我正在xamarin.forms应用程序中实现扫描仪功能，为此，我正在使用iOS本机AVCaptureSession。但是我的问题是在扫描或捕获 session 处于 Activity 状态并且设备被锁定时，然后在解锁设备后冻结捕获 session ，这很奇怪。
我尝试使用UIApplication.DidEnterBackgroundNotification | UIApplication.WillEnterForegroundNotification处理它，在此我停止并再次启动捕获 session 。但是冻结仍在发生。
using System;
using AVFoundation;
using CoreFoundation;
using CoreGraphics;
using Foundation;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
namespace MarginPointApp.iOS
{
public class ScannerViewController : UIViewController
{
AVCaptureDevice captureDevice;
AVCaptureVideoPreviewLayer videoPreviewLayer;
AVCaptureSession captureSession;
UIView viewfinderView;
MetadataObjectsDelegate metadataObjectsDelegate;
public event EventHandler<String> OnScanSuccess;
UIView redLineCenter;
UIView overlayView;
UIView overlay;
UIView bottomBarView;
UIButton flashLightButton;
UIButton cancelButton;
UIButton cameraButton;
UILabel bottomTextLabel;
bool isCameraDismissed;
NSObject interuptStartNoti, interuptEndNoti;
AVMetadataObjectType metaTypes = AVMetadataObjectType.Code128Code |
AVMetadataObjectType.Code39Code | AVMetadataObjectType.Code39Mod43Code |
AVMetadataObjectType.DataMatrixCode | AVMetadataObjectType.EAN13Code | AVMetadataObjectType.EAN8Code |
AVMetadataObjectType.Interleaved2of5Code | AVMetadataObjectType.PDF417Code |
AVMetadataObjectType.QRCode | AVMetadataObjectType.UPCECode;
public override void ViewDidLoad()
{
base.ViewDidLoad();
UIView statusBar = UIApplication.SharedApplication.ValueForKey(new NSString("statusBar")) as UIView;
if (statusBar.RespondsToSelector(new ObjCRuntime.Selector("setBackgroundColor:")))
{
statusBar.BackgroundColor = UIColor.Black;
}
NavigationItem.Title = "Scanner";
this.View.BackgroundColor = UIColor.White;
if (marginpoint.im.iOS.AppDelegate.camPosition)
{
captureDevice = GetCameraDevice(AVCaptureDevicePosition.Front);
}
else
{
captureDevice = GetCameraDevice(AVCaptureDevicePosition.Back);
}
CameraSetup();
}
public void CameraSetup()
{
NSError error = null;
if (captureDevice != null)
{
try
{
var input = new AVCaptureDeviceInput(captureDevice, out error);
captureSession = new AVCaptureSession();
if (captureSession == null) { return; }
if (captureSession.CanAddInput(input))
captureSession.AddInput(input);
var captureMetadataOutput = new AVCaptureMetadataOutput();
if (captureSession.CanAddOutput(captureMetadataOutput))
{
captureSession.AddOutput(captureMetadataOutput);
// captureMetadataOutput.MetadataObjectTypes = captureMetadataOutput.AvailableMetadataObjectTypes;
captureMetadataOutput.MetadataObjectTypes = metaTypes;
}
var metadataQueue = new DispatchQueue("com.AVCam.metadata");
metadataObjectsDelegate = new MetadataObjectsDelegate
{
DidOutputMetadataObjectsAction = DidOutputMetadataObjects
};
captureMetadataOutput.SetDelegate(metadataObjectsDelegate, metadataQueue);
videoPreviewLayer = new AVCaptureVideoPreviewLayer(session: captureSession);
videoPreviewLayer.VideoGravity = AVLayerVideoGravity.ResizeAspectFill;
videoPreviewLayer.Frame = View.Layer.Bounds;
View.Layer.AddSublayer(videoPreviewLayer);
}
catch (Exception e)
{
//Console.WriteLine("error device input" + e.ToString());
}
}
// Prepare device for configuration
captureDevice.LockForConfiguration(out error);
if (error != null)
{
// There has been an issue, abort
//Console.WriteLine("Error: {0}", error.LocalizedDescription);
captureDevice.UnlockForConfiguration();
return;
}
addOverlayOnScreen();
/*
string reason = string.Empty;
