- (void)getTorch {  AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];  AVCaptureDeviceInput *input = [[AVCaptureDeviceInput alloc]initWithDevice:device error:nil];  AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];  [output setSampleBufferDelegate:self queue:dispatch_get_main_queue()];  self.session = [[AVCaptureSession alloc]init];  [self.session setSessionPreset:AVCaptureSessionPresetHigh];  if ([self.session canAddInput:input]) {    [self.session addInput:input];  }  if ([self.session canAddOutput:output]) {    [self.session addOutput:output];  }  [self.session startRunning];}- (void)captureOutput:(AVCaptureOutput*)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection {  CFDictionaryRef metadataDict =CMCopyDictionaryOfAttachments(NULL,sampleBuffer,   kCMAttachmentMode_ShouldPropagate);  NSDictionary *metadata = [[NSMutableDictionary alloc] initWithDictionary:  (__bridgeNSDictionary*)metadataDict];  CFRelease(metadataDict);  NSDictionary *exifMetadata = [[metadata objectForKey:(NSString*)kCGImagePropertyExifDictionary] mutableCopy];  float brightnessValue = [[exifMetadata objectForKey:(NSString*)kCGImagePropertyExifBrightnessValue] floatValue];  NSLog(@"%f",brightnessValue);  // 根據brightnessValue的值來打開和關閉閃光燈  AVCaptureDevice*device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];  BOOL result = [device hasTorch];// 判斷設備是否有閃光燈  if((brightnessValue <0) && result) {  // 打開閃光燈    [device lockForConfiguration:nil];    [device setTorchMode:AVCaptureTorchModeOn];//開    [device unlockForConfiguration];  }else if((brightnessValue >0) && result) {  // 關閉閃光燈    [device lockForConfiguration:nil];        [device setTorchMode:AVCaptureTorchModeOff];//關    [device unlockForConfiguration];    }}