Button#

Introduction #

The button class is a derived class of the controller class. It provides access to controller button states and button event callbacks.

A button object is accessed through a controller object. It is not constructed directly.

The IQ (1st gen) Controller has eight main button objects. If an IQ (2nd gen) Controller is connected to the IQ (1st gen) Brain, the joystick buttons ButtonL3 and ButtonR3 can also be used.

Access #

The controller class provides the following button objects. Each object is an instance of the button class.

Object	Example Usage	Description
`ButtonEDown`	`Controller.ButtonEDown.pressing()`	The E ▼ button.
`ButtonEUp`	`Controller.ButtonEUp.pressing()`	The E ▲ button.
`ButtonFDown`	`Controller.ButtonFDown.pressing()`	The F ▼ button.
`ButtonFUp`	`Controller.ButtonFUp.pressing()`	The F ▲ button.
`ButtonLDown`	`Controller.ButtonLDown.pressing()`	The L ▼ button.
`ButtonLUp`	`Controller.ButtonLUp.pressing()`	The L ▲ button.
`ButtonRDown`	`Controller.ButtonRDown.pressing()`	The R ▼ button.
`ButtonRUp`	`Controller.ButtonRUp.pressing()`	The R ▲ button.
`ButtonL3`	`Controller.ButtonL3.pressing()`	The Left Joystick button. IQ (2nd gen) Controller only.
`ButtonR3`	`Controller.ButtonR3.pressing()`	The Right Joystick button. IQ (2nd gen) Controller only.

Notes #

Before using a button member function, create a controller object.
ButtonL3 and ButtonR3 are only available when an IQ (2nd gen) Controller is connected.

// Create a controller object
controller Controller = controller();

Member Functions #

The button class includes the following member functions:

Getter — Read button state.

pressing — Returns whether the button is being pressed.

Callbacks — Run functions when button events occur.

pressed — Registers a function to run when the button is pressed.
released — Registers a function to run when the button is released.

Getter #

pressing #

pressing returns whether the button is currently being pressed.

Available Function

bool pressing() const;

Parameters

This function does not have parameters.

Return Value

Returns a Boolean value.

true — The button is being pressed.
false — The button is not being pressed.

Example

// Turn right while R Up is pressed
while (true) {
  if (Controller.ButtonRUp.pressing()) {
    Drivetrain.turn(right);
  }
  else {
    Drivetrain.stop();
  }

  wait(20, msec);
}

Callbacks #

pressed #

pressed registers a function that runs when the button is pressed.

Available Function

void pressed(void (* callback)(void)) const;

Parameter	Type	Description
`callback`	`void (*)(void)`	A function that runs when the button is pressed.

Return Value

This function does not return a value.

Example

Define the callback function outside of main.

// Drive forward when F Up is pressed
void driveForward() {
  Drivetrain.driveFor(forward, 100, mm);
}

int main() {
  vexcodeInit();

  // Run driveForward when F Up is pressed
  Controller.ButtonFUp.pressed(driveForward);
}

released #

released registers a function that runs when the button is released.

Available Function

void released(void (* callback)(void)) const;

Parameter	Type	Description
`callback`	`void (*)(void)`	A function that runs when the button is released.

Return Value

This function does not return a value.

Example

Define the callback function outside of main.

// Stop the drivetrain when F Up is released
void stopDriving() {
  Drivetrain.stop();
}

int main() {
  vexcodeInit();

  // Run stopDriving when F Up is released
  Controller.ButtonFUp.released(stopDriving);
}