Cannot call IVirtualButtonEventHandler Vuforia 5.0.10 - unity3d

Question

Im using Unity 4.7.0 and Vuforia 5.0.10, i cannot call the IVirtualButtonEventHandler.
using UnityEngine;
using System.Collections;
public class VBEventHandler : MonoBehaviour, IVirtualButtonEventHandler
{
}

Answer 1

I just came across this, hope you're still using Unity & Vuforia. You need to add using Vuforia to make the call.
using UnityEngine;
using System.Collections;
using Vuforia;

Answer 2

Register the Virtual Button:
To add a virtual button to an image target, add the VirtualButton element and its attributes to the ImageTarget element in the .xml file.
XML Attributes:
Name - a unique name for the button
Rectangle - defined by the four corners of the rectangle in the
target's coordinate space
Enabled - a boolean indicating whether the button should be enabled
by default
Sensitivity - HIGH, MEDIUM, LOW sensitivity to occlusion
After Registering Virtual Button Code is simple then:
using UnityEngine;
using System.Collections;
using Vuforia;
public class Custom_VirtualButton : MonoBehaviour, IVirtualButtonEventHandler
{
// Use this for initialization
void Start () {
// here it finds any VirtualButton Attached to the ImageTarget and register it's event handler and in the
//OnButtonPressed and OnButtonReleased methods you can handle different buttons Click state
//via "vb.VirtualButtonName" variable and do some really awesome stuff with it.
VirtualButtonBehaviour[] vbs = GetComponentsInChildren<VirtualButtonBehaviour>();
foreach (VirtualButtonBehaviour item in vbs)
{
item.RegisterEventHandler(this);
}
}
// Update is called once per frame
void Update () {
}
#region VirtualButton
public void OnButtonPressed(VirtualButtonAbstractBehaviour vb)
{
Debug.Log("Helllllloooooooooo");
}
public void OnButtonReleased(VirtualButtonAbstractBehaviour vb)
{
Debug.Log("Goooooodbyeeee");
}
#endregion //VirtualButton
}