iOS正确停止AVCaptureSession

Question

我在iOS 7中测试新的条形码扫描api时出了问题.这个例子(单视图应用程序)工作正常,但我想停止AVCaptureSession并在摄像机识别出EAN代码后显示第一个视图.

[self.captureSession startRunning]; 不起作用.

我如何正确停止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

你可以实际上停止AVCaptureSession:

[self.captureSession stopRunning];

但我怀疑你真正想做的是冻结屏幕.在属性中保留对previewLayer的引用很有帮助.然后:

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

您可以尝试这样的方法来冻结屏幕,然后在几秒钟后将其解冻

- (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;