Fix CameraView crash when switching camera on Windows and other CameraView enhancements

[zhitaop]

Description of Change

• Fixes [BUG] CameraView App crashes when switching camera on Windows #2559:

  Root cause :
  In CameraProvider.windows.cs, only one instance of MediaCapture is instantiated when iterating through the videoCaptureSourceGroup. This causes only the first mediaCapture.InitializeCameraForCameraView() to be successful. Wrong camera meta data from the first camera, such as the supported resolutions, are added to the subsequent CameraInfos (i.e. all subsequent CameraInfo contains metadata from the first CameraInfo). This causes the following exception when the camera is being updated with incorrect resolution:

  System.Runtime.InteropServices.COMException (0xC00D36B4): The data specified for the media type is invalid, inconsistent, or not supported by this object.
  The data specified for the media type is invalid, inconsistent, or not supported by this object.
  at CommunityToolkit.Maui.Core.CameraManager.PlatformUpdateResolution(Size resolution, CancellationToken token)

  Code changes:

  • Instantiate new MediaCapture in each iteration and properly dispose it after use

• Enhancement: refactor camera refresh logic

  Root cause:
  Multiple calls to CameraProvider.RefreshAvailableCameras() are scattered throughout the camera initialization code (i.e.in CameraManager.ConnectCamera, CameraManager.StartCameraPreview, CameraManager.UpdateResolution), which are unnecessary as the available cameras are unlikely to change during initialization, and also time consuming especially on Windows as it needs to initialize MediaCapture.

  In Addition, consumers of the camera view may also call RefreshAvailableCameras() (e.g. to populate the list for camera switcher), usually at the same time when the camera view itself is initializing , resulting in more redundant code execution.

  Code changes:

  • Add new properties and methods to CameraProvider:
    • internal: refreshTask and PlatformRefreshAvailableCameras()
    • public: InitializeAsync()
  • move camera refresh logic to PlatformRefreshAvailableCameras .
  • The refreshTask is reused for both initialization and refresh, ensuring only one refresh operation runs at a time.
  • InitializeAsync() only refreshes the cameras if the camera provide has not been initialized, i.e. the refreshTask is not completed successfully
  • RefreshAvailableCameras() only refreshes the cameras if the refresh task is not currently in progress, i.e. refreshTask is null or is completed (could be completed successfully, faulted or canceled)
  • Remove all RefreshAvailableCameras() calls in CameraManager and CameraViewHandler. Instead, call InitializeAsync() in CameraManager.ConnectCamera to ensure available cameras are initialized.

  Example usage by consumer:

// Initialization logic for camera view view model
public async Task InitializeAsync()
{
  await cameraProvider.InitializeAsync(CancellationToken.None); 
  Cameras = cameraProvider.AvailableCameras ?? [];
}

// Method to force camera to refresh. Can be used when cameras are changed, e.g. external usb camera is added
async Task RefreshCameras(CancellationToken token) => await cameraProvider.RefreshAvailableCameras(token);

• Enhancements in CameraViewPage and CameraViewViewModel:
  • Add camera switcher on the camera view page
  • Make Cameras observable in the view model, and make sure it's assigned after the CameraProvider is initialized so that camera list is not empty.

Linked Issues

• Fixes [BUG] CameraView App crashes when switching camera on Windows #2559

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

[VR-Architect]

Any guess when this will deploy to main? Hoping it fixes some issues I have with Windows camera.

[bijington]

Any guess when this will deploy to main? Hoping it fixes some issues I have with Windows camera.

Perhaps you could help us and test this branch on your machine to see if it helps?

[VR-Architect]

Any guess when this will deploy to main? Hoping it fixes some issues I have with Windows camera.

Perhaps you could help us and test this branch on your machine to see if it helps?

I would love to help but don't know how do download the branch to test. Let me Google it.

[ruc12127]

I have tested the CommunityToolkitSampleApp using https://github.com/zhitaop/CommunityToolkitMaui/tree/fix/camera-provider-refresh branch on Surface Book 3 (Windows 10). The camera switcher is working as expected without any crashes.

[zhitaop]

Hi @bijington, could this PR be assigned for review soon? As mentioned in #2634 (comment), the branch has been tested that it does solve the original crash issue.

[bijington]

Hi @bijington, could this PR be assigned for review soon? As mentioned in #2634 (comment), the branch has been tested that it does solve the original crash issue.

