iOS 正确停止 AVCaptureSession

Question

我在 iOS 7 中测试新的条形码扫描 api 时遇到问题。这个示例(单 View 应用程序)工作正常，但我想停止 AVCaptureSession 并在相机识别 EAN 代码后显示第一个 View 。

[self.captureSession startRunning]; 不起作用。

如何正确停止 AVCaptureSession？

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>

@interface ViewController ()  <AVCaptureMetadataOutputObjectsDelegate>

@property (strong) AVCaptureSession *captureSession;

@end

@implementation ViewController


- (void)viewDidLoad
{
    [super viewDidLoad];
    self.captureSession = [[AVCaptureSession alloc] init];
    AVCaptureDevice *videoCaptureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    NSError *error = nil;
    AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoCaptureDevice error:&error];
    if(videoInput)
        [self.captureSession addInput:videoInput];
    else
        NSLog(@"Error: %@", error);

    AVCaptureMetadataOutput *metadataOutput = [[AVCaptureMetadataOutput alloc] init];
    [self.captureSession addOutput:metadataOutput];
    [metadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    [metadataOutput setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode, AVMetadataObjectTypeEAN13Code]];

    AVCaptureVideoPreviewLayer *previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.captureSession];
    previewLayer.frame = self.view.layer.bounds;
    [self.view.layer addSublayer:previewLayer];

    [self.captureSession startRunning];

}

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
    for(AVMetadataObject *metadataObject in metadataObjects)
    {
        AVMetadataMachineReadableCodeObject *readableObject = (AVMetadataMachineReadableCodeObject *)metadataObject;
        if([metadataObject.type isEqualToString:AVMetadataObjectTypeQRCode])
        {
            NSLog(@"QR Code = %@", readableObject.stringValue);
        }
        else if ([metadataObject.type isEqualToString:AVMetadataObjectTypeEAN13Code])
        {
            NSLog(@"EAN 13 = %@", readableObject.stringValue);



        }
    }
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

Answer 1

您实际上可以这样停止 AVCaptureSession:

[self.captureSession stopRunning];

但我怀疑您真正想要做的是卡住屏幕。在属性中保留对 previewLayer 的引用很有帮助。然后:

[[self.previewLayer connection] setEnabled:NO];

你可以尝试这样的方法来卡住屏幕，然后在几秒钟后解冻

- (void)     captureOutput:(AVCaptureOutput *)captureOutput 
  didOutputMetadataObjects:(NSArray *)metadataObjects 
            fromConnection:(AVCaptureConnection *)connection
{   
    [[self.previewLayer connection] setEnabled:NO];

    double delayInSeconds = 2.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 
                                  (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        [[self.previewLayer connection] setEnabled:YES];

    });

    ...

}

更新
完全删除:

[self.captureSession stopRunning];
[self.previewLayer removeFromSuperlayer];
self.previewLayer = nil;
self.captureSession = nil;