Refactor flutter command execution (#5892)

* refactor _run to runCmd

* replace requiresProjectRoot getter with call to commandValidator

* replace requiresDevice getter with call to findTargetDevice

* trace command requires a debug connection, not a device

* inline androidOnly getter

* rename command methods to verifyTheRunCmd and runCmd

* move common verification into BuildSubCommand

* rename deviceForCommand to device

* rename methods to verifyThenRunCommand and runCommand

packages/flutter_tools/lib/src/commands/analyze.dart

@@ -60,10 +60,7 @@ class AnalyzeCommand extends FlutterCommand {
   }
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() => argResults['watch'] ? _analyzeWatch() : _analyzeOnce();
+  Future<int> runCommand() => argResults['watch'] ? _analyzeWatch() : _analyzeOnce();
 
   List<String> flutterRootComponents;
   bool isFlutterLibrary(String filename) {

packages/flutter_tools/lib/src/commands/build.dart

@@ -32,13 +32,28 @@ class BuildCommand extends FlutterCommand {
   final String description = 'Flutter build commands.';
 
   @override
-  Future<int> runInProject() => new Future<int>.value(0);
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  Future<int> runCommand() => new Future<int>.value(0);
 }
 
 abstract class BuildSubCommand extends FlutterCommand {
   @override
   @mustCallSuper
-  Future<int> runInProject() async {
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  @mustCallSuper
+  Future<int> runCommand() async {
     if (isRunningOnBot) {
       File dotPackages = new File('.packages');
       printStatus('Contents of .packages:');
@@ -66,7 +81,14 @@ class BuildCleanCommand extends FlutterCommand {
   final String description = 'Delete the build/ directory.';
 
   @override
-  Future<int> runInProject() async {
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  Future<int> runCommand() async {
     Directory buildDir = new Directory(getBuildDirectory());
     printStatus("Deleting '${buildDir.path}${Platform.pathSeparator}'.");
 

packages/flutter_tools/lib/src/commands/build_aot.dart

@@ -42,8 +42,8 @@ class BuildAotCommand extends BuildSubCommand {
   final String description = "Build an ahead-of-time compiled snapshot of your app's Dart code.";
 
   @override
-  Future<int> runInProject() async {
-    await super.runInProject();
+  Future<int> runCommand() async {
+    await super.runCommand();
     String targetPlatform = argResults['target-platform'];
     TargetPlatform platform = getTargetPlatformForName(targetPlatform);
     if (platform == null) {

packages/flutter_tools/lib/src/commands/build_apk.dart

@@ -221,8 +221,8 @@ class BuildApkCommand extends BuildSubCommand {
   }
 
   @override
-  Future<int> runInProject() async {
-    await super.runInProject();
+  Future<int> runCommand() async {
+    await super.runCommand();
 
     TargetPlatform targetPlatform = _getTargetPlatform(argResults['target-arch']);
     if (targetPlatform != TargetPlatform.android_arm && getBuildMode() != BuildMode.debug) {

packages/flutter_tools/lib/src/commands/build_flx.dart

@@ -38,8 +38,8 @@ class BuildFlxCommand extends BuildSubCommand {
     'they are used by some Flutter Android and iOS runtimes.';
 
   @override
-  Future<int> runInProject() async {
-    await super.runInProject();
+  Future<int> runCommand() async {
+    await super.runCommand();
     String outputPath = argResults['output-file'];
 
     return await build(

packages/flutter_tools/lib/src/commands/build_ios.dart

@@ -38,11 +38,11 @@ class BuildIOSCommand extends BuildSubCommand {
   final String description = 'Build an iOS application bundle (Mac OS X host only).';
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     bool forSimulator = argResults['simulator'];
     defaultBuildMode = forSimulator ? BuildMode.debug : BuildMode.release;
 
-    await super.runInProject();
+    await super.runCommand();
     if (getCurrentHostPlatform() != HostPlatform.darwin_x64) {
       printError('Building for iOS is only supported on the Mac.');
       return 1;

packages/flutter_tools/lib/src/commands/channel.dart

@@ -20,10 +20,7 @@ class ChannelCommand extends FlutterCommand {
   String get invocation => '${runner.executableName} $name [<channel-name>]';
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     switch (argResults.rest.length) {
       case 0:
         return await _listChannels();

packages/flutter_tools/lib/src/commands/config.dart

@@ -41,15 +41,12 @@ class ConfigCommand extends FlutterCommand {
       'Analytics reporting is currently ${flutterUsage.enabled ? 'enabled' : 'disabled'}.';
   }
 
