markdown 当Field更新时，Formik会更新其他值

Posted 2021-05-05

use onChange, values and setFieldValue  
exp: when amount changed, get quantity from values and calculate total
```jsx
<Field type="number" name='amount'
  onChange={(e: any) => {
    const amount = e.target.value
    const quantity = values.quantity;
    setFieldValue('amount', amount, true)
    setFieldValue('total', amount * quantity, true)
  }}
/>
```