How to write an easy to test robot program
The command based programming model is designed to simplify creating very easy to write and especially easy to test robot programs. All the pieces come together when it's time to see how your program works so that pieces developed by multiple programmers can be integrated and tested with the main robot program.
Break up the robot into subsystems
Create commands for each robot behavior
Commands define the behaviors of the robot, that is the operation of the subsystems over time. A command starts a subsystem doing something, then waits until it is finished. Upon completion, the next command can be scheduled. It is the defining of commands for each behavior that is the key to making it easy to test the code as you'll see in the next few sections of this lesson.
Add commands to the SmartDashboard
Test commands indivudually using the SmartDashboard
When a command is added to the SmartDashboard a button is created on the screen that will, when pressed, schedule the command to run. By doing this you can easily test each command individually to make sure it works. This is a key principle in programming, that is unit test each part of the larger program separately, then you'll have confidence that putting the units (commands) together into a larger program will also work.
Adding commands to the SmartDashboard using RobotBuilder
The idea of adding commands to testing pieces of your robot program individually is so useful that a checkbox was added to RobotBuilder to automatically generate SmartDashboard buttons. Just check the box for any command and it will automatically appear as a button that, when pressed, will run the command.
Test commands indivudually using a joystick button
In addition to testing commands using the SmartDashboard, you can also "wire" commands to joystick buttons. This is another easy way to verify that commands work as you expect. And, in fact, in your finished robot program, you will likely have a number of commands wired to many of the joystick buttons as a way of controlling the robot.
In this example there is a command called ScoreATube that presumably places a scoring object somewhere. Then there is a JoystickButton object called TubeScoringButton that has as its command the ScoreATube command. When the button is pressed, the command will run.
Combine simple commands into Command Groups
Once individual commands are working, they can be combined into Command Groups. Command Groups are commands that each consist of a list of commands to run when scheduled. This is where much of the power of the system comes into play. Suppose the robot needs to score an inner tube by driving forward for some distance, spinning rollers to release the tube for 1 second, moving a wrist joint, and backing up the robot. If there are commands for each of those operations, the can be individually tested, then a command group just lists all the individual commands, and the group is tied to a button. When the button is pressed, all the individual commands in the group run sequentially. Commands can even be scheduled to run in parallel for operations that can happen simultaneously.
Add robot status to the SmartDashboard
Often you want to see the status of the robot by displaying values on the driver station. In the past this was handled with adding lots of print statements to the program and values poured out of the program, usually so fast that it was hard to know what was going on. With the SmartDashboard, you can create a display just by sending values, and they will automatically be displayed in the graphical user interface. In fact, you can change the format of the fields to more appropriate displays. For example, for a gyro, its heading can be displayed as a compass.
In addition display "widgets" or graphical elements can be created as standard Java code and added to the dashboard to make custom dashboards easily by programmers. For more detail see the section on the SmartDashboard.