Android ListView Null Pointer exception

Question

I've been struggling with populating a ListView in android for a while. Can someone please give me a hand here?

So, I have saved data in a database in 2 different tables. One for settings and one for data to be displayed in a listView. But after watching quite a bunch of tutorials I keep having trouble with populating the list. I am giving you some code, and I hope you guys can help me solve the issue.

The MainActivity:

public class MainActivity extends AppCompatActivity {
//private ArrayList<String> arrayList;
public ListView viewEvents;
DataHandler dataBase;
private ListView listView;
// SQLiteDatabase data;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listView = (ListView) findViewById(R.id.ElementsView);
    dataBase = new DataHandler(this);
    showList();
}

public void showList() {

      try{
      ArrayList<ListDisplayItems> displayList = new ArrayList<ListDisplayItems>();
      //dataBase.open();
      displayList.clear();
      //String query = "SELECT * FROM " + DataHandler.DATABASE_TABLE_DISPLAY;
      Cursor c1 = DataHandler.displayQuery();
     // Cursor c1 = data.rawQuery(query, null);
      if (c1 != null && c1.getCount() != 0) {
       if (c1.moveToFirst()) {
        do {
         ListDisplayItems listDisplayItems = new ListDisplayItems();

         listDisplayItems.SetTime(c1.getString(c1
           .getColumnIndex(DataHandler.KEY_TIME_TEXT)));
         listDisplayItems.SetName(c1.getString(c1
           .getColumnIndex(DataHandler.KEY_NAME)));
         listDisplayItems.SetDays(c1.getString(c1
           .getColumnIndex(DataHandler.KEY_DAYS_OF_WEEK_TEXT)));
         displayList.add(listDisplayItems);

        } while (c1.moveToNext());
       }
      }
      c1.close();
      //dataBase.close();

      DisplayListAdapter displayListAdapter = new DisplayListAdapter(
        MainActivity.this, displayList);
      listView.setAdapter(displayListAdapter);
      }catch(Exception e){
          e.printStackTrace();
      }

     }

The DisplayListAdapter Class:

 DataHandler database;
 Context context;
 ArrayList<ListDisplayItems> displayList;

public DisplayListAdapter(Context context, ArrayList<ListDisplayItems> list) {
    this.context = context;
    displayList = list;
}

@Override
public int getCount() {
    return displayList.size();
}

@Override
public Object getItem(int position) {
    return displayList.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup arg2) {
    ListDisplayItems displayItemsList = displayList.get(position);

    if (convertView == null){
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.item_layout, null);
    }
    TextView textTime = (TextView) convertView.findViewById(R.id.itextTime);
    textTime.setText(displayItemsList.GetTime());
    TextView textName = (TextView) convertView.findViewById(R.id.itextName);
    textName.setText(displayItemsList.GetName());
    TextView textDays = (TextView) convertView.findViewById(R.id.itextDays);
    textDays.setText(displayItemsList.GetDays());


    return convertView;
}
}

The ListDisplayItems Class:

public class ListDisplayItems {

String iName;
String iIconRing;
String iIconAlarm;
String iTimeText;
String iDaysOfWeek;

public String GetName()
{
    return iName;
}

public void SetName(String Name)
{
    this.iName = Name;
}

public String GetIconRing()
{
    return iIconRing;
}

public void SetIconRing(String Icon)
{
    this.iIconRing = Icon;
}

public String GetIconAlarm()
{
    return iIconAlarm;
}

public void SetIconAlarm(String Icon)
{
    this.iIconAlarm = Icon;
}

public String GetTime()
{
    return iTimeText;
}

public void SetTime(String Time)
{
    this.iTimeText = Time;
}

public String GetDays()
{
    return iDaysOfWeek;
}

public void SetDays(String Days)
{
    this.iDaysOfWeek = Days;
}
}

And my DataHandler Class:

public class DataHandler{
public static final String KEY_EXAMPLE = "example_of_my_keys";

static DbHelper dbhelper;
Context ctx;
static SQLiteDatabase dataBase;

public DataHandler(Context ctx){
    this.ctx = ctx;
    dbhelper = new DbHelper(ctx);
}

public static Cursor displayQuery() {
    Cursor c1 = null;
      try {

       if (dataBase.isOpen()) {
        dataBase.close();

