在iPhone上打开手电筒/闪光灯

我知道，打开闪光灯并将其保持在iPhone 4上的唯一方法是打开摄像机。我不太确定代码。这是我正在尝试的：

-(IBAction)turnTorchOn {
    AVCaptureSession *captureSession = [[AVCaptureSession alloc] init];
    AVCaptureDevice *videoCaptureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    NSError *error = nil;
    AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoCaptureDevice error:&error];

    if (videoInput) {
        [captureSession addInput:videoInput];

        AVCaptureVideoDataOutput* videoOutput = [[AVCaptureVideoDataOutput alloc] init];
        [videoOutput setSampleBufferDelegate:self queue:dispatch_get_current_queue()];

        [captureSession addOutput:videoOutput];

        [captureSession startRunning];

        videoCaptureDevice.torchMode = AVCaptureTorchModeOn;
    }   
}

有人知道这是否行得通吗？（我还没有要测试的iPhone 4-只是尝试一些新的API）。

谢谢