[Bug] UI Freeze and 'Cannot Access a Disposed Object' Error While Continuously Scanning Barcodes or Repeatedly Scanning a Single Barcode

[HaileyKim04]

Description

This issue arises when scanning a single barcode for an extended period, when the camera stops functioning after multiple scans, or when switching between barcode scanning and unrelated screens (e.g., a barcode image or any random background)**

Steps to Reproduce

1. Navigate to a page containing CameraView.
2. Scan a barcode.
3. Switch back and forth between barcode scanning and unrelated screens multiple times.
4. The issue manifests as the camera freezing or stopping after several repeated cycles.

Expected Behavior

• The camera should continue functioning without freezing or stopping, regardless of the duration of scanning or repeated interactions with unrelated pages/screens.

Actual Behavior

• The camera stops working or freezes.
• Error thrown: Cannot access a disposed object. Object name: 'AndroidX.Camera.View.Transform.CoordinateTransform'.

Basic Information

• Version with issue: 1.4.19
• Last known good version:

Screenshots, Attachments, Links

Cannot access a disposed object. Object name: 'AndroidX.Camera.View.Transform.CoordinateTransform'.

[HaileyKim04]

Hello @thomasgalliker , In the context of BarcodeAnalyze under Android codebase, the current implementation catches exceptions and log it

catch (Exception ex)
{
    this.logger.LogError(ex, "Analyze failed with exception");
}

I’m wondering if this supposed to be throwing the exception

[thomasgalliker]

Thanks for reporting this issue. I have to look at it.
Regarding the catched exception: the code snipped bit out of context. In some situations it‘s totally fine to catch and not rethrow the exception.

[thomasgalliker]

@HaileyKim04 are you using AppShell or classic navigation? If you find the time to create a small repro app which causes this issue, I‘d be very happy.

[HaileyKim04]

Yes, I am using classic navigation. This is the repository, and I noticed that scanning stops after scanning several barocdes in the repository.

MauiApp1.zip

[Magnuskeel]

Hi , just want to say amazing barcode scanning control, unfortunately I am having the same issue:

CameraScanner.Maui.BarcodeAnalyzer: Error: Analyze failed with exception

System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'AndroidX.Camera.View.Transform.CoordinateTransform'.
at Java.Interop.JniPeerMembers.AssertSelf(IJavaPeerable self) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.cs:line 153
at Java.Interop.JniPeerMembers.JniInstanceMethods.InvokeAbstractVoidMethod(String encodedMember, IJavaPeerable self, JniArgumentValue* parameters) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods_Invoke.cs:line 39
at AndroidX.Camera.View.Transform.CoordinateTransform.MapRect(RectF rect) in D:\a_work\1\s\generated\androidx.camera.camera-view\obj\Release
et8.0-android\generated\src\AndroidX.Camera.View.Transform.CoordinateTransform.cs:line 112
at CameraScanner.Maui.Platforms.Services.BarcodeScanner.ProcessBarcodeResult(Object inputResults, HashSet1 outputResults, CoordinateTransform transform) in C:\Users\mkoso\source\repos\CameraScanner.Maui\Platforms\Android\Services\BarcodeScanner.cs:line 111 at CameraScanner.Maui.CameraManager.PerformBarcodeDetectionAsync(IImageProxy proxy) in C:\Users\mkoso\source\repos\CameraScanner.Maui\Platforms\Android\CameraManager.cs:line 404 at CameraScanner.Maui.Utils.SyncHelper.RunOnceAsync(Func1 task) in C:\Users\mkoso\source\repos\CameraScanner.Maui\Utils\SyncHelper.cs:line 19
at CameraScanner.Maui.BarcodeAnalyzer.Analyze(IImageProxy proxyImage) in C:\Users\mkoso\source\repos\CameraScanner.Maui\Platforms\Android\BarcodeAnalyzer.cs:line 62
[0:] CameraScanner.Maui.BarcodeAnalyzer: Error: Analyze -> IImageProxy.Close failed with exception

System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'AndroidX.Camera.Core.SettableImageProxy'.
at Java.Interop.JniPeerMembers.AssertSelf(IJavaPeerable self) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.cs:line 153
at Java.Interop.JniPeerMembers.JniInstanceMethods.InvokeVirtualVoidMethod(String encodedMember, IJavaPeerable self, JniArgumentValue* parameters) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods_Invoke.cs:line 57
at AndroidX.Camera.Core.ForwardingImageProxy.Close()
at CameraScanner.Maui.BarcodeAnalyzer.Analyze(IImageProxy proxyImage) in C:\Users\mkoso\source\repos\CameraScanner.Maui\Platforms\Android\BarcodeAnalyzer.cs:line 88

I am using AppShell navigation

[thomasgalliker]

Thanks for reporting 👍🏻 I'm currently bit in pre-release stress but I'm positive we can solve this.