if (interuptStartNoti == null)
{
interuptStartNoti = AVCaptureSession.Notifications.ObserveWasInterrupted((sender, e) =>
{
reason = e.Notification.UserInfo?.ValueForKey(new NSString("AVCaptureSessionInterruptionReasonKey"))?.ToString();
if (captureSession != null && !reason.Equals(string.Empty) && !reason.Equals("3"))
{
captureSession.StopRunning();
//captureSession.Dispose();
//captureSession = null;
}
});
}
if (interuptEndNoti == null)
{
interuptEndNoti = AVCaptureSession.Notifications.ObserveInterruptionEnded((sender, e) =>
{
Device.BeginInvokeOnMainThread(() =>
{
if (marginpoint.im.iOS.AppDelegate.camPosition)
{
captureDevice = GetCameraDevice(AVCaptureDevicePosition.Front);
}
else
{
captureDevice = GetCameraDevice(AVCaptureDevicePosition.Back);
}
if (!reason.Equals(string.Empty) && !reason.Equals("3"))
{
//CameraSetup();
captureSession.StartRunning();
}
});
});
}
*/
}
NSObject didEnterBackgroundNoti, willEnterForegroundNoti;
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
if (didEnterBackgroundNoti == null)
{
didEnterBackgroundNoti = NSNotificationCenter.DefaultCenter.AddObserver(UIApplication.DidEnterBackgroundNotification, (obj) =>
{
Device.BeginInvokeOnMainThread(() =>
{
AddBlurEffect();
captureSession?.StopRunning();
});
});
}
willEnterForegroundNoti = NSNotificationCenter.DefaultCenter.AddObserver(UIApplication.WillEnterForegroundNotification, (obj) =>
{
Device.BeginInvokeOnMainThread(() =>
{
RemoveBlurEffect();
CameraSetup();
});
});
}
public override void ViewWillDisappear(bool animated)
{
base.ViewWillDisappear(animated);
NSNotificationCenter.DefaultCenter.RemoveObserver(didEnterBackgroundNoti);
NSNotificationCenter.DefaultCenter.RemoveObserver(willEnterForegroundNoti);
}
private AVCaptureDevice GetCameraDevice(AVCaptureDevicePosition position)
{
AVCaptureDevice captureDevice = null;
if (UIDevice.CurrentDevice.CheckSystemVersion(10, 0))
{
captureDevice = AVCaptureDevice.GetDefaultDevice(AVCaptureDeviceType.BuiltInWideAngleCamera, AVMediaType.Video, position);//AVCaptureDevice.GetDefaultDevice(AVMediaTypes.Video);
}
else
{
var devices = AVCaptureDevice.DevicesWithMediaType(AVMediaType.Video);
foreach (var device in devices)
{
if (device.Position == position)
{
captureDevice = device;
}
}
}
return captureDevice;
}
UIVisualEffectView blurView;
/// <summary>
/// Adds the blur effect to camera preview.
/// </summary>
void AddBlurEffect()
{
if (blurView == null)
{
var blur = UIBlurEffect.FromStyle(UIBlurEffectStyle.Light);
blurView = new UIVisualEffectView(blur);
blurView.Frame = View.Frame;
blurView.AutoresizingMask = UIViewAutoresizing.FlexibleHeight | UIViewAutoresizing.FlexibleWidth;
View.AddSubview(blurView);
}
}
void RemoveBlurEffect()
{
if (blurView != null)
{
blurView.RemoveFromSuperview();
blurView = null;
}
}
void addOverlayOnScreen()
{
overlayView = new UIView();
overlayView.Frame = new CGRect(x: 0, y: 0, width: View.Frame.Width, height: View.Frame.Height);
View.AddSubview(overlayView);
View.BringSubviewToFront(overlayView);
var overlayWidth = Application.Current.MainPage.Width * 0.7;
overlay = new UIView();
overlay.Layer.BorderColor = UIColor.Green.CGColor;
overlay.Layer.BorderWidth = 4;
overlay.Frame = new CGRect(x: View.Center.X - overlayWidth / 2, y: View.Center.Y - overlayWidth / 2, width: overlayWidth, height: overlayWidth);
overlayView.AddSubview(overlay);
overlayView.BringSubviewToFront(overlay);
redLineCenter = new UIView();
