用代码打开IOS设备的闪光灯

 AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

        if (device.torchMode == AVCaptureTorchModeOff) 
        {
                // Create an AV session
                AVCaptureSession *session = [[AVCaptureSession alloc] init];

                // Create device input and add to current session
                AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error: nil];
                [session addInput:input];

                // Create video output and add to current session      
                AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
                [session addOutput:output];

                // Start session configuration
                [session beginConfiguration];
                [device lockForConfiguration:nil];

                // Set torch to on
                [device setTorchMode:AVCaptureTorchModeOn];

                [device unlockForConfiguration];
                [session commitConfiguration];

                // Start the session
                [session startRunning];

                // Keep the session around
                [self setAVSession:session];

                [output release];
        }
        else 
        {
                [AVSession stopRunning];
                [AVSession release], AVSession = nil;
        }