-  @override
-  bool get requiresProjectRoot => false;
-
   /// Return `null` to disable tracking of the `config` command.
   @override
   String get usagePath => null;
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if (argResults.wasParsed('analytics')) {
       bool value = argResults['analytics'];
       flutterUsage.enabled = value;

packages/flutter_tools/lib/src/commands/create.dart

@@ -41,14 +41,11 @@ class CreateCommand extends FlutterCommand {
   final String description = 'Create a new Flutter project.\n\n'
     'If run on a project that already exists, this will repair the project, recreating any files that are missing.';
 
-  @override
-  bool get requiresProjectRoot => false;
-
   @override
   String get invocation => "${runner.executableName} $name <output directory>";
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if (argResults.rest.isEmpty) {
       printStatus('No option specified for the output directory.');
       printStatus(usage);

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -37,14 +37,11 @@ class DaemonCommand extends FlutterCommand {
   @override
   final String description = 'Run a persistent, JSON-RPC based server to communicate with devices.';
 
-  @override
-  bool get requiresProjectRoot => false;
-
   @override
   final bool hidden;
 
   @override
-  Future<int> runInProject() {
+  Future<int> runCommand() {
     printStatus('Starting device daemon...');
 
     AppContext appContext = new AppContext();

packages/flutter_tools/lib/src/commands/devices.dart

@@ -17,10 +17,7 @@ class DevicesCommand extends FlutterCommand {
   final String description = 'List all connected devices.';
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if (!doctor.canListAnything) {
       printError("Unable to locate a development device; please run 'flutter doctor' for "
         "information about installing additional components.");

packages/flutter_tools/lib/src/commands/doctor.dart

@@ -15,10 +15,7 @@ class DoctorCommand extends FlutterCommand {
   final String description = 'Show information about the installed tooling.';
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     await doctor.diagnose();
     return 0;
   }

packages/flutter_tools/lib/src/commands/drive.dart

@@ -86,7 +86,14 @@ class DriveCommand extends RunCommandBase {
   int get debugPort => int.parse(argResults['debug-port']);
 
   @override
-  Future<int> runInProject() async {
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  Future<int> runCommand() async {
     String testFile = _getTestFile();
     if (testFile == null) {
       return 1;

packages/flutter_tools/lib/src/commands/format.dart

@@ -21,14 +21,11 @@ class FormatCommand extends FlutterCommand {
   @override
   final String description = 'Format one or more dart files.';
 
-  @override
-  bool get requiresProjectRoot => false;
-
   @override
   String get invocation => "${runner.executableName} $name <one or more paths>";
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if (argResults.rest.isEmpty) {
       printStatus('No files specified to be formatted.');
       printStatus('');

packages/flutter_tools/lib/src/commands/install.dart

@@ -17,12 +17,20 @@ class InstallCommand extends FlutterCommand {
   @override
   final String description = 'Install a Flutter app on an attached device.';
 
+  Device device;
+
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    device = await findTargetDevice();
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
-    Device device = deviceForCommand;
+  Future<int> runCommand() async {
     ApplicationPackage package = applicationPackages.getPackageForPlatform(device.platform);
 
     Cache.releaseLockEarly();

packages/flutter_tools/lib/src/commands/listen.dart

@@ -29,11 +29,20 @@ class ListenCommand extends RunCommandBase {
   /// Only run once. Used for testing.
   final bool singleRun;
 
+  Device device;
+
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    device = await findTargetDevice();
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     Iterable<String> directories = () sync* {
       yield* argResults.rest;
       yield '.';
@@ -61,7 +70,7 @@ class ListenCommand extends RunCommandBase {
         printStatus('Re-running app...');
 
       result = await startApp(
-        deviceForCommand,
+        device,
         target: targetFile,
         install: firstTime,
         stop: true,

packages/flutter_tools/lib/src/commands/logs.dart

@@ -25,16 +25,18 @@ class LogsCommand extends FlutterCommand {
   @override
   final String description = 'Show log output for running Flutter apps.';
 
