# Navigator's page APIs breaking change

> Replace Navigator's 'onPopPage' property with the 'onDidRemovePage' property.




:::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 [`Navigator`][] page APIs are refactored so that
they can integrate with Flutter's other pop mechanisms.

## Context

The `onPopPage` property was added for cleaning up pages after
a page is about to be popped.
To veto pop, you'd return `false` in the callback.
This did not work well with other popping mechanisms in the framework,
such as [`PopScope`][] and iOS back gestures.

To integrate the framework's pop mechanisms together,
the page APIs needed to be refactored.

## Description of change

The `onDidRemovePage` property replaces the `onPopPage` property.
You can no longer veto a pop in the `onDidRemovePage` property.
Instead, you are only responsible for updating the [`pages`][].

The veto mechanism is now managed with the
`Page.canPop` and `Page.onPopInvoked` properties.
These function similar to how you use the `PopScope` widget.

[`pages`]: https://api.flutter-io.cn/flutter/widgets/Navigator/pages.html

## Migration guide

Code before migration:

```dart
import 'package:flutter/material.dart';

final MaterialPage<void> page1 = MaterialPage<void>(child: Placeholder());
final MaterialPage<void> page2 = MaterialPage<void>(child: Placeholder());
final MaterialPage<void> page3 = MaterialPage<void>(child: Placeholder());

void main() {
  final List<Page<void>> pages = <Page<void>>[page1, page2, page3];
  runApp(
    MaterialApp(
      home: Navigator(
        pages: pages,
        onPopPage: (Route<Object?> route, Object? result) {
          if (route.settings == page2) {
            return false;
          }
          if (route.didPop) {
            pages.remove(route.settings);
            return true;
          }
          return false;
        },
      ),
    ),
  );
}
```

Code after migration:

```dart
import 'package:flutter/material.dart';

final MaterialPage<void> page1 = MaterialPage<void>(child: Placeholder());
final MaterialPage<void> page2 = MaterialPage<void>(canPop: false, child: Placeholder());
final MaterialPage<void> page3 = MaterialPage<void>(child: Placeholder());

void main() {
  final List<Page<void>> pages = <Page<void>>[page1, page2, page3];
  runApp(
    MaterialApp(
      home: Navigator(
        pages: pages,
        onDidRemovePage: (Page<Object?> page) {
          pages.remove(page);
        },
      ),
    ),
  );
}
```

## Timeline

Landed in version: 3.22.0-32.0.pre<br>
In stable release: 3.24.0

## References

API documentation:

* [`Navigator`][]
* [`PopScope`][]

Relevant issue:

* [Issue 137458][]

Relevant PR:

* [Refactors page API][]

[Refactors page API]: https://github.com/flutter/flutter/pull/137792
[`Navigator`]: https://api.flutter-io.cn/flutter/widgets/Navigator-class.html
[`PopScope`]: https://api.flutter-io.cn/flutter/widgets/PopScope-class.html
[Issue 137458]: https://github.com/flutter/flutter/issues/137458