SkeletonStream NullReferenceException was unhandled

我正在尝试从2个Kinect传感器获取骨骼关节的X,Y,Z位置。到目前为止，我有一个简单的形式，2个按钮和6个标签。点击第一个按钮，我想在标签1、2、3中显示右手的x、y、z位置。我也想用第二个按钮，但是用第二个kinect设备。

它在一个Kinect上运行得非常好，但当我为第二个Kinect添加代码时，抛出了NullReferenceException。谁能告诉我我哪里错了?谢谢你。

观察窗口:

sensor.SkeletonStream.Enable ();的传感器。'是null

异常消息:对象引用未设置为对象的实例。

public partial class Form1 : Form
{
     Skeleton[] skeletons;
     Skeleton[] skeletons2;
    public Form1()
    {
        InitializeComponent();
        // First Kinect Device
        KinectSensor sensor = KinectSensor.KinectSensors[0];
        sensor.SkeletonStream.Enable();  // Here is the exception thrown
        sensor.SkeletonFrameReady += new EventHandler<SkeletonFrameReadyEventArgs>(SensorSkeletonFrameReady);
        sensor.Start();
        // Second Kinect Device
        KinectSensor sensor2 = KinectSensor.KinectSensors[1];
        sensor2.SkeletonStream.Enable();
        sensor2.SkeletonFrameReady += new EventHandler<SkeletonFrameReadyEventArgs>(SensorSkeletonFrameReady2);
        sensor2.Start();

    }

    private void SensorSkeletonFrameReady(object sender, SkeletonFrameReadyEventArgs e)
    {
        skeletons = new Skeleton[0];
        using (SkeletonFrame skeletonFrame = e.OpenSkeletonFrame())
        {
            if (skeletonFrame != null)
            {
                skeletons = new Skeleton[skeletonFrame.SkeletonArrayLength];
                skeletonFrame.CopySkeletonDataTo(skeletons);
            }
        }
    }
    private void SensorSkeletonFrameReady2(object sender, SkeletonFrameReadyEventArgs e)
    {
        skeletons2 = new Skeleton[0];
        using (SkeletonFrame skeletonFrame2 = e.OpenSkeletonFrame())
        {
            if (skeletonFrame2 != null)
            {
                skeletons2 = new Skeleton[skeletonFrame2.SkeletonArrayLength];
                skeletonFrame2.CopySkeletonDataTo(skeletons2);
            }
        }
    }
    private void button1_Click(object sender, EventArgs e)
    {
        foreach(Skeleton skeleton in skeletons) 
        {
            // get the joint
            Joint rightHand = skeleton.Joints[JointType.HandRight];
            // get the individual points of the right hand
            double rightX = rightHand.Position.X;
            double rightY = rightHand.Position.Y;
            double rightZ = rightHand.Position.Z;
            label1.Text = rightX.ToString();
            label2.Text = rightY.ToString();
            label3.Text = rightZ.ToString();
        }

    }
    private void button2_Click(object sender, EventArgs e)
    {
        foreach (Skeleton skeleton in skeletons2)
        {
            // get the joint
            Joint rightHand = skeleton.Joints[JointType.HandRight];
            // get the individual points of the right hand
            double rightX = rightHand.Position.X;
            double rightY = rightHand.Position.Y;
            double rightZ = rightHand.Position.Z;
            label4.Text = rightX.ToString();
            label5.Text = rightY.ToString();
            label6.Text = rightZ.ToString();
        }
    }

}