-  @override
-  bool get requiresProjectRoot => false;
+  Device device;
 
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    device = await findTargetDevice();
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
-    Device device = deviceForCommand;
-
+  Future<int> runCommand() async {
     if (argResults['clear'])
       device.clearLogs();
 

packages/flutter_tools/lib/src/commands/packages.dart

@@ -25,7 +25,14 @@ class PackagesCommand extends FlutterCommand {
   final String description = 'Commands for managing Flutter packages.';
 
   @override
-  Future<int> runInProject() => new Future<int>.value(0);
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  Future<int> runCommand() => new Future<int>.value(0);
 }
 
 class PackagesGetCommand extends FlutterCommand {
@@ -41,15 +48,12 @@ class PackagesGetCommand extends FlutterCommand {
   String get description =>
       (upgrade ? 'Upgrade' : 'Get') + ' packages in a Flutter project.';
 
-  @override
-  bool get requiresProjectRoot => false;
-
   @override
   String get invocation =>
       "${runner.executableName} packages $name [<target directory>]";
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if (argResults.rest.length > 1) {
       printStatus('Too many arguments.');
       printStatus(usage);

packages/flutter_tools/lib/src/commands/precache.dart

@@ -20,10 +20,7 @@ class PrecacheCommand extends FlutterCommand {
   final String description = 'Populates the Flutter tool\'s cache of binary artifacts.';
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if (argResults['all-platforms'])
       cache.includeAllPlatforms = true;
 

packages/flutter_tools/lib/src/commands/refresh.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:flutter_tools/src/device.dart';
 import 'package:path/path.dart' as path;
 
 import '../android/android_device.dart';
@@ -29,14 +30,20 @@ class RefreshCommand extends FlutterCommand {
     );
   }
 
-  @override
-  bool get androidOnly => true;
+  Device device;
 
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    device = await findTargetDevice(androidOnly: true);
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     Directory tempDir = await Directory.systemTemp.createTemp('flutter_tools');
     try {
       String snapshotPath = path.join(tempDir.path, 'snapshot_blob.bin');
@@ -49,8 +56,6 @@ class RefreshCommand extends FlutterCommand {
 
       Cache.releaseLockEarly();
 
-      AndroidDevice device = deviceForCommand;
-
       String activity = argResults['activity'];
       if (activity == null) {
         AndroidApk apk = applicationPackages.getPackageForPlatform(device.platform);
@@ -62,7 +67,9 @@ class RefreshCommand extends FlutterCommand {
         }
       }
 
-      bool success = await device.refreshSnapshot(activity, snapshotPath);
+      AndroidDevice androidDevice = device;
+
+      bool success = await androidDevice.refreshSnapshot(activity, snapshotPath);
       if (!success) {
         printError('Error refreshing snapshot on $device.');
         return 1;

packages/flutter_tools/lib/src/commands/run.dart

@@ -83,13 +83,10 @@ class RunCommand extends RunCommandBase {
     argParser.addFlag('benchmark', negatable: false, hide: true);
   }
 
-  @override
-  bool get requiresDevice => true;
+  Device device;
 
   @override
   String get usagePath {
-    Device device = deviceForCommand;
-
     String command = shouldUseHotMode() ? 'hotrun' : name;
 
     if (device == null)
@@ -116,7 +113,17 @@ class RunCommand extends RunCommandBase {
   }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    device = await findTargetDevice();
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  Future<int> runCommand() async {
     int debugPort;
 
     if (argResults['debug-port'] != null) {
@@ -128,7 +135,7 @@ class RunCommand extends RunCommandBase {
       }
     }
 
-    if (deviceForCommand.isLocalEmulator && !isEmulatorBuildMode(getBuildMode())) {
+    if (device.isLocalEmulator && !isEmulatorBuildMode(getBuildMode())) {
       printError('${toTitleCase(getModeName(getBuildMode()))} mode is not supported for emulators.');
       return 1;
     }
@@ -152,7 +159,7 @@ class RunCommand extends RunCommandBase {
     final bool hotMode = shouldUseHotMode();
 
     if (hotMode) {
-      if (!deviceForCommand.supportsHotMode) {
+      if (!device.supportsHotMode) {
         printError('Hot mode is not supported by this device. '
                    'Run with --no-hot.');
         return 1;
@@ -168,14 +175,14 @@ class RunCommand extends RunCommandBase {
 
