Fix <FormDataConsumer> causes its children to flicker

packages/ra-core/src/form/FormDataConsumer.tsx

@@ -4,6 +4,7 @@ import { useFormContext, FieldValues } from 'react-hook-form';
 import get from 'lodash/get';
 import { useFormValues } from './useFormValues';
 import { useWrappedSource } from '../core';
+import { useEvent } from '../util';
 
 /**
  * Get the current (edited) value of the record from the form and pass it
@@ -67,22 +68,26 @@ export const FormDataConsumerView = <
     props: Props<TFieldValues>
 ) => {
     const { children, formData, source } = props;
-    let ret;
+    const [result, setResult] = React.useState<ReactNode>(null);
 
     const finalSource = useWrappedSource(source || '');
+    const render = useEvent(children);
 
-    // Passes an empty string here as we don't have the children sources and we just want to know if we are in an iterator
-    const matches = ArraySourceRegex.exec(finalSource);
+    // Getting the result of the children function in a useEffect allows us to keep a stable reference to is
+    // with useEvent
+    React.useEffect(() => {
+        // Passes an empty string here as we don't have the children sources and we just want to know if we are in an iterator
+        const matches = ArraySourceRegex.exec(finalSource);
+        // If we have an index, we are in an iterator like component (such as the SimpleFormIterator)
+        if (matches) {
+            const scopedFormData = get(formData, matches[0]);
+            setResult(render({ formData, scopedFormData }));
+        } else {
+            setResult(render({ formData }));
+        }
+    }, [finalSource, formData, render]);
 
-    // If we have an index, we are in an iterator like component (such as the SimpleFormIterator)
-    if (matches) {
-        const scopedFormData = get(formData, matches[0]);
-        ret = children({ formData, scopedFormData });
-    } else {
-        ret = children({ formData });
-    }
-
-    return ret === undefined ? null : ret;
+    return result;
 };
 
 const ArraySourceRegex = new RegExp(/.+\.\d+$/);

packages/ra-ui-materialui/src/form/FormDataConsumer.stories.tsx

@@ -0,0 +1,95 @@
+import * as React from 'react';
+import { FormDataConsumer, required, ResourceContextProvider } from 'ra-core';
+import fakeRestDataProvider from 'ra-data-fakerest';
+import { AdminContext } from '../AdminContext';
+import { AutocompleteInput, ReferenceInput, TextInput } from '../input';
+import { SimpleForm } from './SimpleForm';
+import { Create } from '../detail';
+
+// We keep this test in ra-ui-materialui because we need heavy components to reproduce the issue https://github.com/marmelab/react-admin/issues/10415
+export default { title: 'ra-core/form/FormDataConsumer' };
+
+export const Basic = () => (
+    <AdminContext dataProvider={dataProvider}>
+        <ResourceContextProvider value="posts">
+            <Create>
+                <SimpleForm>
+                    <TextInput source="title" />
+                    <FormDataConsumer<any>>
+                        {({ formData }) => {
+                            console.log({ formData });
+                            if (!formData.title) {
+                                return null;
+                            }
+                            return (
+                                <ReferenceInput
+                                    source="userId"
+                                    reference="users"
+                                >
+                                    <AutocompleteInput
+                                        shouldUnregister
+                                        label="User"
+                                        optionText={choice =>
+                                            `${choice.name} / (${choice.id})`
+                                        }
+                                        noOptionsText="User doesn't exist"
+                                        isRequired
+                                        validate={[
+                                            required('User is required.'),
+                                        ]}
+                                    />
+                                </ReferenceInput>
+                            );
+                        }}
+                    </FormDataConsumer>
+                    <TextInput source="body" multiline rows={5} />
+                </SimpleForm>
+            </Create>
+        </ResourceContextProvider>
+    </AdminContext>
+);
+
+const dataProvider = fakeRestDataProvider({
+    users: [
+        {
+            id: 1,
+            name: 'Leanne Graham',
+        },
+        {
+            id: 2,
+            name: 'Ervin Howell',
+        },
+        {
+            id: 3,
+            name: 'Clementine Bauch',
+        },
+        {
+            id: 4,
+            name: 'Patricia Lebsack',
+        },
+        {
+            id: 5,
+            name: 'Chelsey Dietrich',
+        },
+        {
+            id: 6,
+            name: 'Mrs. Dennis Schulist',
+        },
+        {
+            id: 7,
+            name: 'Kurtis Weissnat',
+        },
+        {
+            id: 8,
+            name: 'Nicholas Runolfsdottir V',
+        },
+        {
+            id: 9,
+            name: 'Glenna Reichert',
+        },
+        {
+            id: 10,
+            name: 'Clementina DuBuque',
+        },
+    ],
+});