< 1511 Teaching Resources

Calculator

In this lab, you will create a primitive calculator using a <ps4, Xbox> controller.

Prelab question:

  1. How do you initialize a controller?

Lab:

It’s time to learn about Trigger Binding. You’ve learned how to check if a Trigger is being triggered, but now you need to do something when the Trigger is triggered. You first need to write a function that will execute some code. Let’s call our function coolFunc.

void coolFunc() { 
	SmartDashboard.putString(“Cool String”, “Hello”); 
}

Ok, now, how do we call it? Let’s first create a controller object, called driverController. This object has many methods, but we mainly care about the buttons, which are simple.

driverController.b() is used to query the b button being held. However, you’ll notice it doesn’t return a bool, it returns a Trigger. This is very convenient, because Triggers have some methods that let us use these things called Commands. Commands are the essential part of running a robot. We need to create a Command using our function, coolFunc. The easiest way to do this is through something called an InstantCommand.

InstantCommand coolCommand = new InstantCommand(coolFunc);

This runs whatever function you pass in (in this case, coolFunc) and executes it instantly. However, there is another way you can create InstantCommands that helps our situation better. It looks kinda wack though.

new InstantCommand(() -> coolFunc());

(We’ll learn this syntax later)

You can then throw this into one of our Trigger’s methods like so:

driverController.b().onTrue(new InstantCommand(()->coolFunc()));

We’ll do this in our RobotContainer.java, in configureBindings. This will bind the Command that runs our function, coolFunc to the start of the b button being held. There are a lot of methods similar to Trigger.onTrue to be used for any need. You can see Trigger documentation here.

Now for the hard part.

Your task:

Create a basic calculator that allows for basic input using buttons on a controller. You can use any buttons you want, but the base functionality you need is:

Test your program! Does it work? Raise your hand if you need help.