     if (hotMode) {
       runner = new HotRunner(
-        deviceForCommand,
+        device,
         target: targetFile,
         debuggingOptions: options,
         benchmarkMode: argResults['benchmark'],
       );
     } else {
       runner = new RunAndStayResident(
-        deviceForCommand,
+        device,
         target: targetFile,
         debuggingOptions: options,
         traceStartup: traceStartup,

packages/flutter_tools/lib/src/commands/run_mojo.dart

@@ -42,9 +42,6 @@ class RunMojoCommand extends FlutterCommand {
   @override
   final bool hidden;
 
-  @override
-  bool get requiresProjectRoot => false;
-
   // TODO(abarth): Why not use path.absolute?
   String _makePathAbsolute(String relativePath) {
     File file = new File(relativePath);
@@ -127,7 +124,7 @@ class RunMojoCommand extends FlutterCommand {
   }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     if ((argResults['mojo-path'] == null && argResults['devtools-path'] == null) || (argResults['mojo-path'] != null && argResults['devtools-path'] != null)) {
       printError('Must specify either --mojo-path or --devtools-path.');
       return 1;

packages/flutter_tools/lib/src/commands/screenshot.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:flutter_tools/src/device.dart';
 import 'package:path/path.dart' as path;
 
 import '../base/utils.dart';
@@ -27,16 +28,20 @@ class ScreenshotCommand extends FlutterCommand {
   @override
   final List<String> aliases = <String>['pic'];
 
-  @override
-  bool get requiresProjectRoot => false;
+  Device device;
 
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    device = await findTargetDevice();
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
-    if (!deviceForCommand.supportsScreenshot) {
-      printError('Screenshot not supported for ${deviceForCommand.name}.');
+  Future<int> runCommand() async {
+    if (!device.supportsScreenshot) {
+      printError('Screenshot not supported for ${device.name}.');
       return 1;
     }
 
@@ -49,7 +54,7 @@ class ScreenshotCommand extends FlutterCommand {
     }
 
     try {
-      bool result = await deviceForCommand.takeScreenshot(outputFile);
+      bool result = await device.takeScreenshot(outputFile);
 
       if (result) {
         int sizeKB = outputFile.lengthSync() ~/ 1000;

packages/flutter_tools/lib/src/commands/setup.dart

@@ -31,10 +31,7 @@ class SetupCommand extends FlutterCommand {
   final bool hidden;
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     printStatus('Running Flutter setup...');
 
     // setup brew on mac

packages/flutter_tools/lib/src/commands/skia.dart

@@ -27,7 +27,14 @@ class SkiaCommand extends FlutterCommand {
   final String description = 'Retrieve the last frame rendered by a Flutter app as a Skia picture.';
 
   @override
-  Future<int> runInProject() async {
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
+
+  @override
+  Future<int> runCommand() async {
     File outputFile;
     Uri skiaserveUri;
     if (argResults['output-file'] != null) {

packages/flutter_tools/lib/src/commands/stop.dart

@@ -17,12 +17,20 @@ class StopCommand extends FlutterCommand {
   @override
   final String description = 'Stop your Flutter app on an attached device.';
 
+  Device device;
+
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    device = await findTargetDevice();
+    if (device == null)
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
-    Device device = deviceForCommand;
+  Future<int> runCommand() async {
     ApplicationPackage app = applicationPackages.getPackageForPlatform(device.platform);
     if (app == null) {
       String platformName = getNameForTargetPlatform(device.platform);

packages/flutter_tools/lib/src/commands/test.dart

@@ -44,9 +44,6 @@ class TestCommand extends FlutterCommand {
   @override
   String get description => 'Run Flutter unit tests for the current project.';
 
-  @override
-  bool get requiresProjectRoot => false;
-
   @override
   Validator commandValidator = () {
     if (!FileSystemEntity.isFileSync('pubspec.yaml')) {
@@ -147,7 +144,7 @@ class TestCommand extends FlutterCommand {
   }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     List<String> testArgs = argResults.rest.map((String testPath) => path.absolute(testPath)).toList();
 
     if (!commandValidator())

packages/flutter_tools/lib/src/commands/trace.dart

@@ -46,10 +46,14 @@ class TraceCommand extends FlutterCommand {
     'with --start and later with --stop.';
 
