Android Error: Unable to resume activity..?

Question

I'm new to android and trying to add Facebook login and catch the event after clicking the Logout button(using AccessTokenTracker) in android using facebook sdk using Android studio but i'm getting this error

here is the logcat,

// (please horizontal scroll for logcat)
01-12 00:47:15.306 12572-12572/com.example.arpit.facebooklogindemo E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                 java.lang.RuntimeException: Unable to resume activity {com.example.arpit.facebooklogindemo/com.example.arpit.facebooklogindemo.MainActivity}: java.lang.NullPointerException
 at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2790)
 at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2819)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2266)
 at android.app.ActivityThread.access$600(ActivityThread.java:141)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
 at android.os.Handler.dispatchMessage(Handler.java:99)
 at android.os.Looper.loop(Looper.java:137)
 at android.app.ActivityThread.main(ActivityThread.java:5103)
 at java.lang.reflect.Method.invokeNative(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:525)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
 at dalvik.system.NativeStart.main(Native Method)
                                                                                  Caused by: java.lang.NullPointerException
 at com.example.arpit.facebooklogindemo.MainActivity.onResume(MainActivity.java:83)
 at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
 at android.app.Activity.performResume(Activity.java:5211)
 at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2780)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2819) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2266) 
at android.app.ActivityThread.access$600(ActivityThread.java:141) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:5103) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:525) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
at dalvik.system.NativeStart.main(Native Method)

Here is AndroidManifest.xml,

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.arpit.facebooklogindemo">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

         //from http://developers.facebook.com
        <meta-data android:name="com.facebook.sdk.ApplicationId"
            android:value="@string/app_id"/>

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        //from http://developers.facebook.com
        <activity android:name="com.facebook.FacebookActivity"
            android:configChanges=
                "keyboard|keyboardHidden|screenLayout|screenSize|orientation"
            android:theme="@android:style/Theme.Translucent.NoTitleBar"
            android:label="@string/app_name" />

    </application>

</manifest>

Here is activity_main.xml,

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.arpit.facebooklogindemo.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        android:id="@+id/textView2" />

     //from http://developers.facebook.com
    <com.facebook.login.widget.LoginButton
        android:id="@+id/login_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/textView"
        android:layout_above="@+id/login_button"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="90dp" />

</RelativeLayout>

Here is MainActivity.java,

package com.example.arpit.facebooklogindemo;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;

import com.facebook.AccessToken;
import com.facebook.AccessTokenTracker;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.FacebookSdk;
import com.facebook.Profile;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;

public class MainActivity extends AppCompatActivity {

    CallbackManager callbackManager;
    LoginButton loginButton;
    TextView textView;
    AccessTokenTracker accessTokenTracker;

    private FacebookCallback<LoginResult> mFacebookCallback = new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            Profile profile = Profile.getCurrentProfile();
            if(profile != null){
                fillTextView(profile);
            }
        }

        @Override
        public void onCancel() {

        }

        @Override
        public void onError(FacebookException error) {
            Log.d("find", String.valueOf(error));
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        FacebookSdk.sdkInitialize(getApplicationContext());
        setContentView(R.layout.activity_main);
        textView = (TextView)findViewById(R.id.textView);

        callbackManager = CallbackManager.Factory.create();

        accessTokenTracker = new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(AccessToken oldAccessToken, AccessToken currentAccessToken) {
                if(currentAccessToken == null){
                    textView.setText("Logged out");
                }
            }
        };
        accessTokenTracker.startTracking();

        loginButton = (LoginButton)findViewById(R.id.login_button);

        loginButton.registerCallback(callbackManager, mFacebookCallback);

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        callbackManager.onActivityResult(requestCode, resultCode, data);
    }

    @Override
    protected void onResume(){
        super.onResume();
        Profile profile = Profile.getCurrentProfile();
        textView.setText(profile.getName());
    }

    @Override
    protected void onDestroy(){
        super.onDestroy();
        accessTokenTracker.stopTracking();
    }

    private void fillTextView(Profile profile){
        textView.setText(profile.getName());
    }
}

Solution

Look at this line in your logs:

Caused by: java.lang.NullPointerException
at com.example.arpit.facebooklogindemo.MainActivity.onResume(MainActivity.java:83)

It is clearly mentioned that your app is crashing due to NullPointerException in onResume() function. One possible reason is you might be getting null profile details while calling profile.getName()

Make a null checking before setting text as below:

Profile profile = Profile.getCurrentProfile();
if(null != profile)
        textView.setText(profile.getName());

Sometimes, you might get null or old profile details. In such case, you need to request for updated profile details. Below is samle code:

 Profile profile = Profile.getCurrentProfile();
    if(null != profile) {
          new ProfileTracker() {
                                @Override
                                protected void onCurrentProfileChanged(Profile oldProfile, Profile currentProfile) {
                                    if (currentProfile != null) {
                                        // handle it
                                        stopTracking();
                                    }
                                }
                            }.startTracking();
    } else {
            textView.setText(profile.getName());
}