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Attempt to call void virtual method android.widget.ListView.setAdapter

I am trying to create a list view that contains images and text inside a fragment that is in a tabbed view pane, so I can scroll left or right to bring up another fragment.

I am relatively new to android, so what I can do may be completely wrong. I can build the project perfectly, but then when the emulator starts to crash it (the log is displayed at the bottom of the page).

I created a separate application and was able to successfully create a list view, but when I try to combine it inside a fragment, it does not work. Here is my next code

MainActivity.java

import java.util.ArrayList; import java.util.List; import java.util.Locale; import android.app.ListFragment; import android.content.Intent; import android.support.v7.app.ActionBarActivity; import android.support.v7.app.ActionBar; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentTransaction; import android.support.v4.app.FragmentPagerAdapter; import android.os.Bundle; import android.support.v4.view.ViewPager; import android.view.Gravity; import android.view.LayoutInflater; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.view.ViewGroup; import android.widget.AdapterView; import android.widget.ArrayAdapter; import android.widget.ImageView; import android.widget.ListView; import android.widget.TextView; import android.widget.Toast; public class MainActivity extends ActionBarActivity implements ActionBar.TabListener { /** * The {@link android.support.v4.view.PagerAdapter} that will provide * fragments for each of the sections. We use a * {@link FragmentPagerAdapter} derivative, which will keep every * loaded fragment in memory. If this becomes too memory intensive, it * may be best to switch to a * {@link android.support.v4.app.FragmentStatePagerAdapter}. */ SectionsPagerAdapter mSectionsPagerAdapter; /** * The {@link ViewPager} that will host the section contents. */ ViewPager mViewPager; private List<Posts> myPosts = new ArrayList<Posts>(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // Set up the action bar. final ActionBar actionBar = getSupportActionBar(); actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); // Create the adapter that will return a fragment for each of the three // primary sections of the activity. mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); // Set up the ViewPager with the sections adapter. mViewPager = (ViewPager) findViewById(R.id.pager); mViewPager.setAdapter(mSectionsPagerAdapter); // When swiping between different sections, select the corresponding // tab. We can also use ActionBar.Tab#select() to do this if we have // a reference to the Tab. mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() { @Override public void onPageSelected(int position) { actionBar.setSelectedNavigationItem(position); } }); // For each of the sections in the app, add a tab to the action bar. for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) { // Create a tab with text corresponding to the page title defined by // the adapter. Also specify this Activity object, which implements // the TabListener interface, as the callback (listener) for when // this tab is selected. actionBar.addTab( actionBar.newTab() .setText(mSectionsPagerAdapter.getPageTitle(i)) .setTabListener(this)); } Intent intent = new Intent(MainActivity.this, NotMainActivity.class); startActivity(intent); finish(); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); //noinspection SimplifiableIfStatement if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } @Override public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { // When the given tab is selected, switch to the corresponding page in // the ViewPager. mViewPager.setCurrentItem(tab.getPosition()); } @Override public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { } @Override public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { } /** * A {@link FragmentPagerAdapter} that returns a fragment corresponding to * one of the sections/tabs/pages. */ public class SectionsPagerAdapter extends FragmentPagerAdapter { public SectionsPagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int position) { // getItem is called to instantiate the fragment for the given page. // Return a PlaceholderFragment (defined as a static inner class below). switch (position){ case 0: return new TheWallFragment(); case 1: return new PeekFragment(); case 2: return new CameraFragment(); default: break; } return PlaceholderFragment.newInstance(position + 1); } @Override public int getCount() { // Show 3 total pages. return 3; } @Override public CharSequence getPageTitle(int position) { Locale l = Locale.getDefault(); switch (position) { case 0: return getString(R.string.title_section1).toUpperCase(l); case 1: return getString(R.string.title_section2).toUpperCase(l); case 2: return getString(R.string.title_section3).toUpperCase(l); } return null; } } /** * A placeholder fragment containing a simple view. */ public static class PlaceholderFragment extends Fragment { /** * The fragment argument representing the section number for this * fragment. */ private static final String ARG_SECTION_NUMBER = "section_number"; /** * Returns a new instance of this fragment for the given section * number. */ public static PlaceholderFragment newInstance(int sectionNumber) { PlaceholderFragment fragment = new PlaceholderFragment(); Bundle args = new Bundle(); args.putInt(ARG_SECTION_NUMBER, sectionNumber); fragment.setArguments(args); return fragment; } public PlaceholderFragment() { } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.wall_layout, container, false); return rootView; } } }

