docs: Fix non-web examples (#2411)

Fix build for non-web platforms, by hiding dart:html into platform-specific import.

examples/.gitignore

@@ -1,7 +1,6 @@
 linux/
 macos/
 windows/
-test/
 
 # Miscellaneous
 *.class

examples/lib/main.dart

@@ -1,5 +1,6 @@
-import 'dart:html';
 import 'package:dashbook/dashbook.dart';
+import 'package:examples/platform/stub_provider.dart'
+    if (dart.library.html) 'platform/web_provider.dart';
 import 'package:examples/stories/animations/animations.dart';
 import 'package:examples/stories/bridge_libraries/audio/audio.dart';
 import 'package:examples/stories/bridge_libraries/flame_isolate/isolate.dart';
@@ -29,10 +30,7 @@ import 'package:flame/game.dart';
 import 'package:flutter/material.dart';
 
 void main() {
-  var page = window.location.search ?? '';
-  if (page.startsWith('?')) {
-    page = page.substring(1);
-  }
+  final page = PageProviderImpl().getPage();
 
   final routes = <String, FlameGame Function()>{
     'constant_volume_joint': ConstantVolumeJointExample.new,

examples/lib/platform/page_provider.dart

@@ -0,0 +1,3 @@
+abstract class PageProvider {
+  String? getPage();
+}

examples/lib/platform/stub_provider.dart

@@ -0,0 +1,8 @@
+import 'package:examples/platform/page_provider.dart';
+
+class PageProviderImpl extends PageProvider {
+  @override
+  String? getPage() {
+    return null;
+  }
+}

examples/lib/platform/web_provider.dart

@@ -0,0 +1,13 @@
+import 'dart:html';
+import 'package:examples/platform/page_provider.dart';
+
+class PageProviderImpl extends PageProvider {
+  @override
+  String? getPage() {
+    var page = window.location.search ?? '';
+    if (page.startsWith('?')) {
+      page = page.substring(1);
+    }
+    return page;
+  }
+}

examples/pubspec.yaml

@@ -26,6 +26,7 @@ dependencies:
   padracing: ^1.0.0
   provider: ^6.0.3
   rogue_shooter: ^0.1.0
+  test: ^1.23.1
   trex_game: ^0.1.0
 
 dev_dependencies:

examples/test/main_test.dart

@@ -0,0 +1,6 @@
+import 'package:examples/main.dart' as examples;
+import 'package:test/test.dart';
+
+void main() {
+  test('main', examples.main);
+}