现在好多应有都具备扫码功能，为了减少用户操作，一般会在光线比较暗的时候，自动打开闪光灯：
1、导入头文件
#import <AVFoundation/AVFoundation.h>
#import <ImageIO/ImageIO.h>
2、创建设备、输入输出流
// 1.获取硬件设备
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; // 2.创建输入流
AVCaptureDeviceInput *input = [[AVCaptureDeviceInput alloc]initWithDevice:device error:nil]; // 3.创建设备输出流
AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
[output setSampleBufferDelegate:self queue:dispatch_get_main_queue()]; // AVCaptureSession属性
self.session = [[AVCaptureSession alloc]init];
// 设置为高质量采集率
[self.session setSessionPreset:AVCaptureSessionPresetHigh];
// 添加会话输入和输出
if ([self.session canAddInput:input]) {
[self.session addInput:input];
}
if ([self.session canAddOutput:output]) {
[self.session addOutput:output];
} // 9.启动会话
[self.session startRunning];
3、实现代理方法
#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
CFDictionaryRef metadataDict = CMCopyDictionaryOfAttachments(NULL,sampleBuffer, kCMAttachmentMode_ShouldPropagate);
NSDictionary *metadata = [[NSMutableDictionary alloc] initWithDictionary:(__bridge NSDictionary*)metadataDict];
CFRelease(metadataDict);
NSDictionary *exifMetadata = [[metadata objectForKey:(NSString *)kCGImagePropertyExifDictionary] mutableCopy];
float brightnessValue = [[exifMetadata objectForKey:(NSString *)kCGImagePropertyExifBrightnessValue] floatValue];
// brightnessValue 值代表光线强度，值越小代表光线越暗
if (brightnessValue <= - && !_isAutoOpen) {
_isAutoOpen = YES;
[self.torchBtn setSelected:YES];
[self turnTorchOn:YES];
}
}
4、开启关闭闪光灯
// 打开/关闭手电筒
- (void)turnTorchOn:(BOOL)on{
if ([self.device hasTorch] && [self.device hasFlash]){ [self.device lockForConfiguration:nil];
if (on) {
[self.device setTorchMode:AVCaptureTorchModeOn];
[self.device setFlashMode:AVCaptureFlashModeOn];
} else {
[self.device setTorchMode:AVCaptureTorchModeOff];
[self.device setFlashMode:AVCaptureFlashModeOff];
}
[self.device unlockForConfiguration];
} else {
[SSAlertView showWithTitle:@"提示" message:@"当前设备没有闪光灯，不能提供手电筒功能" commitTitle:@"我知道了" cancelTitle:nil commitAction:nil cancelBlock:nil];
}
}
转自：http://www.cenzhijun.top/2017/07/自动打开闪光灯/