NotMainActivity.java

 public class NotMainActivity extends FragmentActivity { private List<Posts> myPosts = new ArrayList<Posts>(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); populatePostList(); populateListView(); registerClickCallBack(); System.out.print("Main Activity Started"); } private void populatePostList() { myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); myPosts.add(new Posts("Ottawa, Ontario", "787", "Picture of my Dog!", R.drawable.dog)); } private void populateListView() { ArrayAdapter<Posts> adapter = new MyListAdapter(); ListView list = (ListView) findViewById(android.R.id.list); list.setAdapter(adapter); } //Handles clicks on the list items private void registerClickCallBack(){ ListView list = (ListView) findViewById(android.R.id.list); list.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { Posts clickedPost = myPosts.get(position); String message = "You clicked" + position +"Location of post is" + clickedPost.getPostlocation(); Toast.makeText(NotMainActivity.this, message, Toast.LENGTH_LONG).show(); } }); } private class MyListAdapter extends ArrayAdapter<Posts> { public MyListAdapter() { super(NotMainActivity.this, R.layout.item_view, myPosts); } @Override public View getView(int position, View convertView, ViewGroup parent) { // Make sure we have a view to work with {may have given null} View itemView = convertView; if (itemView != null) { itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false); } // Find the post to work with. Posts currentPost = myPosts.get(position); //Fill the view ImageView imageView = (ImageView)itemView.findViewById(R.id.item_postImage); imageView.setImageResource(currentPost.getIconID()); //Fill in Title TextView titleText = (TextView) itemView.findViewById(R.id.item_postText); titleText.setText(currentPost.getPosttitle()); //Set Vote Number TextView voteText = (TextView) itemView.findViewById(R.id.item_postVoteText); voteText.setText(currentPost.getPostvote()); return itemView; } } }

Posts.java

 public class Posts { private String postlocation; private String postvote; private String posttitle; private int iconID; public Posts(String postlocation, String postvote, String posttitle, int iconID) { this.postlocation = postlocation; this.postvote = postvote; this.posttitle = posttitle; this.iconID = iconID; } public String getPostlocation() { return postlocation; } public String getPostvote() { return postvote; } public String getPosttitle() { return posttitle; } public int getIconID() { return iconID; }

TheWallFragment.java

 public class TheWallFragment extends android.support.v4.app.ListFragment { List<Posts> myPosts = new ArrayList<Posts>(); private String[] strListView; private ListView myListView; private int number; public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.wall_layout, container, false); return rootView; } }

activity_main.xml

 <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity" />

AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.gnumbu.errolgreen.testing" > <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" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".NotMainActivity"> </activity> </application> </manifest>

