I want my phone to detect if there is a nfc tag near by (near the surface of it) The following code has no errors but as soon as i run the app, it crashes. It would be very helpful if someone of you can look through my code and check if there is something i dont see. Down bellow is the runtimeerror.
public class AccessControlActivity extends AppCompatActivity {
NfcAdapter nfcAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_access_control);
nfcAdapter = NfcAdapter.getDefaultAdapter(this);
// Checks if there is NFC function
if(nfcAdapter != null && nfcAdapter.isEnabled()) {
//Toast.makeText(this, "NFC works", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(this, "NFC is not available!", Toast.LENGTH_SHORT).show();
//finish();
}
}
@Override
protected void onNewIntent(Intent intent) {
Toast.makeText(this, "NFC intent received", Toast.LENGTH_LONG).show();
super.onNewIntent(intent);
}
@Override
protected void onResume() {
Intent intent = new Intent(this, AccessControlActivity.class);
intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
IntentFilter[] intentFilters = new IntentFilter[]{};
nfcAdapter.enableForegroundDispatch(this, pendingIntent, intentFilters, null);
super.onResume();
}
@Override
protected void onPause() {
nfcAdapter.disableForegroundDispatch(this);
super.onPause();
}
}
The runtimeerror looks like this:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.nfc.netvision, PID: 5484
java.lang.RuntimeException: Unable to resume activity {com.nfc.netvision/com.nfc.netvision.AccessControlActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.nfc.NfcAdapter.enableForegroundDispatch(android.app.Activity, android.app.PendingIntent, android.content.IntentFilter[], java.lang.String[][])' on a null object reference
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:4341)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:4373)
at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:52)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2043)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:216)
at android.app.ActivityThread.main(ActivityThread.java:7464)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:955)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.nfc.NfcAdapter.enableForegroundDispatch(android.app.Activity, android.app.PendingIntent, android.content.IntentFilter[], java.lang.String[][])' on a null object reference
at com.nfc.netvision.AccessControlActivity.onResume(AccessControlActivity.java:116)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1456)
at android.app.Activity.performResume(Activity.java:8125)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:4331)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:4373)
at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:52)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2043)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:216)
at android.app.ActivityThread.main(ActivityThread.java:7464)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:955)
I/Process: Sending signal. PID: 5484 SIG: 9
So you check that the nfcAdapter != null in onCreate and just show a toast, your app will then blindly go and try and use a possibly null adapter in onResume.
This would explain the Attempt to invoke virtual method on a null object reference in onResume as the variable nfcAdapter is probably null in onResume
You should check for null again in onResume
Also your Intent filters don't look right as well, they code either cause no Intents to be sent to you or the opposite cause all including non NFC Intents to be sent to you.
More normal code to get called when any type of tag is presented would be.
@Override
protected void onResume() {
super.onResume();
IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
IntentFilter ndefDetected = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED);
try {
ndefDetected.addDataType("*/*");
} catch (IntentFilter.MalformedMimeTypeException e) {}
IntentFilter techDetected = new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED);
IntentFilter[] nfcIntentFilter = new IntentFilter[]{ndefDetected,techDetected,tagDetected};
PendingIntent pendingIntent = PendingIntent.getActivity(
this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
if(nfcAdapter!= null)
nfcAdapter.enableForegroundDispatch(this, pendingIntent, nfcIntentFilter, null);
}
@Override
protected void onPause() {
super.onPause();
if(nfcAdapter!= null)
nfcAdapter.disableForegroundDispatch(this);
}