, chart_type_cb, (void*)FL_FILL_CHART);
choice->add("FL_SPIKE_CHART",      0, chart_type_cb, (void*)FL_SPIKE_CHART);
choice->add("FL_PIE_CHART",        0, chart_type_cb, (void*)FL_PIE_CHART);
choice->add("FL_SPECIALPIE_CHART", 0, chart_type_cb, (void*)FL_SPECIALPIE_CHART);
choice->value(0);

Value Methods

value()

Gets or sets the selected item by index.

int value() const;
int value(int index);
int value(const Fl_Menu_Item *item);

index

int

Zero-based index of the item to select. Returns -1 initially if no item selected.

item

const Fl_Menu_Item*

Pointer to the menu item to select

Returns (setter): Non-zero if the value changed, 0 otherwise. Example:

Fl_Choice *choice = new Fl_Choice(100, 50, 150, 25);
choice->add("Red");
choice->add("Green");
choice->add("Blue");

choice->value(1);              // Select "Green"
int selected = choice->value(); // Returns 1

text()

Returns the label of the currently selected item.

const char* text() const;

Returns: Label of the selected item, or NULL if none selected. Example:

const char *selected = choice->text();
if (selected) {
  printf("Selected: %s\n", selected);
}

mvalue()

Returns a pointer to the currently selected menu item.

const Fl_Menu_Item* mvalue() const;

Returns: Pointer to the selected Fl_Menu_Item, or NULL. Example:

const Fl_Menu_Item *item = choice->mvalue();
if (item) {
  printf("Selected: %s\n", item->label());
  long data = item->argument();
}

prev_mvalue()

Returns the previously selected menu item.

const Fl_Menu_Item* prev_mvalue() const;

Returns: Pointer to the previously selected item.

This method is particularly useful for detecting changes in Fl_Choice selections.

Example:

void choice_cb(Fl_Widget *w, void*) {
  Fl_Choice *choice = (Fl_Choice*)w;
  const Fl_Menu_Item *current = choice->mvalue();
  const Fl_Menu_Item *previous = choice->prev_mvalue();
  
  if (previous) {
    printf("Changed from '%s' to '%s'\n", 
           previous->label(), current->label());
  }
}

Callbacks

When a user selects a menu item:

value() is set to that item
If the item has a callback, it’s invoked with:
- The Fl_Choice as the first argument
- The item’s user_data() as the second argument
If the item doesn’t have a callback, the Fl_Choice’s callback is invoked instead

void choice_cb(Fl_Widget *w, void*) {
  Fl_Choice *choice = (Fl_Choice*)w;
  printf("Selected: %s (index %d)\n", choice->text(), choice->value());
}

Fl_Choice *choice = new Fl_Choice(100, 50, 150, 25, "Color:");
choice->callback(choice_cb);
choice->add("Red");
choice->add("Green");
choice->add("Blue");

Item Callbacks

void red_cb(Fl_Widget*, void*)   { printf("Red selected\n"); }
void green_cb(Fl_Widget*, void*) { printf("Green selected\n"); }
void blue_cb(Fl_Widget*, void*)  { printf("Blue selected\n"); }

choice->add("Red",   0, red_cb);
choice->add("Green", 0, green_cb);
choice->add("Blue",  0, blue_cb);

Change Detection

changed()

The inherited changed() flag indicates when the user picks a different value:

int changed() const;        // True when user picks different value
void set_changed();         // Set the changed flag
void clear_changed();       // Clear the changed flag

The changed() flag is automatically cleared just before a callback is invoked and when value() is called.

Example:

void choice_cb(Fl_Widget *w, void*) {
  Fl_Choice *choice = (Fl_Choice*)w;
  // changed() is automatically true when callback is called
  printf("Selection changed to: %s\n", choice->text());
}

Mouse Button Behavior

All three mouse buttons pop up the menu. Unlike some toolkits (Forms), the first two buttons do NOT increment/decrement the choice automatically.

If you need increment/decrement behavior, you can implement it in a subclass.

