# The new Form, FormField auto-validation API

> Gives more control in how to auto validate a Form and a FormField.




:::important
These breaking change docs are accurate, as of the release
under which they are published. Over time, the
workarounds described here might become inaccurate.
We don't, in general, keep these breaking change docs up
to date as of each release.

这些破坏性改动文档的准确性仅限于其发布时对应的版本。
随着时间的推移，文档中描述的方案可能会逐渐失效。
通常情况下，我们不会在每次发布新版本时都对这些文档进行同步更新。

The [breaking change index file](/release/breaking-changes)
lists the docs created for each release.

[破坏性改动列表](/release/breaking-changes) 
列出了每个版本的文档。

:::


## Summary

The previous auto validation API for the `Form` and
`FormField` widgets didn't control when auto validation
should occur. So the auto validation for these widgets
always happened on first build when the widget was first
visible to the user, and you weren't able to control
when the auto validation should happen.

## Context

Due to the original API not allowing developers to change
the auto validation behavior for validating only when
the user interacts with the form field, we added new API
that allows developers to configure how they want
auto validation to behave for the `Form` and `FormField`
widgets.

## Description of change

The following changes were made:

* The `autovalidate` parameter is deprecated.
* A new parameter called `autovalidateMode`,
  an Enum that accepts values from the `AutovalidateMode`
  Enum class, is added.

## Migration guide

To migrate to the new auto validation API you need to
replace the usage of the deprecated `autovalidate`
parameter to the new `autovalidateMode` parameter.
If you want the same behavior as before you can use:
`autovalidateMode = AutovalidateMode.always`.
This makes your `Form` and `FormField` widgets auto
validate on first build and every time it changes.

Code before migration:

```dart
class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FormField(
      autovalidate: true,
      builder: (FormFieldState state) {
        return Container();
      },
    );
  }
}
```

Code after migration:

```dart
class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FormField(
      autovalidateMode: AutovalidateMode.always,
      builder: (FormFieldState state) {
        return Container();
      },
    );
  }
}
```

## Timeline

Landed in version: 1.21.0-5.0.pre<br>
In stable release: 1.22

## References

API documentation:

* [`AutovalidateMode`](https://api.flutter-io.cn/flutter/widgets/AutovalidateMode.html)

Relevant issues:

* [Issue 56363](https://github.com/flutter/flutter/issues/56363)
* [Issue 18885](https://github.com/flutter/flutter/issues/18885)
* [Issue 15404](https://github.com/flutter/flutter/issues/15404)
* [Issue 36154](https://github.com/flutter/flutter/issues/36154)
* [Issue 48876](https://github.com/flutter/flutter/issues/48876)

Relevant PRs:

* [PR 56365: FormField should autovalidate only if its
  content was changed](https://github.com/flutter/flutter/pull/56365)
* [PR 59766: FormField should autovalidate only if its
  content was changed (fixed)](https://github.com/flutter/flutter/pull/59766)