   @override
-  bool get requiresDevice => true;
+  Future<int> verifyThenRunCommand() async {
+    if (!commandValidator())
+      return 1;
+    return super.verifyThenRunCommand();
+  }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     int observatoryPort = int.parse(argResults['debug-port']);
 
     Tracing tracing;

packages/flutter_tools/lib/src/commands/update_packages.dart

@@ -32,9 +32,6 @@ class UpdatePackagesCommand extends FlutterCommand {
   @override
   final bool hidden;
 
-  @override
-  bool get requiresProjectRoot => false;
-
   Future<Null> _downloadCoverageData() async {
     Status status = logger.startProgress("Downloading lcov data for package:flutter...");
     final List<int> data = await fetchUrl(Uri.parse('https://storage.googleapis.com/flutter_infra/flutter/coverage/lcov.info'));
@@ -49,7 +46,7 @@ class UpdatePackagesCommand extends FlutterCommand {
   }
 
   @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     try {
       final Stopwatch timer = new Stopwatch()..start();
       int count = 0;

packages/flutter_tools/lib/src/commands/upgrade.dart

@@ -21,10 +21,7 @@ class UpgradeCommand extends FlutterCommand {
   final String description = 'Upgrade your copy of Flutter.';
 
   @override
-  bool get requiresProjectRoot => false;
-
-  @override
-  Future<int> runInProject() async {
+  Future<int> runCommand() async {
     try {
       runCheckedSync(<String>[
         'git', 'rev-parse', '@{u}'

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:io';
 
 import 'package:args/command_runner.dart';
+import 'package:meta/meta.dart';
 
 import '../application_package.dart';
 import '../build_info.dart';
@@ -27,15 +28,6 @@ abstract class FlutterCommand extends Command {
   @override
   FlutterCommandRunner get runner => super.runner;
 
-  /// Whether this command needs to be run from the root of a project.
-  bool get requiresProjectRoot => true;
-
-  /// Whether this command requires a (single) Flutter target device to be connected.
-  bool get requiresDevice => false;
-
-  /// Whether this command only applies to Android devices.
-  bool get androidOnly => false;
-
   /// Whether this command uses the 'target' option.
   bool _usesTargetOption = false;
 
@@ -100,7 +92,7 @@ abstract class FlutterCommand extends Command {
     return _defaultBuildMode;
   }
 
-  void _setupApplicationPackages() {
+  void setupApplicationPackages() {
     applicationPackages ??= new ApplicationPackageStore();
   }
 
@@ -108,12 +100,21 @@ abstract class FlutterCommand extends Command {
   /// tracking of the command.
   String get usagePath => name;
 
+  /// Runs this command.
+  ///
+  /// Rather than overriding this method, subclasses should override
+  /// [verifyThenRunCommand] to perform any verification
+  /// and [runCommand] to execute the command
+  /// so that this method can record and report the overall time to analytics.
   @override
   Future<int> run() {
     Stopwatch stopwatch = new Stopwatch()..start();
     UsageTimer analyticsTimer = usagePath == null ? null : flutterUsage.startTimer(name);
 
-    return _run().then((int exitCode) {
+    if (flutterUsage.isFirstRun)
+      flutterUsage.printUsage();
+
+    return verifyThenRunCommand().then((int exitCode) {
       int ms = stopwatch.elapsedMilliseconds;
       printTrace("'flutter $name' took ${ms}ms; exiting with code $exitCode.");
       analyticsTimer?.finish();
@@ -121,55 +122,15 @@ abstract class FlutterCommand extends Command {
     });
   }
 
