Navigator's page APIs breaking change

The Navigator page APIs are refactored so that they can integrate with Flutter's other pop mechanisms.

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.

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.

Code before migration:

dartimport '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:

dartimport '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);
        },
      ),
    ),
  );
}