redLineCenter.BackgroundColor = UIColor.Red;
redLineCenter.Alpha = 0.5f;
redLineCenter.Frame = new CGRect(x: overlay.Frame.X + 4, y: overlay.Center.Y - 2, width: overlay.Frame.Width - 9, height: 4);
overlayView.AddSubview(redLineCenter);
overlayView.BringSubviewToFront(redLineCenter);
// to find Qr code
viewfinderView = new UIView();
viewfinderView.Frame = new CGRect(x: overlay.Frame.X, y: overlay.Center.Y - 50, width: overlay.Frame.Width, height: 100);
overlayView.AddSubview(viewfinderView);
overlayView.BringSubviewToFront(viewfinderView);
bottomBarView = new UIView();
bottomBarView.BackgroundColor = UIColor.White;
bottomBarView.Frame = new CGRect(x: 0, y: View.Frame.Height - 50, width: View.Frame.Width, height: 50);
overlayView.AddSubview(bottomBarView);
overlayView.BringSubviewToFront(bottomBarView);
var centerPoint = (bottomBarView.Frame.Top - overlay.Frame.Bottom) / 2 - 15;
bottomTextLabel = new UILabel
{
Frame = new CGRect(x: View.Frame.X, y: overlay.Frame.Bottom + centerPoint, width: View.Frame.Width, height: 30),
Text = AppResources.ScanAutomatically,
TextColor = UIColor.White,
Font = UIFont.FromName("TitilliumWeb-Regular", 17),
TextAlignment = UITextAlignment.Center
};
View.AddSubview(bottomTextLabel);
View.BringSubviewToFront(bottomTextLabel);
if (captureDevice.Position == AVCaptureDevicePosition.Back)
{
flashLightButton = new UIButton();
flashLightButton.SetImage(new UIImage(filename: "flash_white_light.png"), UIControlState.Normal);
flashLightButton.Frame = new CGRect(x: 0, y: 0, width: 50, height: 50);
bottomBarView.AddSubview(flashLightButton);
flashLightButton.TouchUpInside += async (object sender, EventArgs e) =>
{
NSError error = null;
if (captureDevice == null) return;
captureDevice.LockForConfiguration(out error);
if (error != null)
{
captureDevice.UnlockForConfiguration();
return;
}
else
{
if (!captureDevice.TorchAvailable)
{
var alert = new UIAlertView
{
Title = AppResources.MarginPoint,
Message = AppResources.CameraFlash
};
alert.AddButton(AppResources.OkButtonTitle);
alert.Show();
return;
}
if (captureDevice.TorchMode != AVCaptureTorchMode.On)
{
captureDevice.TorchMode = AVCaptureTorchMode.On;
}
else
{
captureDevice.TorchMode = AVCaptureTorchMode.Off;
}
captureDevice.UnlockForConfiguration();
}
};
}
string blueColor = "#1273B6";
cancelButton = new UIButton();
cancelButton.SetTitleColor(Color.FromHex(blueColor).ToUIColor(), UIControlState.Normal);
cancelButton.SetTitle(AppResources.PickerCancelLabel, UIControlState.Normal);
cancelButton.Font = UIFont.FromName("TitilliumWeb-Regular", 18);
cancelButton.Frame = new CGRect(x: bottomBarView.Center.X - 50, y: 0, width: 100, height: 50);
bottomBarView.AddSubview(cancelButton);
cancelButton.TouchUpInside += (object sender, EventArgs e) =>
{
if (captureSession != null)
captureSession.StopRunning();
DismissViewController(true, null);
};
Device.BeginInvokeOnMainThread(() =>
{
if (captureSession != null)
captureSession.StartRunning();
});
cameraButton = new UIButton();
cameraButton.SetImage(new UIImage(filename: "camera.png"), UIControlState.Normal);
cameraButton.Frame = new CGRect(x: bottomBarView.Frame.Width - 50, y: 0, width: 50, height: 50);
bottomBarView.AddSubview(cameraButton);
cameraButton.TouchUpInside += (object sender, EventArgs e) =>
{
if (captureDevice.Position == AVCaptureDevicePosition.Back)
{
if (captureDevice.TorchAvailable)
captureDevice.TorchMode = AVCaptureTorchMode.Off;