[thomasgalliker]

Is it possible to reproduce with the sample app in this repository? Or can anyone create a super-small sample app which causes this issue?

[Magnuskeel]

Not sure yet but might have found a fix, when i am confident its actually working consistently I can show you what I did. Prolly a threading issue.

[Magnuskeel]

I think because the Analyze method was set to async void along with this line

var run = await this.syncHelper.RunOnceAsync(() => this.cameraManager.PerformBarcodeDetectionAsync(proxyImage));

you were getting a race condition.

if you remove the async from the method signature and wrap that above line of code a Task.Run like this:

Task.Run(async () =>
{
    var run = await this.syncHelper.RunOnceAsync(() => this.cameraManager.PerformBarcodeDetectionAsync(proxyImage));

    if (run == false)
    {
        // this.logger.LogDebug("Analyze -> frame skipped (already in progress)");
    }
}).Wait();   

The problem seems to stop happening.

so the entire method looks like this.

```

public void Analyze(IImageProxy proxyImage)
{

    try
    {                   

        if (this.PauseScanning)
        {
            return;
        }

        if (this.BarcodeDetectionFrameRate is not uint r || r is 0u or 1u || this.skippedFrames == null || ++this.skippedFrames >= r)
        {
            // this.logger.LogDebug("Analyze");

            if (this.cameraManager.CaptureNextFrame)
            {
                this.cameraManager.CaptureImage(proxyImage);
            }
            else
            {
                Task.Run(async () =>
                {
                    var run = await this.syncHelper.RunOnceAsync(() => this.cameraManager.PerformBarcodeDetectionAsync(proxyImage));

                    if (run == false)
                    {
                        // this.logger.LogDebug("Analyze -> frame skipped (already in progress)");
                    }
                }).Wait();                        
            }

            if (this.BarcodeDetectionFrameRate != null)
            {
                this.skippedFrames = 0;
            }
        }
        else
        {
            // this.logger.LogDebug("Analyze -> frame skipped (BarcodeDetectionFrameRate)");
        }
    }
    catch (Exception ex)
    {
        this.logger.LogError(ex, "Analyze failed with exception");
    }
    finally
    {
        try
        {
            if(proxyImage != null)
                proxyImage.Close();
        }
        catch (Exception ex)
        {
            this.logger.LogError(ex, "Analyze -> IImageProxy.Close failed with exception");
             MainThread.BeginInvokeOnMainThread(() => this.cameraManager.StartAsync());
        }                
    }            
}

}

And there doesnt seem to be a performance hit. Do with it what you will :)

[haeun159951]

Is it possible to reproduce with the sample app in this repository? Or can anyone create a super-small sample app which causes this issue?

Yes, I could reproduce this error in the sample demo app.

One strange thing is I cannot reproduce the issue in sample as long as the library Project is referenced in the Sample project.
If I remove the library project reference and add the Nuget version, no matter which version, try the latest, pre-release, and 1.3 as well, I can reproduce the issue in the sample project.

I used the QR code scanner page and ViewModel to edit the code.

Steps to produce:

1. Create one barcode using the barcode generator website
2. Scan a barcode and Keep scrolling up and down fast
3. after 2-3 mins, try to check logs to see the exception in console tab

**QrCodeScannerPage.xaml** 
 
<c:CameraView
            Grid.Row="0"
            CameraEnabled="{Binding IsScannerEnabled}"
            OnDetectionFinishedCommand="{Binding OnDetectionFinishedCommand}"/>

        <Label BackgroundColor="White" 
               TextColor="Black"
               WidthRequest="200" Height="80" Text="{Binding ScannedText}"/>

**QrCodeScannerViewModel.cs**
 
   private async Task HandleScanResultAsync(BarcodeResult[] barcodeResults)
        {
            try
            {
                if (barcodeResults.FirstOrDefault() is BarcodeResult barcodeResult)
                {
                    // this.IsScannerPause = true;
                    //
