Commands
Overview
Commands define robot actions. They use subsystem methods to perform tasks. Commands can be full classes or inline factories for simple actions.
Command Lifecycle
Four key methods:
- initialize(): Called once when command starts.
- execute(): Called every loop (20ms) while scheduled.
- isFinished(): Returns true when command should end.
- end(interrupted): Called once when command ends or is interrupted.
Full Command Class
For complex commands, create a class extending Command. Always call addRequirements() in the constructor to declare which subsystems the command uses.
Full Command Example
package frc.robot.commands;
import edu.wpi.first.wpilibj2.command.Command;
import frc.robot.subsystems.Intake;
public class RunIntakeCommand extends Command {
private final Intake m_intake;
public RunIntakeCommand(Intake intake) {
m_intake = intake;
addRequirements(intake);
}
@Override
public void initialize() {
m_intake.run(0.6);
}
@Override
public void end(boolean interrupted) {
m_intake.stop();
}
}Inline Commands
For simple actions, use command constructors like new RunCommand() or new InstantCommand(). These reduce boilerplate for straightforward tasks.
Inline Command Examples
import edu.wpi.first.wpilibj2.command.Command;
import edu.wpi.first.wpilibj2.command.InstantCommand;
import edu.wpi.first.wpilibj2.command.RunCommand;
import frc.robot.subsystems.Intake;
// Run continuously while scheduled
Command runCmd = new RunCommand(() -> intake.run(0.6), intake);
// Run once immediately, then finish
Command stopCmd = new InstantCommand(() -> intake.stop(), intake);
// Run with a condition
Command conditionalCmd = new RunCommand(() -> intake.run(0.6), intake)
.until(() -> intake.hasGamePiece());Requirements
Commands declare subsystem requirements to prevent conflicts. The Scheduler ensures only one command controls a subsystem at a time. If a new command requires a subsystem in use, it interrupts the current command.