I've added some comments I didn't have a chance to take a look on a laptop so I'll try and do a more in depth check later in the week

[bijington]

Sorry it's taken time to get to this. I'll try and sort it tomorrow or next week

[vovanb]

I this it is same issue with recent code on Android

[zhitaop]

Hi @bijington, I've addressed some of your comments and provide explanation for others, could you please take a look again? Thanks!

[bijington]

Sorry things became really busy and then I went on vacation. I return at the weekend so I've added a reminder to take a look at this next week for you.

[bijington]

@zhitaop apologies for the delay in reviewing this. It looks good to me now!

[TheCodeTraveler]

Thanks @zhitaop! This is a breaking change that requires the docs to be updated before we can merge the PR: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

@bijington - could you work with @zhitaop on the updating the docs?

[Copilot]

Pull Request Overview

This PR fixes a critical CameraView crash on Windows when switching cameras and implements significant camera provider enhancements. The crash was caused by reusing a single MediaCapture instance across multiple cameras, leading to incorrect metadata assignment and resolution conflicts.

Key changes:

• Fixed Windows MediaCapture disposal and instantiation to prevent camera switching crashes
• Refactored camera initialization logic to reduce redundant refresh calls and improve performance
• Enhanced sample app with camera switcher UI and improved initialization patterns

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
CameraProvider.windows.cs	Fixed MediaCapture lifecycle management by creating new instances per camera and proper disposal
CameraProvider.shared.cs	Added thread-safe initialization logic with semaphore and task management
ICameraProvider.shared.cs	Extended interface with InitializeAsync method and IsInitialized property
CameraManager.*.cs	Removed redundant RefreshAvailableCameras calls and consolidated initialization logic
CameraViewHandler.shared.cs	Simplified connection logic by removing duplicate camera provider refresh
Sample app files	Enhanced UI with camera picker and improved initialization patterns

[Copilot]

Setting the task reference to null after disposing it creates a potential race condition. If another thread is checking refreshAvailableCamerasTask?.IsCompletedSuccessfully in the IsInitialized property while disposal is happening, it could access a disposed task. Consider setting the reference to null before disposing, or use a different synchronization approach.

Suggested change

	refreshAvailableCamerasTask?.Dispose();
	refreshAvailableCamerasTask = null;
	var task = refreshAvailableCamerasTask;
	refreshAvailableCamerasTask = null;
	task?.Dispose();

[zhitaop]

@TheCodeTraveler Thanks for the review and code update! I have raised a PR to update the documentation: MicrosoftDocs/CommunityToolkit#593

[zhitaop]

Hi @bijington @TheCodeTraveler, is there any update to the status of this PR?

[TheCodeTraveler]

Hi Zhitao! Yes we discussed it in our standup this month.

We've decided not to keep the breaking changes to the API in this PR and to only keep the bug fixes. The new Initialize method doesn't add much value for developers.

I will be closing this PR and reopening it with just the bug fix for Windows.

[zhitaop]

@TheCodeTraveler Thanks for the update!

Just to clarify, in my understanding, adding the InitializeAsync() method wouldn’t be a breaking change - it’s a new API that doesn’t affect any existing behaviour. Existing code using RefreshAvailableCameras() will continue to work as before without modification, developers do not have to use the new method.

The intent for adding the new method was to give developers more flexibility, as both methods serve different use cases:

• InitializeAsync only performs a one-time discovery of cameras and populates the AvailableCameras property. Subsequent calls will simply reuse the cached lists (a no-op).
• RefreshAvailableCameras forces a refresh. It always re-runs camera discovery to ensure the list is up to date

Camera discovery can be expensive, especially on Windows (it needs to initialize a mediaCapture object for each camera). In addition, camera availability on a device rarely changes during an app’s lifecycle, so InitializeAsync() provides the option to ensure the list is only initialized once.

For example, a view model for a camera view page can call InitializeAsync to populate a list of cameras when the page opens for the first time. Subsequent openings of the page do not need to refresh the cameras, increasing performance.

public async Task InitializeViewModelAsync()
{
  await cameraProvider.InitializeAsync(CancellationToken.None); 
// alternatively, call camepraProvider.RefreshAvailableCameras() to ensure the list is always up to date
  Cameras = cameraProvider.AvailableCameras ?? [];
} 

That said, if the concern is it adds unnecessary confusion to the API usage without adding too much value, I’m happy to update the PR and remove the InitializeAsync() method to keep it focused on the bug fix.

[TheCodeTraveler]

Thanks @zhitaop! No worries - I've opened the new PR here and would love your review! #2907