       }
       String[] projection = {
                KEY_NAME,
                KEY_TIME_TEXT,
                KEY_DAYS_OF_WEEK_TEXT,
        };
       String sortOrder =
               KEY_ROWID + " ASC";

       dataBase = dbhelper.getWritableDatabase();
       //c1 = dataBase.rawQuery(query, null);
       c1 = dataBase.query(
                DATABASE_TABLE_DISPLAY,  // The table to query
                projection,                               // The columns to return
                null,                                // The columns for the WHERE clause
                null,                            // The values for the WHERE clause
                null,                                     // don't group the rows
                null,                                     // don't filter by row groups
                sortOrder                                 // The sort order
               );


      } catch (Exception e) {

       System.out.println("DATABASE ERROR " + e);

      }
      return c1;
}

private class DbHelper extends SQLiteOpenHelper{
           .....code creating tables and stuff///

    }
}

public DataHandler open()
{
    dataBase = dbhelper.getWritableDatabase();
    return this;
}

public void close()
{
    dbhelper.close();
}
}

I have created a custom view layout for the listView, with icons set. No errors or anything. I only get a handled NullPointer exception and nothing appears on my list.

Here is my log:

01-30 14:27:08.641: E/Trace(656): error opening trace file: No such file or directory (2) 01-30 14:27:09.419: W/dalvikvm(656): VFY: unable to find class referenced in signature (Landroid/view/SearchEvent;) 01-30 14:27:09.419: I/dalvikvm(656): Could not find method android.view.Window$Callback.onSearchRequested, referenced from method android.support.v7.view.WindowCallbackWrapper.onSearchRequested 01-30 14:27:09.429: W/dalvikvm(656): VFY: unable to resolve interface method 14535: Landroid/view/Window$Callback;.onSearchRequested (Landroid/view/SearchEvent;)Z 01-30 14:27:09.429: D/dalvikvm(656): VFY: replacing opcode 0x72 at 0x0002 01-30 14:27:09.439: I/dalvikvm(656): Could not find method android.view.Window$Callback.onWindowStartingActionMode, referenced from method android.support.v7.view.WindowCallbackWrapper.onWindowStartingActionMode 01-30 14:27:09.459: W/dalvikvm(656): VFY: unable to resolve interface method 14539: Landroid/view/Window$Callback;.onWindowStartingActionMode (Landroid/view/ActionMode$Callback;I)Landroid/view/ActionMode; 01-30 14:27:09.459: D/dalvikvm(656): VFY: replacing opcode 0x72 at 0x0002 01-30 14:27:09.989: I/dalvikvm(656): Could not find method android.view.ViewGroup.onRtlPropertiesChanged, referenced from method android.support.v7.widget.Toolbar.onRtlPropertiesChanged 01-30 14:27:09.989: W/dalvikvm(656): VFY: unable to resolve virtual method 14435: Landroid/view/ViewGroup;.onRtlPropertiesChanged (I)V 01-30 14:27:09.989: D/dalvikvm(656): VFY: replacing opcode 0x6f at 0x0007 01-30 14:27:10.069: I/dalvikvm(656): Could not find method android.content.res.TypedArray.getChangingConfigurations, referenced from method android.support.v7.widget.TintTypedArray.getChangingConfigurations 01-30 14:27:10.069: W/dalvikvm(656): VFY: unable to resolve virtual method 418: Landroid/content/res/TypedArray;.getChangingConfigurations ()I 01-30 14:27:10.079: D/dalvikvm(656): VFY: replacing opcode 0x6e at 0x0002 01-30 14:27:10.109: I/dalvikvm(656): Could not find method android.content.res.TypedArray.getType, referenced from method android.support.v7.widget.TintTypedArray.getType 01-30 14:27:10.109: W/dalvikvm(656): VFY: unable to resolve virtual method 440: Landroid/content/res/TypedArray;.getType (I)I 01-30 14:27:10.129: D/dalvikvm(656): VFY: replacing opcode 0x6e at 0x0002 01-30 14:27:10.429: I/System.out(656): DATABASE ERROR java.lang.NullPointerException 01-30 14:27:10.429: W/System.err(656): java.lang.NullPointerException 01-30 14:27:10.439: W/System.err(656): at com.teosoft.mutetimer.MainActivity.showList(MainActivity.java:55) 01-30 14:27:10.439: W/System.err(656): at com.teosoft.mutetimer.MainActivity.onCreate(MainActivity.java:27) 01-30 14:27:10.449: W/System.err(656): at android.app.Activity.performCreate(Activity.java:5008) 01-30 14:27:10.449: W/System.err(656): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 01-30 14:27:10.479: W/System.err(656): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 01-30 14:27:10.479: W/System.err(656): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 01-30 14:27:10.499: W/System.err(656): at android.app.ActivityThread.access$600(ActivityThread.java:130) 01-30 14:27:10.540: W/System.err(656): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 01-30 14:27:10.549: W/System.err(656): at android.os.Handler.dispatchMessage(Handler.java:99) 01-30 14:27:10.559: W/System.err(656): at android.os.Looper.loop(Looper.java:137) 01-30 14:27:10.559: W/System.err(656): at android.app.ActivityThread.main(ActivityThread.java:4745) 01-30 14:27:10.589: W/System.err(656): at java.lang.reflect.Method.invokeNative(Native Method) 01-30 14:27:10.589: W/System.err(656): at java.lang.reflect.Method.invoke(Method.java:511) 01-30 14:27:10.589: W/System.err(656): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 01-30 14:27:10.609: W/System.err(656): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 01-30 14:27:10.609: W/System.err(656): at dalvik.system.NativeStart.main(Native Method) 01-30 14:27:10.889: D/dalvikvm(656): GC_CONCURRENT freed 197K, 3% free 11034K/11335K, paused 115ms+53ms, total 392ms 01-30 14:27:11.949: I/Choreographer(656): Skipped 109 frames! The application may be doing too much work on its main thread. 01-30 14:27:12.029: D/gralloc_goldfish(656): Emulator without GPU emulation detected.

