Android: Null Pointer Exception when calling new i

I am receiving an error when trying to call new activity through an intent:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference

My Activity has a button, and when clicked, it goes to this method:

public void onClickChangeActivity() {

        Intent intent = new Intent(context , Details.class);
        startActivity(intent);

    }

public static Context context is created in the beginning of the class and then is instantiated in my onCreate as context = getApplicationContext();

I've also tried context = getBaseContext() and context = RecyclerViewActivity.this (RecyclerViewActivity is the name of my current class)

Any help as to why I'm receiving this NullP? I've tried everything related StackOverFlow answers have offered. Also, my Manifest includes my activity.

onClickChangeActivity is being called from my RecyclerViewerAdapter class:

View.OnClickListener getPersonClickListener(final int position) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View view) {


                RecyclerViewActivity recyclerViewActivity = new RecyclerViewActivity();
                recyclerViewActivity.onClickChangeActivity();
            }
        };

Manifest File:

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

    <uses-sdk
        android:minSdkVersion="16"
        android:targetSdkVersion="21" />

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission
        android:name="android.permission.WRITE_EXTERNAL_STORAGE"
        android:maxSdkVersion="18" />
    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission
        android:name="android.permission.READ_EXTERNAL_STORAGE"
        android:maxSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <!-- <activity -->
        <!-- android:name=".DataFetcher" -->
        <!-- android:label="@string/title_activity_data_fetcher" > -->
        <!-- </activity> -->
        <activity
            android:name=".Crime"
            android:label="@string/title_activity_crime"
            android:screenOrientation="portrait" >
        </activity>
        <activity
            android:name=".RecyclerViewActivity"
            android:label="@string/title_activity_recycler_view"
            android:screenOrientation="portrait" >
        </activity>
        <activity
            android:name=".Details"
            android:label="@string/title_activity_crime_details"
            android:parentActivityName=".RecyclerViewActivity" >
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value="RecyclerViewActivity" />
        </activity>
    </application>

</manifest>

LogCat:

 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
            at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
            at android.content.ComponentName.<init>(ComponentName.java:77)
            at android.content.Intent.<init>(Intent.java:4160)
            at com.bah.baltimoreopendata.android_baltimoreopendata.RecyclerViewActivity.onClickChangeActivity(RecyclerViewActivity.java:265)
            at com.bah.baltimoreopendata.android_baltimoreopendata.RecycleViewAdapter$1.onClick(RecycleViewAdapter.java:121)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

回答1:

Problem is that you are trying to call an activity method from the adapter:

RecyclerViewActivity recyclerViewActivity = new RecyclerViewActivity();
recyclerViewActivity.onClickChangeActivity();

You should replace this code in adapter class. In the adapter constructor add the following lines:

public RecycleViewAdapter(......, Context context){
    ...your code.
    this.mContext=context;
}

And in In the getPersonClickListener adapter method:

View.OnClickListener getPersonClickListener(final int position) {
    return new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(mContext instanceof RecyclerViewActivity){
                ((RecyclerViewActivity)mContext).onClickChangeActivity();
            }
        }
    };

And when you invoke onClickChangeActivity method on RecyclerViewActivity use:

public void onClickChangeActivity() {
    Intent intent = new Intent(RecyclerViewActivity.this, Details.class);
    startActivity(intent);
}

And be sure that Details.class extends Activity.

回答2:

try this:

Intent intent = new Intent(RecyclerViewActivity.this , Details.class);
startActivity(intent);

use RecyclerViewActivity.this instead of context

回答3:

Solution:

In the adapter class create a private static Context context;

In your inCreateViewHolder(), instantiate context to viewGroup.getContext():

@Override
    public PersonViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item, viewGroup, false);
        PersonViewHolder pvh = new PersonViewHolder(v);
        context = viewGroup.getContext();
        return pvh;
    }

This is the reason I was getting a Null Pointer Exception. For some reason, what I create a constructor with a context, context was still null. Instantiating context in the above class did the trick! Thanks to all who answered.

回答4:

You are trying to start Details.class -

But I can not find any references to this activity in your manifest.

Please add

<activity android:name=".Details"</activity>

To your manifest and make sure that Details extends Activity.