Debug your add-to-app module

Once you’ve integrated the Flutter module to your project and used Flutter’s platform APIs to run the Flutter engine and/or UI, you can then build and run your Android or iOS app the same way you run normal Android or iOS apps.

However, Flutter is now powering the UI in places where you’re showing a FlutterActivity or FlutterViewController.

Debugging

You might be used to having your suite of favorite Flutter debugging tools available to you automatically when running flutter run or an equivalent command from an IDE. But you can also use all your Flutter debugging functionalities such as hot reload, performance overlays, DevTools, and setting breakpoints in add-to-app scenarios.

These functionalities are provided by the flutter attach mechanism. flutter attach can be initiated through different pathways, such as through the SDK’s CLI tools, through VS Code or IntelliJ/Android Studio.

flutter attach can connect as soon as you run your FlutterEngine, and remains attached until your FlutterEngine is disposed. But you can invoke flutter attach before starting your engine. flutter attach waits for the next available Dart VM that is hosted by your engine.

Terminal

Run flutter attach or flutter attach -d deviceId to attach from the terminal.

flutter attach via terminal
flutter attach via terminal

VS Code

Build the iOS version of the Flutter app in the Terminal

To generate the needed iOS platform dependencies, run the flutter build command.

flutter build ios --config-only --no-codesign --debug
Warning: Building for device with codesigning disabled. You will have to manually codesign before deploying to device.
Building com.example.myApp for device (ios)...

Start debugging with VS Code first

If you use VS Code to debug most of your code, start with this section.

Start the Dart debugger in VS Code
  1. To open the Flutter app directory, go to File > Open Folder… and choose the my_app directory.

  2. Open the lib/main.dart file.

  3. If you can build an app for more than one device, you must select the device first.

    Go to View > Command Palette…

    You can also press Ctrl / Cmd + Shift + P.

  4. Type flutter select.

  5. Click the Flutter: Select Device command.

  6. Choose your target device.

  7. Click the debug icon (VS Code's bug icon to trigger the debugging mode of a Flutter app). This opens the Debug pane and launches the app. Wait for the app to launch on the device and for the debug pane to indicate Connected. The debugger takes longer to launch the first time. Subsequent launches start faster.

    This Flutter app contains two buttons:

    • Launch in browser: This button opens this page in the default browser of your device.
    • Launch in app: This button opens this page within your app. This button only works for iOS or Android. Desktop apps launch a browser.
Attach to the Flutter process in Xcode
  1. To attach to the Flutter app, go to Debug > Attach to Process > Runner.

    Runner should be at the top of the Attach to Process menu under the Likely Targets heading.

Start debugging with Xcode first

If you use Xcode to debug most of your code, start with this section.

Start the Xcode debugger
  1. Open ios/Runner.xcworkspace from your Flutter app directory.

  2. Select the correct device using the Scheme menu in the toolbar.

    If you have no preference, choose iPhone Pro 14.

  3. Run this Runner as a normal app in Xcode.

    When the run completes, the Debug area at the bottom of Xcode displays a message with the Dart VM service URI. It resembles the following response:

     2023-07-12 14:55:39.966191-0500 Runner[58361:53017145]
         flutter: The Dart VM service is listening on
         http://127.0.0.1:50642/00wEOvfyff8=/
    
  4. Copy the Dart VM service URI.

Attach to the Dart VM in VS Code
  1. To open the command palette, go to View > Command Palette…

    You can also press Cmd + Shift + P.

  2. Type debug.

  3. Click the Debug: Attach to Flutter on Device command.

  4. In the Paste an VM Service URI box, paste the URI you copied from Xcode and press Enter.

You can also create a .vscode/launch.json file in your Flutter module project. This enables you to attach using the Run > Start Debugging command or F5:

{
  name: "Flutter: Attach",
  request: "attach",
  type: "dart",
}

IntelliJ / Android Studio

Select the device on which the Flutter module runs so flutter attach filters for the right start signals.

flutter attach via IntelliJ
flutter attach via IntelliJ

Wireless debugging

You can debug your app wirelessly on an iOS or Android device using flutter attach.

iOS

On iOS, you must follow the steps below:

  1. Ensure that your device is wirelessly connected to Xcode as described in the iOS setup guide.

  2. Open Xcode > Product > Scheme > Edit Scheme

  3. Select the Arguments tab

  4. Add either --vm-service-host=0.0.0.0 for IPv4, or --vm-service-host=::0 for IPv6 as a launch argument

    You can determine if you’re on an IPv6 network by opening your Mac’s Settings > Wi-Fi > Details (of the network you’re connected to) > TCP/IP and check to see if there is an IPv6 address section.

    Check the box that says 'connect via network' from the devices and simulators page

Android

Ensure that your device is wirelessly connected to Android Studio as described in the Android setup guide.