Events

FL_BEFORE_MENU Event

FLTK triggers an FL_BEFORE_MENU event right before displaying the menu. This provides an opportunity to update menu item states. From test/menubar.cxx:

class Dynamic_Choice : public Fl_Choice {
public:
  Dynamic_Choice(int X, int Y, int W, int H, const char *L = 0)
    : Fl_Choice(X, Y, W, H, L) {}
  
  int handle(int event) override {
    if (event == FL_BEFORE_MENU) {
      // Update menu items before showing
      Fl_Menu_Item *flip = (Fl_Menu_Item*)find_item("Flip");
      Fl_Menu_Item *flop = (Fl_Menu_Item*)find_item("Flop");
      
      if (some_condition()) {
        flip->activate();
        flop->deactivate();
      } else {
        flip->deactivate();
        flop->activate();
      }
    }
    return Fl_Choice::handle(event);
  }
};

Appearance

down_box()

Controls the box type used when the menu is popped up.

Fl_Boxtype down_box() const;
void down_box(Fl_Boxtype boxtype);

Default: FL_DOWN_BOX Example:

choice->down_box(FL_BORDER_BOX);

Text Appearance

// Menu text appearance
choice->textfont(FL_HELVETICA);
choice->textsize(12);
choice->textcolor(FL_BLACK);

// Widget label appearance
choice->labelfont(FL_HELVETICA_BOLD);
choice->labelsize(14);
choice->labelcolor(FL_BLACK);

Box and Color

choice->box(FL_THIN_DOWN_BOX);
choice->color(FL_WHITE);
choice->selection_color(FL_BLUE);

Managing Items

Finding Items

// By label
const Fl_Menu_Item *item = choice->find_item("Medium");

// By index
int index = choice->find_index("Medium");

// By callback
const Fl_Menu_Item *item = choice->find_item(medium_cb);

Modifying Items

// Get item by index
Fl_Menu_Item *item = (Fl_Menu_Item*)&choice->menu()[2];

// Modify item
item->label("Extra Large");
item->activate();
item->deactivate();

// Replace label by index
int index = choice->find_index("Medium");
choice->replace(index, "Medium (Default)");

Removing Items

// Remove by index
int index = choice->find_index("Large");
if (index >= 0) {
  choice->remove(index);
}

// Clear all items
choice->clear();

Item Count

int count = choice->size();
printf("Choice has %d items\n", count);

Complete Example

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Choice.H>
#include <FL/Fl_Box.H>
#include <stdio.h>

Fl_Box *output;

void choice_cb(Fl_Widget *w, void*) {
  Fl_Choice *choice = (Fl_Choice*)w;
  const Fl_Menu_Item *item = choice->mvalue();
  
  if (item) {
    char msg[256];
    sprintf(msg, "Selected: %s (index: %d)", 
            item->label(), choice->value());
    output->copy_label(msg);
  }
}

int main() {
  Fl_Window *win = new Fl_Window(400, 300, "Choice Demo");
  
  // Font choice
  Fl_Choice *font = new Fl_Choice(100, 30, 200, 25, "Font:");
  font->callback(choice_cb);
  font->add("Helvetica");
  font->add("Times");
  font->add("Courier");
  font->add("Symbol");
  font->value(0);
  
  // Size choice
  Fl_Choice *size = new Fl_Choice(100, 70, 200, 25, "Size:");
  size->callback(choice_cb);
  size->add("Small");
  size->add("Medium");
  size->add("Large");
  size->add("Extra Large");
  size->value(1);
  
  // Color choice with user data
  Fl_Choice *color = new Fl_Choice(100, 110, 200, 25, "Color:");
  color->callback(choice_cb);
  color->add("Red",   0, 0, (void*)FL_RED);
  color->add("Green", 0, 0, (void*)FL_GREEN);
  color->add("Blue",  0, 0, (void*)FL_BLUE);
  color->add("Yellow", 0, 0, (void*)FL_YELLOW);
  color->value(0);
  
  // Output display
  output = new Fl_Box(50, 160, 300, 100);
  output->box(FL_DOWN_BOX);
  output->label("Select an option");
  
  win->end();
  win->show();
  return Fl::run();
}

Advanced Usage

Submenu Support

Like other menu widgets, Fl_Choice supports submenus:

