title: NullPointer Exception While Doing Search Feature for ListView With BaseAdapter
body: <p>I just finished adding a search feature to my android widget to search through a list of the users installed applications. My app installs fine and everything but when I go to search something the app force closes and I get this error:</p>
  
  <pre><code>10-18 11:10:49.393: E/AndroidRuntime(10901): FATAL EXCEPTION: main
  10-18 11:10:49.393: E/AndroidRuntime(10901): java.lang.NullPointerException
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at com.example.awesomefilebuilderwidget.AppInfoAdapter.getCount(AppInfoAdapter.java:33)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.widget.AdapterView$AdapterDataSetObserver.onChanged(AdapterView.java:778)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.database.DataSetObservable.notifyChanged(DataSetObservable.java:31)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.widget.BaseAdapter.notifyDataSetChanged(BaseAdapter.java:50)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at com.example.awesomefilebuilderwidget.AppInfoAdapter$1.publishResults(AppInfoAdapter.java:98)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.widget.Filter$ResultsHandler.handleMessage(Filter.java:282)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.os.Handler.dispatchMessage(Handler.java:99)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.os.Looper.loop(Looper.java:150)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at android.app.ActivityThread.main(ActivityThread.java:4333)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at java.lang.reflect.Method.invokeNative(Native Method)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at java.lang.reflect.Method.invoke(Method.java:507)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
  10-18 11:10:49.393: E/AndroidRuntime(10901):    at dalvik.system.NativeStart.main(Native Method)
  </code></pre>
  
  <p>Here is my AppInfoAdapter so I might have messed up somewhere along the line:</p>
  
  <pre><code>package com.example.awesomefilebuilderwidget;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import android.content.Context;
  import android.content.pm.ApplicationInfo;
  import android.content.pm.PackageManager;
  import android.view.LayoutInflater;
  import android.view.View;
  import android.view.ViewGroup;
  import android.widget.BaseAdapter;
  import android.widget.Filter;
  import android.widget.Filterable;
  import android.widget.ImageView;
  import android.widget.TextView;
  
  public class AppInfoAdapter extends BaseAdapter implements Filterable {
  private Context mContext;
  private List&lt;ApplicationInfo&gt; mListAppInfo;
  private PackageManager mPackManager;
  private List&lt;ApplicationInfo&gt; originalListAppInfo;
  private Filter filter;
  
  public AppInfoAdapter(Context c, List&lt;ApplicationInfo&gt; listApp, PackageManager pm) {
      mContext = c;
      this.originalListAppInfo = this.mListAppInfo = listApp;
      mPackManager = pm;
      }
  
  @Override
  public int getCount() {
      return mListAppInfo.size();
  }
  
  @Override
  public Object getItem(int position) {
      return mListAppInfo.get(position);
  }
  
  @Override
  public long getItemId(int position) {
      return position;
  }
  
  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
      // get the selected entry
      ApplicationInfo entry = (ApplicationInfo) mListAppInfo.get(position);
  
      // reference to convertView
      View v = convertView;
  
      // inflate new layout if null
      if(v == null) {
          LayoutInflater inflater = LayoutInflater.from(mContext);
          v = inflater.inflate(R.layout.layout_appinfo, null);
      }
  
      // load controls from layout resources
      ImageView ivAppIcon = (ImageView)v.findViewById(R.id.ivIcon);
      TextView tvAppName = (TextView)v.findViewById(R.id.tvName);
      TextView tvPkgName = (TextView)v.findViewById(R.id.tvPack);
  
      // set data to display
      ivAppIcon.setImageDrawable(entry.loadIcon(mPackManager));
      tvAppName.setText(entry.loadLabel(mPackManager));
      tvPkgName.setText(entry.packageName);
  
      // return view
      return v;
  }
  @Override
  public Filter getFilter() {
      if(filter == null) {
          filter = new Filter() {
              @Override
              protected FilterResults performFiltering(CharSequence constraint) {
                  FilterResults results = new FilterResults();
                  List&lt;ApplicationInfo&gt; myFilteredAppList = new ArrayList&lt;ApplicationInfo&gt;();
                  constraint = constraint.toString().toLowerCase();
  
                  for (ApplicationInfo appInfo : originalListAppInfo) {
                      String somefield = appInfo.name;
                      if (somefield.toLowerCase().contains(constraint.toString())) {
                          myFilteredAppList.add(appInfo);
                      }
                  }
                  results.count = myFilteredAppList.size();
                  results.values = myFilteredAppList;
                  return results;
              }
  
  
              @Override
              protected void publishResults(CharSequence constraint, FilterResults results) {
                  mListAppInfo = (List&lt;ApplicationInfo&gt;)results.values;
                  notifyDataSetChanged();
              }
          };
      }
      return filter;
  }
  
