Fluid Constants

FluidConstants are 'constant' values initially declared at compile-time which can be updated over network tables at run-time. This is useful for values which you may want to change quickly without needing to re-deploy or SSH into your robot. The FluidConstant class implements the Supplier<T> interface to allow abstraction to a supplier in cases where you only retrieve the current value. If your use case matches that, cast the variable to a Supplier so if anything about this class changes, your code will not break!

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Make a new FluidConstant

Creates a new FluidConstant of type String with the name network-table-name and initial value initialValue

FluidConstant<String> myFluidConstant = new FluidConstant<>("network-table-name", "initialValue");

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Register the FluidConstant to a NetworkTable

NetworkTable constantsTable = NetworkTableInstance.getDefault().getTable("constants");
myFluidConstant.registerToTable(constantsTable);

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Get or set the value of a FluidConstant (on the robot)

String value = myFluidConstant.getValue();               // Gets the current value
String initialValue = myFluidConstant.getInitialValue(); // Gets the value as defined at compile-time
myFluidConstant.setValue("New value");                   // Set the current value

- OR -
If you only plan on retreiving the values use this instead:

// Cast the fluid constant to a Supplier. This make your code unbreakable because Supplier will never change, but FluidConstant might!
Supplier<String> myFluidConstantSupplier = myFluidConstant;
myFluidConstantSupplier.get();

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Get or set the value of a FluidConstant (Over network tables)

You can use any method of listing and modifying NetworkTables for this. If you have no idea what those are, you can use the FRC Outline Viewer that comes bundled with WPILib.

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Register an action to run when the value is updated

The parameter to this method accepts a BiConsumer. It is an anonymous 'lambda' function that can either be declared in-line with the rest of the code or as a method which accepts 2 arguments (Both the same as your constant type).

myFluidConstant.registerListener((oldVal, newVal) -> {
   // Your code here
});

- OR -

private void onUpdate(String oldVal, String newVal) {
    // Your code here
}

// ...
myFluidConstant.registerListener(this::onUpdate);

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Chainable methods

Both the registerToTable and registerListener methods return the instance of FluidConstant<T> to allow chaining them after the initial declaration.

So instead of:

NetworkTable constantsTable = NetworkTableInstance.getDefault().getTable("constants");
FluidConstant<Double> fcDouble = new FluidConstant<>("fc-double", 0d);
fcDouble.registerToTable(constantsTable);
fcDouble.registerListener(this::fcDoubleUpdated);

You can instead do:

NetworkTable constantsTable = NetworkTableInstance.getDefault().getTable("constants");
FluidConstant<Double> fcDouble = new FluidConstant<>("fc-double", 0d)
                      .registerToTable(constantsTable)
                      .registerListener(this::fcDoubleUpdated); 

This makes your code more readable and more organized.