Storybook: Forms.Form docs (#22654)

* Add Select error message

* Update Form docs

* Tweak examples

* Fix docs

packages/grafana-ui/src/components/Forms/Form.mdx

@@ -25,7 +25,7 @@ const defaultUser: Partial<UserDTO> = {
 
 <Forms.Form
   defaultValues={defaultUser}
-  onSubmit={async (user: UserDTO) => await createrUser(user)}
+  onSubmit={async (user: UserDTO) => await createUser(user)}
 >{({register, errors}) => {
   return (
     <Forms.Field>
@@ -64,17 +64,19 @@ Register accepts an object which describes validation rules for a given input:
 
 #### `errors`
 
-`errors` in an object that contains validation errors of the form. To show error message and invalid input indication in your form, wrap input element with `<Forms.Field ...>` component and pass `invalid` and `error` props to it:
+`errors` is an object that contains validation errors of the form. To show error message and invalid input indication in your form, wrap input element with `<Forms.Field ...>` component and pass `invalid` and `error` props to it:
 
 ```jsx
-<Forms.Field label="Name" invalid={!!errors.name} error={!!errors.name && 'Name is required'}>
+<Forms.Field label="Name" invalid={!!errors.name} error='Name is required'>
   <Forms.Input name="name" ref={register({ required: true })} />
 </Forms.Field>
 ```
 
 #### `control`
 
-By default `Form` component assumes form elements are uncontrolled (https://reactjs.org/docs/glossary.html#controlled-vs-uncontrolled-components). There are some components like `RadioButton` or `Select` that are controlled-only and require some extra work. To make them work with the form, you need to render those using `Forms.InputControl` component:
+By default `Form` component assumes form elements are uncontrolled (https://reactjs.org/docs/glossary.html#controlled-vs-uncontrolled-components).
+There are some components like `RadioButton` or `Select` that are controlled-only and require some extra work. To make
+them work with the form, you need to render those using `Forms.InputControl` component:
 
 ```jsx
 import { Forms } from '@grafana/ui';
@@ -106,11 +108,41 @@ import { Forms } from '@grafana/ui';
   </>
 )}
 </Forms.Form>
+```
+Note that when using `Forms.InputControl`, it expects the name of the prop that handles input change to be called `onChange`.
+If the property is named differently for any specific component, additional `onChangeName` prop has to be provided, specifying the name.
+Additionally, the `onChange` arguments passed as an array. Check [react-hook-form docs](https://react-hook-form.com/api/#Controller)
+for more prop options.
+
+```jsx
+{/* DashboardPicker has onSelected prop instead of onChange */}
+import { DashboardPicker } from 'app/core/components/Select/DashboardPicker';
+
+{/* In case of Select the value has to be returned as an object with a `value` key for the value to be saved to form data */}
+const onSelectChange = ([value]) => {
+  // ...
+  return { value };
+}
+
+<Field label="SelectExample">
+  <Forms.InputControl
+    as={DashboardPicker}
+    control={control}
+    name="select"
+    onSelected={onSelectChange}
+    {/* Pass the name of the onChange handler */}
+    onChangeName='onSelected'
+  />
+</Field>
+
 ```
 
 ### Default values
 
-Default values of the form can be passed either via `defaultValues` property on the `Form` element, or directly on form's input via `defaultValue` prop:
+Default values of the form can be passed either via `defaultValues` property on the `Form` element, or directly on
+form's input via `defaultValue` prop.
+Note that changing/updating `defaultValues` passed to the form will reset the form's state, which might be undesirable in
+case it has both controlled and uncontrolled components. In that case it's better to pass `defaultValue` to each form component separately.
 
 ```jsx
 // Passing default values to the Form

packages/grafana-ui/src/components/Forms/Form.story.tsx

@@ -98,7 +98,7 @@ const renderForm = (defaultValues?: Partial<FormDTO>) => (
             <Forms.InputControl name="radio" control={control} options={selectOptions} as={RadioButtonGroup} />
           </Field>
 
-          <Field label="Select" invalid={!!errors.select}>
+          <Field label="Select" invalid={!!errors.select} error="Select is required">
             <Forms.InputControl
               name="select"
               control={control}

packages/grafana-ui/src/components/Forms/Form.tsx

@@ -10,9 +10,9 @@ interface FormProps<T> {
   children: (api: FormAPI<T>) => React.ReactNode;
 }
 
-export function Form<T>({ validateOn, defaultValues, onSubmit, children }: FormProps<T>) {
+export function Form<T>({ defaultValues, onSubmit, children, validateOn = 'onSubmit' }: FormProps<T>) {
   const { handleSubmit, register, errors, control, reset, getValues } = useForm<T>({
-    mode: validateOn || 'onSubmit',
+    mode: validateOn,
     defaultValues,
   });