                    // var stop = await this.dialogService.DisplayAlertAsync(
                    //     "Barcode found",
                    //     $"BarcodeType=\"{barcodeResult.BarcodeType}\"{Environment.NewLine}" +
                    //     $"BarcodeFormat=\"{barcodeResult.BarcodeFormat}\"{Environment.NewLine}" +
                    //     $"DisplayValue=\"{barcodeResult.DisplayValue}\"",
                    //     "Stop", "Continue");
                    //
                    // if (stop)
                    // {
                    //     this.StopCamera();
                    // }
                    // else
                    // {
                    //     this.IsScannerPause = false;
                    // }

                    this.ScannedText = barcodeResult.DisplayValue;
                }
            }

[haeun159951]

I think because the Analyze method was set to async void along with this line

var run = await this.syncHelper.RunOnceAsync(() => this.cameraManager.PerformBarcodeDetectionAsync(proxyImage));

you were getting a race condition.

if you remove the async from the method signature and wrap that above line of code a Task.Run like this:

Task.Run(async () =>
{
    var run = await this.syncHelper.RunOnceAsync(() => this.cameraManager.PerformBarcodeDetectionAsync(proxyImage));

    if (run == false)
    {
        // this.logger.LogDebug("Analyze -> frame skipped (already in progress)");
    }
}).Wait();   

The problem seems to stop happening.

so the entire method looks like this.

public void Analyze(IImageProxy proxyImage) {

try
{                   

    if (this.PauseScanning)
    {
        return;
    }

    if (this.BarcodeDetectionFrameRate is not uint r || r is 0u or 1u || this.skippedFrames == null || ++this.skippedFrames >= r)
    {
        // this.logger.LogDebug("Analyze");

        if (this.cameraManager.CaptureNextFrame)
        {
            this.cameraManager.CaptureImage(proxyImage);
        }
        else
        {
            Task.Run(async () =>
            {
                var run = await this.syncHelper.RunOnceAsync(() => this.cameraManager.PerformBarcodeDetectionAsync(proxyImage));

                if (run == false)
                {
                    // this.logger.LogDebug("Analyze -> frame skipped (already in progress)");
                }
            }).Wait();                        
        }

        if (this.BarcodeDetectionFrameRate != null)
        {
            this.skippedFrames = 0;
        }
    }
    else
    {
        // this.logger.LogDebug("Analyze -> frame skipped (BarcodeDetectionFrameRate)");
    }
}
catch (Exception ex)
{
    this.logger.LogError(ex, "Analyze failed with exception");
}
finally
{
    try
    {
        if(proxyImage != null)
            proxyImage.Close();
    }
    catch (Exception ex)
    {
        this.logger.LogError(ex, "Analyze -> IImageProxy.Close failed with exception");
         MainThread.BeginInvokeOnMainThread(() => this.cameraManager.StartAsync());
    }                
}            

}

}

And there doesnt seem to be a performance hit. Do with it what you will :)

I usually get these three exceptions very quickly in logs, but after applying this code, they are now hard to reproduce. No UI freezing issue so far.

Exceptions:

Cannot access a disposed object. Object name: 'AndroidX.Camera.Core.SettableImageProxy'.
Cannot access a disposed object. Object name: 'AndroidX.Camera.View.Transform.CoordinateTransform'.

Would it be possible to create a PR for this fix and publish a new version?

[thomasgalliker]

Ok. I gonna have a look at this code. On which devices did you have the UI freezes?

[haeun159951]

Ok. I gonna have a look at this code. On which devices did you have the UI freezes?

I’ve tried two different devices: a Samsung S21 and an A15. Sometimes, I can reproduce the UI freeze, but not always. Also, the scanning stopped working, and I got the exception: 'Cannot access a disposed object. Object name: 'AndroidX.Camera.Core.SettableImageProxy'

[decv86]

@thomasgalliker Despite the bugs, this is the best plugin at the moment. Thanks for your work!

[thomasgalliker]

We‘re using this plugin in production apps. And yes we also experience the ObjectDisposedException. Sadly there are even worse problems I have to care about. I‘ll come back to this.