-  Future<int> _run() async {
-    if (requiresProjectRoot && !commandValidator())
-      return 1;
-
-    // Ensure at least one toolchain is installed.
-    if (requiresDevice && !doctor.canLaunchAnything) {
-      printError("Unable to locate a development device; please run 'flutter doctor' "
-        "for information about installing additional components.");
-      return 1;
-    }
-
-    // Validate devices.
-    if (requiresDevice) {
-      List<Device> devices = await deviceManager.getDevices();
-
-      if (devices.isEmpty && deviceManager.hasSpecifiedDeviceId) {
-        printStatus("No devices found with name or id "
-            "matching '${deviceManager.specifiedDeviceId}'");
-        return 1;
-      } else if (devices.isEmpty) {
-        printNoConnectedDevices();
-        return 1;
-      }
-
-      devices = devices.where((Device device) => device.isSupported()).toList();
-
-      if (androidOnly)
-        devices = devices.where((Device device) => device.platform == TargetPlatform.android_arm).toList();
-
-      if (devices.isEmpty) {
-        printStatus('No supported devices connected.');
-        return 1;
-      } else if (devices.length > 1) {
-        if (deviceManager.hasSpecifiedDeviceId) {
-          printStatus("Found ${devices.length} devices with name or id matching "
-              "'${deviceManager.specifiedDeviceId}':");
-        } else {
-          printStatus("More than one device connected; please specify a device with "
-              "the '-d <deviceId>' flag.");
-          devices = await deviceManager.getAllConnectedDevices();
-        }
-        printStatus('');
-        Device.printDevices(devices);
-        return 1;
-      } else {
-        _deviceForCommand = devices.single;
-      }
-    }
-
+  /// Perform validation then call [runCommand] to execute the command.
+  /// Return a [Future] that completes with an exit code
+  /// indicating whether execution was successful.
+  ///
+  /// Subclasses should override this method to perform verification
+  /// then call this method to execute the command
+  /// rather than calling [runCommand] directly.
+  @mustCallSuper
+  Future<int> verifyThenRunCommand() async {
     // Populate the cache. We call this before pub get below so that the sky_engine
     // package is available in the flutter cache for pub to find.
     await cache.updateAll();
@@ -180,16 +141,62 @@ abstract class FlutterCommand extends Command {
         return exitCode;
     }
 
-    if (flutterUsage.isFirstRun)
-      flutterUsage.printUsage();
-
-    _setupApplicationPackages();
+    setupApplicationPackages();
 
     String commandPath = usagePath;
     if (commandPath != null)
       flutterUsage.sendCommand(usagePath);
 
-    return await runInProject();
+    return await runCommand();
+  }
+
+  /// Subclasses must implement this to execute the command.
+  Future<int> runCommand();
+
+  /// Find and return the target [Device] based upon currently connected
+  /// devices and criteria entered by the user on the command line.
+  /// If a device cannot be found that meets specified criteria,
+  /// then print an error message and return `null`.
+  Future<Device> findTargetDevice({bool androidOnly: false}) async {
+    if (!doctor.canLaunchAnything) {
+      printError("Unable to locate a development device; please run 'flutter doctor' "
+          "for information about installing additional components.");
+      return null;
+    }
+
+    List<Device> devices = await deviceManager.getDevices();
+
+    if (devices.isEmpty && deviceManager.hasSpecifiedDeviceId) {
+      printStatus("No devices found with name or id "
+          "matching '${deviceManager.specifiedDeviceId}'");
+      return null;
+    } else if (devices.isEmpty) {
+      printNoConnectedDevices();
+      return null;
+    }
+
+    devices = devices.where((Device device) => device.isSupported()).toList();
+
+    if (androidOnly)
+      devices = devices.where((Device device) => device.platform == TargetPlatform.android_arm).toList();
+
+    if (devices.isEmpty) {
+      printStatus('No supported devices connected.');
+      return null;
+    } else if (devices.length > 1) {
+      if (deviceManager.hasSpecifiedDeviceId) {
+        printStatus("Found ${devices.length} devices with name or id matching "
+            "'${deviceManager.specifiedDeviceId}':");
+      } else {
+        printStatus("More than one device connected; please specify a device with "
+            "the '-d <deviceId>' flag.");
+        devices = await deviceManager.getAllConnectedDevices();
+      }
+      printStatus('');
+      Device.printDevices(devices);
+      return null;
+    }
+    return devices.single;
   }
 
   void printNoConnectedDevices() {
@@ -230,12 +237,5 @@ abstract class FlutterCommand extends Command {
     return true;
   }
 
-  Future<int> runInProject();
-
-  // This is calculated in run() if the command has [requiresDevice] specified.
-  Device _deviceForCommand;
-
-  Device get deviceForCommand => _deviceForCommand;
-
   ApplicationPackageStore applicationPackages;
 }