NFC Action_Tech_Discovered with foreground dispatch won't catch Mifare 1k card

Question

I'm coding in C# with Xamarin and trying to scan a MIFARE Classic 1K card by NFC.

The intent-filter of m1card_test is working fine. But I don't want to select which Activity I want to start. So I'm trying to use the foreground dispatch.

Here is part of my code (C#):

• OnCreate

  Intent Myintent = new Intent(this, GetType());
  Myintent.AddFlags(ActivityFlags.SingleTop);
  mPendingIntent = PendingIntent.GetActivity(this, 0, Myintent, 0);
  
  ndefDetected = new IntentFilter(NfcAdapter.ActionTechDiscovered);
  ndefDetected.AddDataType("*/*");
  
  intentF = new IntentFilter[] { ndefDetected };
  techLists = new string[][] {new string[] {
      typeof(Android.Nfc.Tech.NfcA).FullName,
      typeof(Android.Nfc.Tech.MifareClassic).FullName}
  };
  

• OnPause

  NfcManager manager = (NfcManager)GetSystemService(NfcService);
  manager.DefaultAdapter.DisableForegroundDispatch(this);
  

• OnResume

  NfcManager manager = (NfcManager)GetSystemService(NfcService);
  manager.DefaultAdapter.EnableForegroundDispatch(this,mPendingIntent,intentF,techLists);
  

Unfortunately, the foreground dispatch doesn't work (i.e. it does not pick up the tag).

If I change the call to EnableForegroundDispatch() to

manager.DefaultAdapter.EnableForegroundDispatch(this,mPendingIntent,null,null);

the foreground dispatch work fine. But it picks up all tags and not just MIFARE Classic and I get an intent Action_Tag_Discovered instead of Action_Tech_Discovered.

How to use Action_Tech_Discovered with foreground dispatch system?

Did I miss something?

---

tech_list.xml:

<?xml version="1.0" encoding="utf-8" ?>
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
  <tech-list>
    <tech>android.nfc.tech.NfcA</tech>
    <tech>android.nfc.tech.MifareClassic</tech>
  </tech-list>  
</resources>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="m1card_test.m1card_test" android:versionCode="1" android:versionName="1.0">
  <uses-sdk android:minSdkVersion="16" />
  <application android:label="m1card_test"></application>
  <uses-permission android:name="android.permission.NFC" />
</manifest>

My C# code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Nfc;

namespace m1card_test
{
    [Activity(Label = "m1_read",  Icon = "@drawable/icon", LaunchMode = Android.Content.PM.LaunchMode.SingleTask)]
    [IntentFilter(
    new[] {NfcAdapter.ActionTechDiscovered}, 
    Categories = new[] {Intent.CategoryDefault,})]
    [MetaData("android.nfc.action.TECH_DISCOVERED", Resource = "@xml/tech_list")]

    public class m1_read : Activity
    {
        TextView mTV;
        PendingIntent mPendingIntent;
        IntentFilter ndefDetected;
        IntentFilter[] intentF;
        String[][] techLists;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.m1_read);

            Intent Myintent = new Intent(this, GetType());
            Myintent.AddFlags(ActivityFlags.SingleTop);
            mPendingIntent = PendingIntent.GetActivity(this, 0, Myintent, 0);

            ndefDetected = new IntentFilter(NfcAdapter.ActionTechDiscovered);
            ndefDetected.AddDataType("*/*");

            intentF = new IntentFilter[] { ndefDetected };
            techLists = new string[][] {new string[] {
                typeof(Android.Nfc.Tech.NfcA).FullName,
                typeof(Android.Nfc.Tech.MifareClassic).FullName}
            };

            Button button = FindViewById<Button>(Resource.Id.Back_Button);
            mTV = FindViewById<TextView>(Resource.Id.textview);
            button.Click += delegate
            {
                Intent main_intent = new Intent(this, typeof(MainActivity));
                this.StartActivity(main_intent);
                Finish();
            };

        }
        protected override void OnPause()
        {
            base.OnPause();
            NfcManager manager = (NfcManager)GetSystemService(NfcService);
            manager.DefaultAdapter.DisableForegroundDispatch(this);
        }

        protected override void OnResume()
        {
            base.OnResume();
            NfcManager manager = (NfcManager)GetSystemService(NfcService);
            manager.DefaultAdapter.EnableForegroundDispatch(this, mPendingIntent,intentF,techLists);
        }

        protected override void OnNewIntent(Intent intent)
        {
            base.OnNewIntent(intent);
            mTV.Text = "OnNewIntent";
        }
    }
}

Answer 1

The TECH_DISCOVERED intent filter does not have a data-type (MIME type) associated with it. Thus you need to remove the line

ndefDetected.AddDataType("*/*");

Moreover, I'm not quite sure if typeof(Android.Nfc.Tech.MifareClassic).FullName resolves to the correct name (full Java class name) of the tag technology. Thus, you should probably hard-code that string (just as you do in the tech-filter XML file):

techLists = new string[][] { new string[] {
    "android.nfc.tech.NfcA",
    "android.nfc.tech.MifareClassic"
}};

Finally, since the MifareClassic tag technology always implies NfcA, you can safely reduce the tech-filter to just

techLists = new string[][] { new string[] {
    "android.nfc.tech.MifareClassic"
}};