How to fix Android app crashing that uses Firebase?

Question

My problem is quite a troublesome one, i made an app on Android Studio that has a TextView that displays the Firebase registration token upon launch (I'm still new to Firebase and Android Studio, i'm experimenting), i've been building APK files of my app to test it on my phone since Android Studio doesn't detect my phone when it's hooked to my laptop for some reason and i can't use emulation because my laptop is old (i think it doesn't support virtualization), so whenever i try to launch my app on my phone i get the equivalent of MyApp stopped working in French and i don't know how to view the crash log files.

tl;dr i wanna know what's causing my app to crash

MainActivity.java

package com.gci.gestioncapteursincendie;

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.widget.TextView;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.iid.FirebaseInstanceId;
import com.google.firebase.iid.InstanceIdResult;

public class MainActivity extends AppCompatActivity {

    private TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView= findViewById(R.id.textViewToken);
        FirebaseInstanceId.getInstance().getInstanceId()
                .addOnCompleteListener(new OnCompleteListener<InstanceIdResult>() {
                    @Override
                    public void onComplete(@NonNull Task<InstanceIdResult> task) {
                      if(task.isSuccessful()){
                          String token = task.getResult().getToken();
                          textView.setText("Token : " + token);
                        }
                        else
                      {
                          textView.setText("Token Not Generated");
                      }
                    }
                });
    }

}

Edit: i managed to run my app on my phone through Android Studio by downloading the right drivers, i checked the logcat when i ran it and i got this:

03-31 18:55:45.069 8855-8855/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.gci.gestioncapteursincendie, PID: 8855
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gci.gestioncapteursincendie/com.gci.gestioncapteursincendie.MainActivity}: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.gci.gestioncapteursincendie. Make sure to call FirebaseApp.initializeApp(Context) first.
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
        at android.app.ActivityThread.access$1100(ActivityThread.java:229)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:7406)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
     Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.gci.gestioncapteursincendie. Make sure to call FirebaseApp.initializeApp(Context) first.
        at com.google.firebase.FirebaseApp.getInstance(com.google.firebase:firebase-common@@16.0.1:219)
        at com.google.firebase.iid.FirebaseInstanceId.getInstance(Unknown Source)
        at com.gci.gestioncapteursincendie.MainActivity.onCreate(MainActivity.java:38)
        at android.app.Activity.performCreate(Activity.java:6904)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7406) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 

Edit 2: I added the following line of code referred by user Riley Manda:

FirebaseApp.initializeApp(this);

in onCreate() method and i get this error now:

log trace:

03-31 19:10:19.203 11562-11562/com.gci.gestioncapteursincendie E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.gci.gestioncapteursincendie, PID: 11562
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gci.gestioncapteursincendie/com.gci.gestioncapteursincendie.MainActivity}: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.gci.gestioncapteursincendie. Make sure to call FirebaseApp.initializeApp(Context) first.
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
        at android.app.ActivityThread.access$1100(ActivityThread.java:229)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:7406)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
     Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.gci.gestioncapteursincendie. Make sure to call FirebaseApp.initializeApp(Context) first.
        at com.google.firebase.FirebaseApp.getInstance(com.google.firebase:firebase-common@@16.0.1:219)
        at com.google.firebase.iid.FirebaseInstanceId.getInstance(Unknown Source)
        at com.gci.gestioncapteursincendie.MainActivity.onCreate(MainActivity.java:41)
        at android.app.Activity.performCreate(Activity.java:6904)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7406) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 

Edit 3: I'm making another thread about this problem since it seems like the thread has drifted away from its original purpose, thanks everyone for answering.

Answer 1

Add this FirebaseApp.initializeApp(this);just after setContentView(R.layout.yourlayout); or before you make any connections to firebase

Also for your device not showing in android studio

• first enable developers Options On your Phone https://www.digitaltrends.com/mobile/how-to-get-developer-options-on-android/
• Enable Usb Debugging in the developers Options of your Phone settings
• Secondly install an adb driver on your System and try reconnecting your device
• Accept the prompt on your phone that asks if you want to trust your system and it should work

Answer 2

Connect your app to Crashlytics,this way you will receive crash emails that will lead you to the exact issue thats causing your app to crash.

Follow the instructions on firebase to setup crashlytics for your app in Android Studio.And each time your app crashes, you will receive an email from Crashlytics:

This way, each time your app crashes from your physical devices notification email from Crashlytics is automatically sent to your email indicating the exact line of code/issue that's causing your app to crash.

Based on your crashLog:

You have to initialise firebase in your activity: Add this to your activity:

 FirebaseApp.initializeApp(this);

In your onCreate:

   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.yourlayout);
        FirebaseApp.initializeApp(this);