Migrate external_ui to null safety (#80640)

dev/integration_tests/external_ui/lib/main.dart

@@ -15,7 +15,7 @@ void main() {
 }
 
 class MyApp extends StatefulWidget {
-  const MyApp({Key key}) : super(key: key);
+  const MyApp({Key? key}) : super(key: key);
 
   @override
   State createState() => MyAppState();
@@ -27,17 +27,17 @@ enum FrameState { initial, slow, afterSlow, fast, afterFast }
 
 class MyAppState extends State<MyApp> with SingleTickerProviderStateMixin {
   int _widgetBuilds = 0;
-  FrameState _state;
+  FrameState _state = FrameState.initial;
   String _summary = '';
-  IconData _icon;
-  double _flutterFrameRate;
+  IconData? _icon;
+  double _flutterFrameRate = 0;
 
   Future<void> _summarizeStats() async {
-    final double framesProduced = await channel.invokeMethod('getProducedFrameRate');
-    final double framesConsumed = await channel.invokeMethod('getConsumedFrameRate');
+    final double? framesProduced = await channel.invokeMethod('getProducedFrameRate');
+    final double? framesConsumed = await channel.invokeMethod('getConsumedFrameRate');
     _summary = '''
-Produced: ${framesProduced.toStringAsFixed(1)}fps
-Consumed: ${framesConsumed.toStringAsFixed(1)}fps
+Produced: ${framesProduced?.toStringAsFixed(1)}fps
+Consumed: ${framesConsumed?.toStringAsFixed(1)}fps
 Widget builds: $_widgetBuilds''';
   }
 
@@ -96,15 +96,15 @@ Widget builds: $_widgetBuilds''';
     debugPrint('Awaiting calm (3 second pause)...');
     await Future<void>.delayed(const Duration(milliseconds: 3000));
     debugPrint('Calibrating...');
-    DateTime startTime;
+    late DateTime startTime;
     int tickCount = 0;
-    Ticker ticker;
+    Ticker? ticker;
     ticker = createTicker((Duration time) {
       tickCount += 1;
       if (tickCount == calibrationTickCount) { // about 10 seconds
         final Duration elapsed = DateTime.now().difference(startTime);
-        ticker.stop();
-        ticker.dispose();
+        ticker?.stop();
+        ticker?.dispose();
         setState(() {
           _flutterFrameRate = tickCount * 1000 / elapsed.inMilliseconds;
           debugPrint('Calibrated: frame rate ${_flutterFrameRate.toStringAsFixed(1)}fps.');

dev/integration_tests/external_ui/pubspec.yaml

@@ -2,7 +2,7 @@ name: external_ui
 description: A test of Flutter integrating external UIs.
 
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:

dev/integration_tests/external_ui/test_driver/main_test.dart

@@ -13,7 +13,7 @@ const Duration samplingTime = Duration(seconds: 8);
 
 Future<void> main() async {
   group('texture suite', () {
-    FlutterDriver driver;
+    late FlutterDriver driver;
 
     setUpAll(() async {
       driver = await FlutterDriver.connect();
@@ -32,9 +32,9 @@ Future<void> main() async {
       await driver.waitFor(fab);
 
       final String calibrationResult = await driver.getText(summary);
-      final Match matchCalibration = calibrationRegExp.matchAsPrefix(calibrationResult);
+      final Match? matchCalibration = calibrationRegExp.matchAsPrefix(calibrationResult);
       expect(matchCalibration, isNotNull);
-      final double flutterFrameRate = double.parse(matchCalibration.group(1));
+      final double flutterFrameRate = double.parse(matchCalibration?.group(1) ?? '0');
 
       // Texture frame stats at 0.5x Flutter frame rate
       await driver.tap(fab);
@@ -42,11 +42,11 @@ Future<void> main() async {
       await driver.tap(fab);
 
       final String statsSlow = await driver.getText(summary);
-      final Match matchSlow = statsRegExp.matchAsPrefix(statsSlow);
+      final Match matchSlow = statsRegExp.matchAsPrefix(statsSlow)!;
       expect(matchSlow, isNotNull);
-      expect(double.parse(matchSlow.group(1)), closeTo(flutterFrameRate / 2.0, 5.0));
-      expect(double.parse(matchSlow.group(2)), closeTo(flutterFrameRate / 2.0, 5.0));
-      expect(int.parse(matchSlow.group(3)), 1);
+      expect(double.parse(matchSlow.group(1)!), closeTo(flutterFrameRate / 2.0, 5.0));
+      expect(double.parse(matchSlow.group(2)!), closeTo(flutterFrameRate / 2.0, 5.0));
+      expect(int.parse(matchSlow.group(3)!), 1);
 
       // Texture frame stats at 2.0x Flutter frame rate
       await driver.tap(fab);
@@ -54,15 +54,15 @@ Future<void> main() async {
       await driver.tap(fab);
 
       final String statsFast = await driver.getText(summary);
-      final Match matchFast = statsRegExp.matchAsPrefix(statsFast);
+      final Match matchFast = statsRegExp.matchAsPrefix(statsFast)!;
       expect(matchFast, isNotNull);
-      expect(double.parse(matchFast.group(1)), closeTo(flutterFrameRate * 2.0, 5.0));
-      expect(double.parse(matchFast.group(2)), closeTo(flutterFrameRate, 10.0));
-      expect(int.parse(matchFast.group(3)), 1);
+      expect(double.parse(matchFast.group(1)!), closeTo(flutterFrameRate * 2.0, 5.0));
+      expect(double.parse(matchFast.group(2)!), closeTo(flutterFrameRate, 10.0));
+      expect(int.parse(matchFast.group(3)!), 1);
     });
 
     tearDownAll(() async {
-      driver?.close();
+      driver.close();
     });
   });
 }