captureDevice = GetCameraDevice(AVCaptureDevicePosition.Front);
marginpoint.im.iOS.AppDelegate.camPosition = true;
}
else
{
if (captureDevice.TorchAvailable)
captureDevice.TorchMode = AVCaptureTorchMode.Off;
captureDevice = GetCameraDevice(AVCaptureDevicePosition.Back);
marginpoint.im.iOS.AppDelegate.camPosition = false;
}
if (captureDevice != null)
{
try
{
NSError error;
var input = new AVCaptureDeviceInput(captureDevice, out error);
captureSession = new AVCaptureSession();
if (captureSession == null) { return; }
if (captureSession.CanAddInput(input))
captureSession.AddInput(input);
var captureMetadataOutput = new AVCaptureMetadataOutput();
if (captureSession.CanAddOutput(captureMetadataOutput))
{
captureSession.AddOutput(captureMetadataOutput);
// captureMetadataOutput.MetadataObjectTypes = captureMetadataOutput.AvailableMetadataObjectTypes;
captureMetadataOutput.MetadataObjectTypes = metaTypes;
}
var metadataQueue = new DispatchQueue("com.AVCam.metadata");
metadataObjectsDelegate = new MetadataObjectsDelegate
{
DidOutputMetadataObjectsAction = DidOutputMetadataObjects
};
captureMetadataOutput.SetDelegate(metadataObjectsDelegate, metadataQueue);
captureSession.StartRunning();
videoPreviewLayer = new AVCaptureVideoPreviewLayer(session: captureSession);
videoPreviewLayer.VideoGravity = AVLayerVideoGravity.ResizeAspectFill;
videoPreviewLayer.Frame = View.Layer.Bounds;
View.Layer.AddSublayer(videoPreviewLayer);
}
catch (Exception ex)
{
// Console.WriteLine("error device input" + ex.ToString());
}
addOverlayOnScreen();
}
};
}
public void DidOutputMetadataObjects(AVCaptureOutput captureOutput,
AVMetadataObject[] metadataObjects,
AVCaptureConnection connection)
{
Device.BeginInvokeOnMainThread(() =>
{
if (metadataObjects != null && metadataObjects.Length == 0)
{
//codeLabel.Text = "No Data";
//displayScanResult(string.Empty);
return;
}
var metadataObject = metadataObjects[0] as AVMetadataMachineReadableCodeObject;
if (metadataObject == null) { return; }
var visualCodeObject = videoPreviewLayer.GetTransformedMetadataObject(metadataObject);
if (metadataObject.Type == AVMetadataObjectType.QRCode)
{
if (viewfinderView.Frame.Contains(visualCodeObject.Bounds))
{
captureSession.StopRunning();
displayScanResult(metadataObject.StringValue);
}
}
else
{
captureSession.StopRunning();
displayScanResult(metadataObject.StringValue);
}
});
}
private async void displayScanResult(string metadataObjectVal)
{
OnScanSuccess?.Invoke(this, string.IsNullOrWhiteSpace(metadataObjectVal) ? string.Empty : metadataObjectVal as String);
captureSession.StopRunning();
DismissViewController(true, null);
//codeLabel.Text = metadataObject.StringValue;
}
}
class MetadataObjectsDelegate : AVCaptureMetadataOutputObjectsDelegate
{
public Action<AVCaptureMetadataOutput, AVMetadataObject[], AVCaptureConnection> DidOutputMetadataObjectsAction;
public override void DidOutputMetadataObjects(AVCaptureMetadataOutput captureOutput, AVMetadataObject[] metadataObjects, AVCaptureConnection connection)
{
if (DidOutputMetadataObjectsAction != null)
DidOutputMetadataObjectsAction(captureOutput, metadataObjects, connection);
}
}
}
有没有人遇到这个问题并找到解决方法？
最佳答案
与其在用户进入前景时每次都创建新的captureSession，不如尝试仅启动现有的captureSession。
willEnterForegroundNoti =
NSNotificationCenter.DefaultCenter.AddObserver(UIApplication.WillEnterForegroundNotification,
(obj) => {
Device.BeginInvokeOnMainThread(() => {
RemoveBlurEffect();
captureSession?.startRunning();
});
});