# GestureRecognizer cleanup

> OneSequenceGestureRecognizer subclasses should override `addAllowedPointer` to take a `PointerDownEvent`




:::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.

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


## Summary

`OneSequenceGestureRecognizer.addAllowedPointer()` was changed to take a
`PointerDownEvent`, like its superclass. Previously, it accepted the more
general `PointerEvent` type, which was incorrect.

## Context

The framework only ever passes `PointerDownEvent` objects to
`addAllowedPointer()`. Declaring
`OneSequenceGestureRecognizer.addAllowedPointer()` to take the more general
type was confusing, and caused `OneSequenceGestureRecognizer` subclasses to
have to cast their argument to the right class.

## Description of change

The previous declaration forced `OneSequenceGestureRecognizer` descendants to
override `addAllowedPointer()` like so:

```dart
class CustomGestureRecognizer extends ScaleGestureRecognizer {
  @override
  void addAllowedPointer(PointerEvent event) {
    // insert custom handling of event here...
    super.addAllowedPointer(event);
  }
}
```

The new method declaration will cause this code to fail with the following
error message:

```plaintext
super.addAllowedPointer(event); The argument type 'PointerEvent' can't be assigned to the parameter type 'PointerDownEvent'.
                                #argument_type_not_assignable

```

## Migration guide

Code before migration:

```dart
class CustomGestureRecognizer extends ScaleGestureRecognizer {
  @override
  void addAllowedPointer(PointerEvent event) {
    // insert custom handling of event here...
    super.addAllowedPointer(event);
  }
}
```

Code after migration:

```dart
class CustomGestureRecognizer extends ScaleGestureRecognizer {
  @override
  void addAllowedPointer(PointerDownEvent event) {
    // insert custom handling of event here...
    super.addAllowedPointer(event);
  }
}
```

## Timeline

Landed in version: 2.3.0-13.0.pre<br>
In stable release: 2.5

## References

API documentation:

* [`OneSequenceGestureRecognizer`][]

Relevant PR:

* [Fix addAllowedPointer() overrides][]

[`OneSequenceGestureRecognizer`]: https://api.flutter.dev/flutter/gestures/OneSequenceGestureRecognizer-class.html
[Fix addAllowedPointer() overrides]: https://github.com/flutter/flutter/pull/82834