  }
  </code></pre>
  
  <p>What's the problem? </p>
  
  <p>ADDED: Here is my Drag_and_Drop_App.java:</p>
  
  <pre><code>package com.example.awesomefilebuilderwidget;
  
  import java.util.List;
  
  import android.app.Activity;
  import android.content.Intent;
  import android.content.pm.ApplicationInfo;
  import android.os.Bundle;
  import android.text.Editable;
  import android.text.TextWatcher;
  import android.util.Log;
  import android.view.View;
  import android.widget.AdapterView;
  import android.widget.AdapterView.OnItemClickListener;
  import android.widget.AdapterView.OnItemLongClickListener;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.ListView;
  
  public class Drag_and_Drop_App extends Activity {
  private ListView mListAppInfo;
  // Search EditText
  EditText inputSearch;
  public static AppInfoAdapter adapter;
  
  
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      // set layout for the main screen
      setContentView(R.layout.drag_and_drop_app);
      // import buttons
      Button btnLinkToFeedback = (Button) findViewById(R.id.btnLinkToFeedback);
  
      // Link to Feedback Screen
      btnLinkToFeedback.setOnClickListener(new View.OnClickListener() {
  
          public void onClick(View view) {
              Intent i = new Intent(getApplicationContext(),
                      Feedback.class);
              startActivity(i);
              finish();
          }
      });
      // create new adapter
      adapter = new AppInfoAdapter(this, (List&lt;ApplicationInfo&gt;) Utilities.getInstalledApplication(this), getPackageManager());
      // load list application
     mListAppInfo = (ListView)findViewById(R.id.lvApps);
      // set adapter to list view
      mListAppInfo.setAdapter(adapter);
      // search bar
      inputSearch = (EditText) findViewById(R.id.inputSearch);
  
      inputSearch.addTextChangedListener(new TextWatcher() {
  
          @Override
          public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
              // When user changed the Text
              // Drag_and_Drop_App.this.adapter.getFilter().filter(cs);  
               if (Drag_and_Drop_App.this.adapter == null){
                   // some print statement saying it is null
                   Log.d ("msg_error", "adapter_is_null");
               }
                  Drag_and_Drop_App.this.adapter.getFilter().filter(cs);
  
              }
  
          @Override
          public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
                  int arg3) {
              // TODO Auto-generated method stub
  
          }
  
          @Override
          public void afterTextChanged(Editable arg0) {
              // TODO Auto-generated method stub                          
          }
          });
  
  
      // implement event when an item on list view is selected
      mListAppInfo.setOnItemClickListener(new OnItemClickListener() {
  
          @Override
          public void onItemClick(AdapterView&lt;?&gt; parent, View view, int pos, long id) {
              // get the list adapter
              AppInfoAdapter appInfoAdapter = (AppInfoAdapter)parent.getAdapter();
              // get selected item on the list
              ApplicationInfo appInfo = (ApplicationInfo)appInfoAdapter.getItem(pos);
              // launch the selected application
              Utilities.launchApp(parent.getContext(), getPackageManager(), appInfo.packageName);
          }
  
      });
  
      // implement event when an item on list view is selected via long-click for drag and drop
      mListAppInfo.setOnItemLongClickListener(new OnItemLongClickListener(){
  
          @Override
          public boolean onItemLongClick(AdapterView&lt;?&gt; parent, View view,
                  int pos, long id) {
              // TODO Auto-generated method stub
              // get the list adapter
              AppInfoAdapter appInfoAdapter = (AppInfoAdapter)parent.getAdapter();
              // get selected item on the list
              ApplicationInfo appInfo = (ApplicationInfo)appInfoAdapter.getItem(pos);
              // launch the selected application
              Utilities.launchApp(parent.getContext(), getPackageManager(), appInfo.packageName);
              return true;
          }
  
  
      });
  }
  }
  </code></pre>
  
  <p>ADDED CLASS: Here is my Utilities class:</p>
  
  <pre><code>package com.example.awesomefilebuilderwidget;
  
  import java.util.List;
  
  import android.content.ActivityNotFoundException;
  import android.content.Context;
  import android.content.Intent;
  import android.content.pm.PackageManager;
  import android.widget.Toast;
  
  public class Utilities {
  
  /*
   * Get all installed application on mobile and return a list
   * @param   c   Context of application
   * @return  list of installed applications
   */
  public static List&lt;?&gt; getInstalledApplication(Context c) {
      return c.getPackageManager().getInstalledApplications(PackageManager.GET_META_DATA);
  }
  
  /*
   * Launch an application
   * @param   c   Context of application
   * @param   pm  the related package manager of the context
   * @param   pkgName Name of the package to run
   */
  public static boolean launchApp(Context c, PackageManager pm, String pkgName) {
      // query the intent for lauching
      Intent intent = pm.getLaunchIntentForPackage(pkgName);
      // if intent is available
      if(intent != null) {
          try {
              // launch application
              c.startActivity(intent);
              // if succeed
              return true;
  
          // if fail
          } catch(ActivityNotFoundException ex) {
              // quick message notification
              Toast toast = Toast.makeText(c, "Application Not Found", Toast.LENGTH_LONG);
              // display message
              toast.show();
          }
      }
      // by default, fail to launch
      return false;
  }
  }
  </code></pre>