環境

Android Studio 3.1.2
Java8
実機: Android7

やりたいこと

Twitterに投稿するAndroidアプリを作りたいです。
以下のサイトを参考にしています。

問題

Androidで動かしたら、アプリが終了しました。
LogCatは以下の通りです。

txt
105-19 19:26:44.756 20383-20383/com.example.myapplication4 W/System: ClassLoader referenced unknown path: /data/app/com.example.myapplication4-1/lib/arm64
205-19 19:26:44.783 20383-20383/com.example.myapplication4 I/InstantRun: starting instant run server: is main process
305-19 19:26:44.811 20383-20383/com.example.myapplication4 I/HwCust: Constructor found for class android.app.HwCustActivityImpl
405-19 19:26:44.862 20383-20383/com.example.myapplication4 W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
505-19 19:26:44.964 20383-20383/com.example.myapplication4 E/AndroidRuntime: FATAL EXCEPTION: main
6    Process: com.example.myapplication4, PID: 20383
7    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication4/com.example.myapplication4.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.twitter.sdk.android.core.identity.TwitterLoginButton.setCallback(com.twitter.sdk.android.core.Callback)' on a null object reference
8        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2796)
9        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2867)
10        at android.app.ActivityThread.-wrap12(ActivityThread.java)
11        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1570)
12        at android.os.Handler.dispatchMessage(Handler.java:105)
13        at android.os.Looper.loop(Looper.java:156)
14        at android.app.ActivityThread.main(ActivityThread.java:6595)
15        at java.lang.reflect.Method.invoke(Native Method)
16        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
17        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
18     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.twitter.sdk.android.core.identity.TwitterLoginButton.setCallback(com.twitter.sdk.android.core.Callback)' on a null object reference
19        at com.example.myapplication4.MainActivity.onCreate(MainActivity.java:47)
20        at android.app.Activity.performCreate(Activity.java:6910)
21        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
22        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2749)
23        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2867) 
24        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
25        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1570) 
26        at android.os.Handler.dispatchMessage(Handler.java:105) 
27        at android.os.Looper.loop(Looper.java:156) 
28        at android.app.ActivityThread.main(ActivityThread.java:6595) 
29        at java.lang.reflect.Method.invoke(Native Method) 
30        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942) 
31        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832) 
3205-19 19:26:44.971 20383-20383/com.example.myapplication4 I/Process: Sending signal. PID: 20383 SIG: 9
33

https://github.com/twitter/twitter-kit-android/wiki/Upgrade-to-Twitter-Kit-3.0

質問

エラーの原因を教えていただきたいです。

ソース

MainActivity.java

java
1package com.example.myapplication4;
2
3import android.content.Intent;
4import android.os.Bundle;
5import android.support.v7.app.AppCompatActivity;
6import android.util.Log;
7
8import com.twitter.sdk.android.core.Callback;
9import com.twitter.sdk.android.core.DefaultLogger;
10import com.twitter.sdk.android.core.Result;
11import com.twitter.sdk.android.core.Twitter;
12import com.twitter.sdk.android.core.TwitterAuthConfig;
13import com.twitter.sdk.android.core.TwitterConfig;
14import com.twitter.sdk.android.core.TwitterException;
15import com.twitter.sdk.android.core.TwitterSession;
16import com.twitter.sdk.android.core.identity.TwitterLoginButton;
17
18public class MainActivity extends AppCompatActivity {
19	//add
20
21    TwitterLoginButton loginButton;
22
23    @Override
24    protected void onCreate(Bundle savedInstanceState) {
25        super.onCreate(savedInstanceState);
26
27
28        TwitterConfig config = new TwitterConfig.Builder(this)
29                .logger(new DefaultLogger(Log.DEBUG))
30                .twitterAuthConfig(new TwitterAuthConfig("currentKey", "currentSecret"))
31                .debug(true)
32                .build();
33        Twitter.initialize(config);
34
35
36        loginButton = (TwitterLoginButton) findViewById(R.id.login_button);
37        loginButton.setCallback(new Callback<TwitterSession>() {
38            @Override
39            public void success(Result<TwitterSession> result) {
40                // Do something with result, which provides a TwitterSession for making API calls
41            }
42
43            @Override
44            public void failure(TwitterException exception) {
45                // Do something on failure
46            }
47        });
48
49
50        setContentView(R.layout.activity_main);
51    }
52
53    @Override
54    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
55        super.onActivityResult(requestCode, resultCode, data);
56
57        // Pass the activity result to the login button.
58        loginButton.onActivityResult(requestCode, resultCode, data);
59    }
60}
61

AndroidManifest.xml

xml
1<?xml version="1.0" encoding="utf-8"?>
2<manifest xmlns:android="http://schemas.android.com/apk/res/android"
3          package="com.example.myapplication4">
4
5    <application
6        android:allowBackup="true"
7        android:icon="@mipmap/ic_launcher"
8        android:label="@string/app_name"
9        android:roundIcon="@mipmap/ic_launcher_round"
10        android:supportsRtl="true"
11        android:theme="@style/AppTheme">
12        <activity android:name=".MainActivity">
13            <intent-filter>
14                <action android:name="android.intent.action.MAIN"/>
15
16                <category android:name="android.intent.category.LAUNCHER"/>
17            </intent-filter>
18        </activity>
19    </application>
20
21    <uses-permission android:name="android.permission.INTERNET" />
22</manifest>

Moduleのbuild.gradele

gradle
1buildscript {
2    repositories {
3        maven { url 'https://maven.fabric.io/public' }
4    }
5
6    dependencies {
7        classpath 'io.fabric.tools:gradle:1.+'
8    }
9}
10apply plugin: 'com.android.application'
11apply plugin: 'io.fabric'
12
13repositories {
14    maven { url 'https://maven.fabric.io/public' }
15}
16
17
18android {
19    compileOptions {
20        sourceCompatibility 1.8
21        targetCompatibility 1.8
22    }
23    compileSdkVersion 26
24    defaultConfig {
25        applicationId "com.example.myapplication4"
26        minSdkVersion 24
27        targetSdkVersion 26
28        versionCode 1
29        versionName "1.0"
30        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
31    }
32    buildTypes {
33        release {
34            minifyEnabled false
35            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
36        }
37    }
38    productFlavors {
39    }
40}
41
42repositories {
43    jcenter()
44}
45
46
47dependencies {
48    implementation('com.twitter.sdk.android:twitter:3.3.0@aar') {
49        transitive = true
50    }
51
52    implementation fileTree(include: ['*.jar'], dir: 'libs')
53    implementation 'com.android.support:appcompat-v7:26.1.0'
54    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
55    testImplementation 'junit:junit:4.12'
56    androidTestImplementation 'com.android.support.test:runner:1.0.2'
57    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
58    implementation('com.crashlytics.sdk.android:crashlytics:2.9.2@aar') {
59        transitive = true;
60    }
61}
62

projectのbuild.gradle

gradle
1// Top-level build file where you can add configuration options common to all sub-projects/modules.
2
3buildscript {
4    
5    repositories {
6        google()
7        jcenter()
8    }
9    dependencies {
10        classpath 'com.android.tools.build:gradle:3.1.2'
11        
12
13        // NOTE: Do not place your application dependencies here; they belong
14        // in the individual module build.gradle files
15    }
16}
17
18allprojects {
19    repositories {
20        google()
21        jcenter()
22    }
23}
24
25task clean(type: Delete) {
26    delete rootProject.buildDir
27}
28