Material UI + React Form Hook + multiple checkboxes + default selected

Here's my solution, which is not using all the default components from Material UI cause at my interface each radio will have an icon and text, besides the default bullet point not be showed:

const COMPANY = "company";

const INDIVIDUAL = "individual";

const [scope, setScope] = useState(context.scope || COMPANY);

const handleChange = (event) => {
  event.preventDefault();

  setScope(event.target.value);
};

<Controller
  as={
    <FormControl component="fieldset">
      <RadioGroup
        aria-label="scope"
        name="scope"
        value={scope}
        onChange={handleChange}
      >
        <FormLabel>
          {/* Icon from MUI */}
          <Business />

          <Radio value={COMPANY} />

          <Typography variant="body1">Company</Typography>
        </FormLabel>

        <FormLabel>
          {/* Icon from MUI */}
          <Personal />

          <Radio value={INDIVIDUAL} />

          <Typography variant="body1">Individual</Typography>
        </FormLabel>
      </RadioGroup>
    </FormControl>
  }
  name="scope"
  control={methods.control}
/>;

Observation: At this example I use React Hook Form without destruct:

const methods = useForm({...})

I've been struggling with this as well, here is what worked for me.

Updated solution for react-hook-form v6, it can also be done without useState(sandbox link below):

import React, { useState } from "react";
import { useForm, Controller } from "react-hook-form";
import FormControlLabel from "@material-ui/core/FormControlLabel";
import Checkbox from "@material-ui/core/Checkbox";

export default function CheckboxesGroup() {
  const defaultNames = ["bill", "Manos"];
  const { control, handleSubmit } = useForm({
    defaultValues: { names: defaultNames }
  });

  const [checkedValues, setCheckedValues] = useState(defaultNames);

  function handleSelect(checkedName) {
    const newNames = checkedValues?.includes(checkedName)
      ? checkedValues?.filter(name => name !== checkedName)
      : [...(checkedValues ?? []), checkedName];
    setCheckedValues(newNames);

    return newNames;
  }

  return (
    <form onSubmit={handleSubmit(data => console.log(data))}>
      {["bill", "luo", "Manos", "user120242"].map(name => (
        <FormControlLabel
          control={
            <Controller
              name="names"
              render={({ onChange: onCheckChange }) => {
                return (
                  <Checkbox
                    checked={checkedValues.includes(name)}
                    onChange={() => onCheckChange(handleSelect(name))}
                  />
                );
              }}
              control={control}
            />
          }
          key={name}
          label={name}
        />
      ))}
      <button>Submit</button>
    </form>
  );
}

Codesandbox link: https://codesandbox.io/s/material-demo-54nvi?file=/demo.js

Another solution with default selected items done without useState: https://codesandbox.io/s/material-demo-bzj4i?file=/demo.js

Here is a working version:

import React from "react";
import { useForm, Controller } from "react-hook-form";
import FormControlLabel from "@material-ui/core/FormControlLabel";
import Checkbox from "@material-ui/core/Checkbox";

export default function CheckboxesGroup() {
  const { control, handleSubmit } = useForm({
    defaultValues: {
      bill: "bill",
      luo: ""
    }
  });

  return (
    <form onSubmit={handleSubmit(e => console.log(e))}>
      {["bill", "luo"].map(name => (
        <Controller
          key={name}
          name={name}
          as={
            <FormControlLabel
              control={<Checkbox value={name} />}
              label={name}
            />
          }
          valueName="checked"
          type="checkbox"
          onChange={([e]) => {
            return e.target.checked ? e.target.value : "";
          }}
          control={control}
        />
      ))}
      <button>Submit</button>
    </form>
  );
}

codesandbox link: https://codesandbox.io/s/material-demo-65rjy?file=/demo.js:0-932

However, I do not recommend doing so, because Checkbox in material UI probably should return checked (boolean) instead of (value).

Breaking API changes made in 6.X:

• validation option has been changed to use a resolver function wrapper and a different configuration property name
  Note: Docs were just fixed for validationResolver->resolver, and code examples for validation in repo haven't been updated yet (still uses validationSchema for tests). It feels as if they aren't sure what they want to do with the code there, and it is in a state of limbo. I would avoid their Controller entirely until it settles down, or use Controller as a thin wrapper for your own form Controller HOC, which appears to be the direction they want to go in.
  see official sandbox demo and the unexpected behavior of "false" value as a string of the Checkbox for reference

import { yupResolver } from "@hookform/resolvers";

  const { register, handleSubmit, control, getValues, setValue } = useForm({
    resolver: yupResolver(schema),
    defaultValues: Object.fromEntries(
      boats.map((boat, i) => [
        `boat_ids[${i}]`,
        preselectedBoats.some(p => p.id === boats[i].id)
      ])
    )
  });

• Controller no longer handles Checkbox natively (type="checkbox"), or to better put it, handles values incorrectly. It does not detect boolean values for checkboxes, and tries to cast it to a string value. You have a few choices:

1. Don't use Controller. Use uncontrolled inputs
2. Use the new render prop to use a custom render function for your Checkbox and add a setValue hook
3. Use Controller like a form controller HOC and control all the inputs manually

Examples avoiding the use of Controller:
https://codesandbox.io/s/optimistic-paper-h39lq
https://codesandbox.io/s/silent-mountain-wdiov
Same as first original example but using yupResolver wrapper

---

Description for 5.X:

Here is a simplified example that doesn't require Controller. Uncontrolled is the recommendation in the docs. It is still recommended that you give each input its own name and transform/filter on the data to remove unchecked values, such as with yup and validatorSchema in the latter example, but for the purpose of your example, using the same name causes the values to be added to an array that fits your requirements.
https://codesandbox.io/s/practical-dijkstra-f1yox

Anyways, the problem is that your defaultValues doesn't match the structure of your checkboxes. It should be {[name]: boolean}, where names as generated is the literal string boat_ids[${boat.id}], until it passes through the uncontrolled form inputs which bunch up the values into one array. eg: form_input1[0] form_input1[1] emits form_input1 == [value1, value2]

https://codesandbox.io/s/determined-paper-qb0lf

Builds defaultValues: { "boat_ids[0]": false, "boat_ids[1]": true ... }
Controller expects boolean values for toggling checkbox values and as the default values it will feed to the checkboxes.

 const { register, handleSubmit, control, getValues, setValue } = useForm({
    validationSchema: schema,
    defaultValues: Object.fromEntries(
      preselectedBoats.map(boat => [`boat_ids[${boat.id}]`, true])
    )
  });

Schema used for the validationSchema, that verifies there are at least 2 chosen as well as transforms the data to the desired schema before sending it to onSubmit. It filters out false values, so you get an array of string ids:

  const schema = Yup.object().shape({
    boat_ids: Yup.array()
      .transform(function(o, obj) {
        return Object.keys(obj).filter(k => obj[k]);
      })
      .min(2, "")
  });