Sorry for the long post. I'm a newbie. :)

Possible duplicate of What is a Null Pointer Exception, and how do I fix it? — Bö macht Blau
– Bö macht Blau, Commented Jan 30, 2016 at 14:39

David Rauca · Accepted Answer · 2016-02-01 16:50:02Z

1

static SQLiteDatabase dataBase;  // this field is not initialized => dataBase = null

public DataHandler(Context ctx){
    this.ctx = ctx;
    dbhelper = new DbHelper(ctx);
}

public static Cursor displayQuery() {
    Cursor c1 = null;
    try {

       if (dataBase.isOpen()) {   // You try to use dataBase here and it is null
            dataBase.close();
       }
    ...

Replace that if block with

if (dataBase != null && dataBase.isOpen()) {  
    dataBase.close();
}

This should work.

answered Feb 1, 2016 at 16:50

David Rauca

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1 Comment

tedo2113 Over a year ago

Thanks, David! You're a pro, it worked! Thank you for your time and help! I wish you the best! :)

David Rauca · Accepted Answer · 2016-01-30 14:44:52Z

0

I think the problem is at this line:

c1.close();

c1 seems to be null and you try to close it even if it is null

if (c1 != null && c1.getCount() != 0) {
    // code
}
c1.close();

Move that line inside if block and the app shouldn't crash. But the list will be empty.

answered Jan 30, 2016 at 14:44

David Rauca

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6 Comments

tedo2113 Over a year ago

Thanks, man. I guess that worked. Exception is gone. But i still don't have a populated list view. Any idea why? And how can I fix it? I've been trying for weeks now...

David Rauca Over a year ago

You're welcome! The problem seems to be in the method displayQuery. The app actually crashes there but because of that try catch block the app doesn't crash. Could you attach the code for DbHelper? Also, instead of System.out.println("DATABASE ERROR " + e); do e.printStackTrace(); and attach the log.

tedo2113 Over a year ago

I posted it as an answer below.

David Rauca Over a year ago

What is in the line 51 from DataHandler?

tedo2113 Over a year ago

Sorry, could you be more specific? Which line do you mean? The if statement or the Sort Ordrer?

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