item_view.xml

  <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/item_postImage" android:src="@drawable/dog" android:maxWidth="80dp" android:minHeight="80dp" android:adjustViewBounds="true" android:layout_marginLeft="14dp" android:layout_marginStart="14dp" android:layout_alignParentTop="true" android:layout_toRightOf="@+id/item_upvoteArrow" android:layout_toEndOf="@+id/item_upvoteArrow" android:layout_alignBottom="@+id/item_downvotearrow" /> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="This is my dog! My Dog is amazing, give it a lick!" android:id="@+id/item_postText" android:paddingStart="5dp" android:layout_above="@+id/item_downvotearrow" android:layout_toRightOf="@+id/item_postImage" android:layout_toEndOf="@+id/item_postImage" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/item_upvoteArrow" android:src="@drawable/upvotearrow" android:maxHeight="24dp" android:maxWidth="24dp" android:adjustViewBounds="true" android:layout_alignParentTop="true" android:layout_alignLeft="@+id/item_downvotearrow" android:layout_alignStart="@+id/item_downvotearrow" android:clickable="true" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/item_downvotearrow" android:src="@drawable/downvotearrow" android:maxWidth="24dp" android:maxHeight="24dp" android:adjustViewBounds="true" android:layout_marginLeft="9dp" android:layout_marginStart="9dp" android:layout_below="@+id/item_postVoteText" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:longClickable="false" android:clickable="true" /> <TextView android:layout_height="wrap_content" android:text="22" android:id="@+id/item_postVoteText" android:maxHeight="20dp" android:focusableInTouchMode="false" android:visibility="visible" android:singleLine="true" android:gravity="center" android:enabled="true" android:layout_below="@+id/item_upvoteArrow" android:layout_alignLeft="@+id/item_upvoteArrow" android:layout_alignStart="@+id/item_upvoteArrow" android:nestedScrollingEnabled="false" android:layout_width="wrap_content" android:layout_toStartOf="@+id/item_postImage" /> </RelativeLayout>

wall_layout.xml

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="New Text" android:id="@+id/textView" android:layout_gravity="center_horizontal" /> <ListView android:id="@android:id/list" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout>

Error log

  java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5223) 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:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at com.gnumbu.errolgreen.testing.NotMainActivity.populateListView(NotMainActivity.java:70) at com.gnumbu.errolgreen.testing.NotMainActivity.onCreate(NotMainActivity.java:43) at android.app.Activity.performCreate(Activity.java:5937) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)            at android.app.ActivityThread.access$800(ActivityThread.java:144)            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)            at android.os.Handler.dispatchMessage(Handler.java:102)            at android.os.Looper.loop(Looper.java:135)            at android.app.ActivityThread.main(ActivityThread.java:5223)            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:899)            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

New mistake

  Process: com.gnumbu.errolgreen.testing, PID: 5304 java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getImportantForAccessibility()' on a null object reference at android.widget.AbsListView.obtainView(AbsListView.java:2360) at android.widget.ListView.measureHeightOfChildren(ListView.java:1270) at android.widget.ListView.onMeasure(ListView.java:1182) at android.view.View.measure(View.java:17430) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) at android.view.View.measure(View.java:17430) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) at android.widget.FrameLayout.onMeasure(FrameLayout.java:430) at android.view.View.measure(View.java:17430) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) at android.view.View.measure(View.java:17430) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) at android.widget.FrameLayout.onMeasure(FrameLayout.java:430) at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560) at android.view.View.measure(View.java:17430) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) at android.view.Choreographer.doCallbacks(Choreographer.java:580) at android.view.Choreographer.doFrame(Choreographer.java:550) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) 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:5221) 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:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
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2 answers

NotMainActivity calls setContentView with R.layout.activity_main as a parameter containing a ViewPager , not a ListView . Since you do not have a ListView declaration in this layout, findViewById(android.R.id.list) returns null, and when you try to access it (call setAdapter ), a NullPointerException is NullPointerException .

in MyAdapter , change

 if (itemView != null) { itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false); }

to

 if (itemView == null) { itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false); }
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Here is what I could get:

 indexBar = (ProgressBar) findViewById(R.id.mainIndexProgressBar); Drawable d = ContextCompat.getDrawable(getApplicationContext(), R.drawable.ic_check_circle_black_24dp); d.setBounds(0, 0, indexBar.getWidth(), indexBar.getHeight()); indexBar.setIndeterminateDrawable(d); indexBar.setIndeterminate(true); indexBar.requestLayout();
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Source: https://habr.com/ru/post/1216635/

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