Fl_Choice *choice = new Fl_Choice(100, 50, 200, 25, "Font:");

// Add items with pathname notation
choice->add("Sans Serif/Helvetica");
choice->add("Sans Serif/Arial");
choice->add("Serif/Times");
choice->add("Serif/Palatino");
choice->add("Monospace/Courier");
choice->add("Monospace/Monaco");

choice->value(0);

Programmatic Selection

// Select by index
choice->value(2);

// Select by label
int index = choice->find_index("Medium");
if (index >= 0) {
  choice->value(index);
}

// Select by menu item pointer
const Fl_Menu_Item *item = choice->find_item("Large");
if (item) {
  choice->value(item);
}

Getting Selection Information

// Get selected index
int idx = choice->value();  // -1 if none selected

// Get selected label
const char *label = choice->text();

// Get selected menu item
const Fl_Menu_Item *item = choice->mvalue();
if (item) {
  void *userdata = item->user_data();
  long argument = item->argument();
  int shortcut = item->shortcut();
}

Common Patterns

Font Selector

Fl_Choice *font_choice = new Fl_Choice(100, 50, 150, 25, "Font:");
font_choice->add("Helvetica");
font_choice->add("Helvetica Bold");
font_choice->add("Helvetica Italic");
font_choice->add("Times");
font_choice->add("Times Bold");
font_choice->add("Courier");
font_choice->value(0);

Size Selector

Fl_Choice *size_choice = new Fl_Choice(100, 90, 150, 25, "Size:");
size_choice->add("8");
size_choice->add("10");
size_choice->add("12");
size_choice->add("14");
size_choice->add("18");
size_choice->add("24");
size_choice->value(2);  // Select "12"

Enum-Based Selection

enum ChartType {
  BAR_CHART = 0,
  LINE_CHART = 1,
  PIE_CHART = 2
};

Fl_Choice *chart = new Fl_Choice(100, 130, 150, 25, "Chart:");
chart->add("Bar",  0, 0, (void*)BAR_CHART);
chart->add("Line", 0, 0, (void*)LINE_CHART);
chart->add("Pie",  0, 0, (void*)PIE_CHART);

void chart_cb(Fl_Widget *w, void*) {
  Fl_Choice *c = (Fl_Choice*)w;
  ChartType type = (ChartType)c->mvalue()->argument();
  update_chart(type);
}

Core Classes

Basic Widgets

Menu Widgets

Container Widgets

Complex Widgets

Drawing & Graphics

Documentation Index

​Fl_Choice

​Header

​Inheritance

​Constructor

​Fl_Choice()

​Overview

​Adding Choices

​Using add()

​Simple Example

​Using Static Array

​With User Data

​Value Methods

​value()

​text()

​mvalue()

​prev_mvalue()

​Callbacks

​Widget Callback

​Item Callbacks

​Change Detection

​changed()

​Mouse Button Behavior

​Events

​FL_BEFORE_MENU Event

​Appearance

​down_box()

​Text Appearance

​Box and Color

​Managing Items

​Finding Items

​Modifying Items

​Removing Items

​Item Count

​Complete Example

​Advanced Usage

​Submenu Support

​Programmatic Selection

​Getting Selection Information

​Common Patterns

​Font Selector

​Size Selector

​Enum-Based Selection

​See Also

Fl_Choice

Header

Inheritance

Constructor

Fl_Choice()

Overview

Adding Choices

Using add()

Simple Example

Using Static Array

With User Data

Value Methods

value()

text()

mvalue()

prev_mvalue()

Callbacks

Widget Callback

Item Callbacks

Change Detection

changed()

Mouse Button Behavior

Events

FL_BEFORE_MENU Event

Appearance

down_box()

Text Appearance

Box and Color

Managing Items

Finding Items

Modifying Items

Removing Items

Item Count

Complete Example

Advanced Usage

Submenu Support

Programmatic Selection

Getting Selection Information

Common Patterns

Font Selector

Size Selector

Enum-Based Selection

See Also