The AR app without shadow In my phone

I am so happy for your coming. Then the problem is that I create a AR app，but it didn't show shadow in my phone.I found a solve on the Internet. It say I can attach the following program to the AR Camera.

using UnityEngine;
using System.Collections;
using Vuforia;

public class FixProjectionMatrix : MonoBehaviour, IVideoBackgroundEventHandler
{
private Camera[] mCameras;

// Use this for initialization
void Start()
{
mCameras = VuforiaBehaviour.Instance.GetComponentsInChildren<Camera>();
VuforiaBehaviour.Instance.RegisterVideoBgEventHandler(this);
}

// Update is called once per frame
void Update()
{

}

public void OnVideoBackgroundConfigChanged()
{
foreach (var cam in mCameras)
{
var projMatrix = cam.projectionMatrix;
for (int i = 0; i < 16; i++)
{
if (System.Math.Abs(projMatrix) < 1e-6)
{
projMatrix = 0.0f;
}
}
cam.projectionMatrix = projMatrix;
}
}
}


But unity reports the errors：Type `Vuforia.VuforiaBehaviour' does not contain a definition for `RegisterVideoBgEventHandler' and no extension method `RegisterVideoBgEventHandler' of type `Vuforia.VuforiaBehaviour' could be found. Are you missing an assembly reference?
Did I forget something？I am so Thanksgiving if you can answer my question.