从条形码扫描视图导航回时，将为共享资源释放实例

本文关键字：共享资源 释放 实例 扫描 条形码 视图 导航 | 更新日期: 2023-09-27 18:29:15

我的应用程序中有条形码扫描功能。主页面上有一个条形码按钮，用户点击该按钮后进入条形码扫描页面。但当它导航回来时，我收到一个消息框，上面写着：

This instance has been disposed. Possibly because another component required a shared resource.

我处理了PhotoCamera，并取消了条形码扫描页面上OnNavigatedFrom方法中的所有事件，但仍然得到了相同的结果。

我进入代码，发现这个方法有问题：

PhotoCamera _cam;
VideoBrush _videoBrush = new VideoBrush();
Stopwatch watch = new Stopwatch();
int _nbTry;
Result result = null;
void cam_AutoFocusCompleted(object sender, CameraOperationCompletedEventArgs e)
        {
            if (result == null)
            { 
            try
            {
                _nbTry++;
                watch.Reset();
                watch.Start();
                while ((result == null) && (watch.ElapsedMilliseconds < 1500) && _cam != null)
                {
                    var binaryBitmap = GetBitmapFromVideo(_cam);
                    if (binaryBitmap != null)
                    {
                        try
                        {
                            result = BarCodeManager.ZXingReader.decode(binaryBitmap);
                        }
                        catch
                        {
                            // Wasn't able to find a barcode
                        }
                    }
                }
                if (result != null)
                {
                    BarCodeManager._onBarCodeFound(result.Text);
                }
                else
                {
                    if (_cam != null)
                    {
                        _cam.Focus();
                    }
                }
            }
            catch (Exception exc)
            {
                BarCodeManager._onError(exc);
            }
        }
      }

有一个异常被捕获，下面是堆栈跟踪：

at Microsoft.Devices.Camera.InvokeAndRemapExceptions(Action a)
at Microsoft.Devices.PhotoCamera.get_IsFocusSupported()
at Microsoft.Devices.PhotoCamera.Focus()
at WP7.ScanBarCode.BarCode.cam_AutoFocusCompleted(Object sender, CameraOperationCompletedEventArgs e)
at Microsoft.Devices.Camera.<>c__DisplayClass21`1.<SafeFireEvent>b__1f(Object ignored)
at System.Threading.ThreadPool.WorkItem.WaitCallback_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadPool.WorkItem.doWork(Object o)
at System.Threading.Timer.ring()

有什么想法吗？谢谢

从条形码扫描视图导航回时，将为共享资源释放实例

第一次离开条形码扫描页面时，您可能会处理PhotoCamera。

如果你只是处理PhotoCamera对象，当你返回条形码扫描页面时，你会得到这个错误：

This instance has been disposed. Possibly because another component required a shared resource.

尝试处理PhotoCamera对象以及所有事件委托，如Initialized或相关：

// Release the camera object:
PhotoCamera.Dispose();
// Remove initialization event:
PhotoCamera.Initialized -= PhotoCamera_Initialized;
// For example, you must remove also the events linked to the camera management (e.g. when you press camera buttons):
CameraButtons.ShutterKeyHalfPressed -= CameraButtons_ShutterKeyHalfPressed;

当您进入条形码扫描页面的OnNavigatedFrom事件时，调用此处置代码，一切都应该正常！

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