How to Fix a Stretched Camera Preview in Flutter on Rotation

Are you experiencing a stretched or distorted camera preview in your Flutter app when the device rotates, even though you’re only supporting portrait mode? This is a common issue when using the camera package. This article provides a practical solution to lock the camera orientation and prevent unwanted stretching.

Understanding the Problem

The camera package, by default, attempts to adjust the camera preview based on the device’s orientation. In apps that are locked to a specific orientation (like portrait), this can lead to a mismatch between the app’s UI and the camera’s output, resulting in a stretched or broken preview.

Symptoms:

• Camera preview appears stretched horizontally or vertically when the device is rotated.
• The preview image might be cut off or distorted.
• This issue primarily occurs in apps that support only portrait or landscape mode and the camera tries to rotate.

The Solution: Locking the Capture Orientation

The key to fixing this is to explicitly lock the camera’s capture orientation to the desired orientation (e.g., DeviceOrientation.portraitUp) after initializing the CameraController.

Step-by-Step Guide

1. Initialize the Camera Controller: Create and initialize your CameraController as you normally would.
2. Lock the Capture Orientation: After the camera controller is initialized, call the lockCaptureOrientation() method, passing in the desired DeviceOrientation.

Code Example

 Future<void> initializeCamera() async {
  await controller?.dispose();
  controller = CameraController(
   _cameras.first, // or the camera you want to use.
   ResolutionPreset.max,
   enableAudio: false,
  );

  try {
   await controller!.initialize();
   //  Lock to portrait orientation **AFTER** initializing the controller
   await controller!.lockCaptureOrientation(DeviceOrientation.portraitUp);
  } catch (e) {
   print("Error initializing camera: $e");
   // Handle initialization errors here
  }

  // Notify listeners (if you're using a state management solution)
  notifyListeners();
 }
 

Explanation:

• The controller?.dispose() ensures that the previous controller is disposed of correctly before creating a new one, preventing memory leaks.
• The CameraController is initialized with the desired camera, resolution, and audio settings.
• The await controller!.initialize() call waits for the camera to be properly initialized.
• Crucially, the await controller!.lockCaptureOrientation(DeviceOrientation.portraitUp) line locks the camera’s output to portrait orientation.
• The try-catch block handles potential errors during camera initialization.

Common Errors and Solutions

Error: MissingPluginException(No implementation found for method lockCaptureOrientation on channel plugins.flutter.io/camera)

Cause: This usually indicates a problem with the camera plugin setup in your project.

Solution:

• Ensure the camera package is correctly added to your pubspec.yaml file. Double-check the package name and version.
• Run flutter pub get to fetch the dependencies.
• Clean and rebuild your project: flutter clean followed by flutter run
• Check platform-specific configurations: Ensure that the necessary permissions and configurations are set up correctly in your AndroidManifest.xml (for Android) and Info.plist (for iOS). Camera permissions are crucial.

Error: Camera preview is still stretched after implementing the fix.

Cause: Possible causes:

• The lockCaptureOrientation method is called before the camera is fully initialized.
• The UI is not correctly constrained to the screen’s bounds.

Solution:

• Ensure that you await the controller!.initialize() future *before* calling lockCaptureOrientation.
• Double-check the layout of your camera preview widget. Make sure it’s correctly constrained using widgets like AspectRatio, Expanded, or ConstrainedBox to prevent stretching.

Important Considerations

• Permissions: Remember to request necessary camera permissions from the user.
• State Management: Use a state management solution (Provider, Riverpod, Bloc, etc.) to handle the camera controller’s lifecycle and notify the UI of changes.
• Error Handling: Always include proper error handling when working with the camera to gracefully handle potential issues.

Conclusion

By locking the camera’s capture orientation, you can effectively prevent the stretched preview issue in Flutter apps that support a fixed orientation. This simple fix ensures a consistent and user-friendly camera experience. Remember to handle potential errors and manage camera permissions for a robust solution.

For more information on the camera package and its features, refer to the official documentation.