Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Android Animations and Transitions Animations Basics Property Animation

Victor Cuc
Victor Cuc
7,281 Points
Posted by Victor Cuc
Victor Cuc
7,281 Points

NullPointerException for setLayoutManager, even if I updated build.gradle dependencies

I updated all the dependencies and it does't seem to be working. Changed @Bind to @BindView, but apparently there still are problems.

Really don't understand why there is a null object. Isn't lm initialised as a new StaggeredGridLayoutManager just at the beginning at the populate() method?

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
                      at com.teamtreehouse.albumcover.AlbumListActivity.populate(AlbumListActivity.java:59)
                      at com.teamtreehouse.albumcover.AlbumListActivity.onCreate(AlbumListActivity.java:27)

private void populate() {
        StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
        mAlbumList.setLayoutManager(lm);

This is the complete exception:

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.jimulabs.googlemusicmock, PID: 4432
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jimulabs.googlemusicmock/com.teamtreehouse.albumcover.AlbumListActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
                      at android.app.ActivityThread.-wrap11(Unknown Source:0)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
                      at android.os.Handler.dispatchMessage(Handler.java:106)
                      at android.os.Looper.loop(Looper.java:164)
                      at android.app.ActivityThread.main(ActivityThread.java:6494)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
                      at com.teamtreehouse.albumcover.AlbumListActivity.populate(AlbumListActivity.java:59)
                      at com.teamtreehouse.albumcover.AlbumListActivity.onCreate(AlbumListActivity.java:27)
                      at android.app.Activity.performCreate(Activity.java:6999)
                      at android.app.Activity.performCreate(Activity.java:6990)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
                      at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
                      at android.os.Handler.dispatchMessage(Handler.java:106) 
                      at android.os.Looper.loop(Looper.java:164) 
                      at android.app.ActivityThread.main(ActivityThread.java:6494) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 

AlbumListActivity:

public class AlbumListActivity extends Activity {

    @BindView(R.id.album_list) RecyclerView mAlbumList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_album_list);
        initTransitions();

        ButterKnife.bind(this);
        populate();
    }

    private void initTransitions() {
        getWindow().setExitTransition(null);
        getWindow().setReenterTransition(null);
    }

    interface OnVHClickedListener {
        void onVHClicked(AlbumVH vh);
    }

    static class AlbumVH extends RecyclerView.ViewHolder implements View.OnClickListener {
        private final OnVHClickedListener mListener;
        @BindView(R.id.album_art)
        ImageView albumArt;

        public AlbumVH(View itemView, OnVHClickedListener listener) {
            super(itemView);
            ButterKnife.bind(this, itemView);
            itemView.setOnClickListener(this);
            mListener = listener;
        }

        @Override
        public void onClick(View v) {
            mListener.onVHClicked(this);
        }
    }

    private void populate() {
        StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
        mAlbumList.setLayoutManager(lm);

        final int[] albumArts = {
                R.drawable.mean_something_kinder_than_wolves,
                R.drawable.cylinders_chris_zabriskie,
                R.drawable.broken_distance_sutro,
                R.drawable.playing_with_scratches_ruckus_roboticus,
                R.drawable.keep_it_together_guster,
                R.drawable.the_carpenter_avett_brothers,
                R.drawable.please_sondre_lerche,
                R.drawable.direct_to_video_chris_zabriskie };

        RecyclerView.Adapter adapter = new RecyclerView.Adapter<AlbumVH>() {
            @Override
            public AlbumVH onCreateViewHolder(ViewGroup parent, int viewType) {
                View albumView = getLayoutInflater().inflate(R.layout.album_grid_item, parent, false);
                return new AlbumVH(albumView, new OnVHClickedListener() {
                    @Override
                    public void onVHClicked(AlbumVH vh) {
                        int albumArtResId = albumArts[vh.getLayoutPosition() % albumArts.length];
                        Intent intent = new Intent(AlbumListActivity.this, AlbumDetailActivity.class);
                        intent.putExtra(AlbumDetailActivity.EXTRA_ALBUM_ART_RESID, albumArtResId);

                        startActivity(intent);
                    }
                });
            }

            @Override
            public void onBindViewHolder(AlbumVH holder, int position) {
                holder.albumArt.setImageResource(albumArts[position % albumArts.length]);
            }

            @Override
            public int getItemCount() {
                return albumArts.length * 4;
            }

        };
        mAlbumList.setAdapter(adapter);
    }

}

build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 27
    buildToolsVersion '26.0.2'

    defaultConfig {
        applicationId "com.jimulabs.googlemusicmock"
        minSdkVersion 21
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    lintOptions {
        disable 'InvalidPackage'
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:recyclerview-v7:27.1.0'
    compile 'com.jakewharton:butterknife:8.8.1'
    annotationProcessor 'com.jakewharton:butterknife:8.8.1'
    compile 'com.jimulabs.mirrorsandbox:mirror-sandbox:0.2.1'
    compile 'com.android.support:palette-v7:27.1.0'
}
Victor Cuc
Victor Cuc
7,281 Points
Victor Cuc
Victor Cuc
7,281 Points

I think I should initialise mAlbumList as that is null, but how should I do that exactly?

Victor Cuc
Victor Cuc
7,281 Points
Victor Cuc
Victor Cuc
7,281 Points

Ben Jakuben is there a problem with how I am using butterknife? I barely changed the starter files...

2 Answers

Victor Cuc
Victor Cuc
7,281 Points
Victor Cuc
Victor Cuc
7,281 Points

FINALLY figured it out!

If anyone else is having this issue, and probably is, you now need to also add the annotationProcessor with butterknife-compiler!

Add this:

dependencies {
  implementation 'com.jakewharton:butterknife:8.8.1' //8.8.1 is the latest version atm
  annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
}

Most importantly, check the README on the ButterKnife Github page! It is the most up to date and tells you exactly how to implement the latest version.

https://github.com/JakeWharton/butterknife

Btw I love how this whole post I've been talking to myself

Nataly Rifold
Nataly Rifold
12,432 Points
Nataly Rifold
Nataly Rifold
12,432 Points

Hi Victor Cuc Thank you!! It works now!!! or I hope it does

the build app gradle file

apply plugin: 'com.android.application'

android {
    compileSdkVersion 27

    defaultConfig {
        applicationId "com.jimulabs.googlemusicmock"
        minSdkVersion 21
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    lintOptions {
        disable 'InvalidPackage'
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:recyclerview-v7:27.1.1'
    implementation 'com.jakewharton:butterknife:7.0.1'
    implementation 'com.jimulabs.mirrorsandbox:mirror-sandbox:0.2.1'
    implementation 'com.android.support:palette-v7:27.1.1'
    implementation 'com.jakewharton:butterknife:8.8.1' //8.8.1 is the latest version atm
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
}

the build modle gradle file

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
        google()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.3.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
        google()
    }
}