How to set up event handling with prebuild class

Question

I am very new to C# and try to use Microsoft.MixedReality.QR for reading some QRCodes with the Hololense 2 and have problems accessing the events of the QRCodeWatcher. According to the API, the QRCodeWatcher class has 4 events but it seems that these are never triggered. (QR_Added, QR_Updated,... are never called). Am I setting up something wrong?

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Microsoft.MixedReality.QR;
using QRTracking;
namespace QRTracking {
  public class Detector: MonoBehaviour {

    public TextMesh debugScreen;
    public bool IsSupported {get; private set;  }
    private QRCodeWatcher qrTracker;
    private bool QRstarted=false;
    private QRCodeWatcherAccessStatus accessStatus;

    // Start is called before the first frame update
    async protected virtual void Start() {
      debugScreen.text="Hello";
      if (QRCodeWatcher.IsSupported()) {
        try {
          accessStatus=await QRCodeWatcher.RequestAccessAsync();
          debugScreen.text=accessStatus.ToString();
        }
        catch {
          debugScreen.text="No World";
        }
      }
    }

    // Update is called once per frame
    void Update() {
      if (accessStatus.ToString()=="Allowed") {
        if (QRstarted==false) {
          debugScreen.text="Setup Tracking";
          SetupQRTracking();
          QRstarted=true;
        }
      }
    }

    private void SetupQRTracking() {
      qrTracker=new QRCodeWatcher();
      qrTracker.Added+=QR_Added;
      qrTracker.Updated+=QR_Updated;
      qrTracker.Removed+=QR_Removed;
      qrTracker.EnumerationCompleted+=QR_Enum;
      qrTracker.Start();
      debugScreen.text="Tracking started";
    }

    private void QR_Added(object sender, QRCodeAddedEventArgs args) {
      debugScreen.text="Added";
    }
    private void QR_Updated(object sender, QRCodeUpdatedEventArgs args) {
      debugScreen.text="Updated";
    }
    private void QR_Removed(object sender, QRCodeRemovedEventArgs args) {
      debugScreen.text="Removed";
    }
    private void QR_Enum(object sender, object e) {
      debugScreen.text="Enum";
    }
  }
}

(While the script is running the HoloLense is able to read the content of a QRCode. The debugScreen is a TextMesh so that I can see the text while wearing the HoloLense.)

Answer 1

Workaround to get only the recently seen QR codes to mimic the update event:

private IReadOnlyList<QRCode> detectedQR;    
private DateTimeOffset timestamp;
private int timetolerance = 1; // seconds

detectedQR = qrTracker.GetList();
timestamp = DateTimeOffset.Now;
foreach (var QR in detectedQR)
  {if ((timestamp  - QR.LastDetectedTime ).Duration() < TimeSpan.FromSeconds(timetolerance))
     {
       //Do stuff with QR Codes seen in the last second
     }
  }

However, with too many QR codes, performance could suffer.

Answer 2

Hi I’m Wayne Wang from the Microsoft for Founders Hub team!

We do have an example from my colleague on your current context.

Seems the implementation you may need is here: https://github.com/chgatla-microsoft/QRTracking/blob/master/SampleQRCodes/Assets/Scripts/QRCodesManager.cs

it was little bit of old but I believe the Interfaces and pipelines still the same