RetryCommand

Overview

RetryCommand is a powerful command for building robust and adaptable command sequences. It runs a command and, if a specified condition isn’t met upon completion, automatically retries it—either by re-running the same command or switching to a different one—up to a defined number of times.

This is especially useful for actions that may fail on the first attempt, such as vision-based alignment, object grabbing, or precise mechanism positioning.

This command is available in both SolversLib and NextFTC (separate packages).

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Usage

Setup

To use RetryCommand, you need to provide the constructor with:

• The command to run – the initial action you want to execute.

• (Optional) A different command to run on retries – lets you customize the retry behavior per attempt (e.g., switching to a vision-assisted command if the initial attempt fails).

• A retry condition – a function that checks whether the action was successful. If this condition returns true, the command will be retried.

• The maximum number of retries – defines the maximum number of times the command can be retried.

new RetryCommand(
    new GrabCommand(claw),   // Command to run.
    () -> !claw.isGrabbed(), // If this condition is true
    5                        // retry up to 5 times.
)

Or with custom retry logic:

new RetryCommand(
    new GrabCommand(claw),                  // Command to run initially.
    new DetectAndGrabCommand(claw, vision), // Command to run on each retry.
    () -> !claw.isGrabbed(),                // If this condition is true
    5                                       // retry up to 5 times.
)

Example Usage

The following is an example autonomous program that showcases RetryCommand's functionality, using SolversLib's command system:

This is by no means a functional autonomous program.

public class MyAuto extends CommandOpMode {
    private ClawSubsystem clawSubsystem;
    private VisionSubsystem visionSubsystem;

    @Override
    public void initialize() {
        clawSubsystem = new ClawSubsystem(hardwareMap);
        visionSubsystem = new VisionSubsystem(hardwareMap);

        schedule(
            new SequentialCommandGroup(
                // First, try to grab. If unsuccessful, retry grabbing up to 3 times.
                new RetryCommand(
                    new GrabCommand(clawSubsystem),
                    () -> !clawSubsystem.isHoldingGameElement(),
                    3
                ),
                
                // ---- OR ----
                
                // First, try to grab. If unsuccessful, try to detect and grab using vision up to 3 times.
                new RetryCommand(
                    new GrabCommand(clawSubsystem),
                    new DetectAndGrabCommand(clawSubsystem, visionSubsystem), 
                    () -> !clawSubsystem.isHoldingGameElement(),
                    3
                )
            )
        );
    }
}

Source Code

You can check out the source code on the GitHub repository.

If you are using an unsupported command-based library and want to implement this command in your codebase, you may do so.