CODEWITHSUNDEEP
androidlistviewexception
tedo2113
tedo2113

Reputation: 89

Android ListView Null Pointer exception

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. :)

Upvotes: 0

Views: 366

Answers (2)

David Rauca
David Rauca

Reputation: 1583

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.

Upvotes: 1

David Rauca
David Rauca

Reputation: 1583

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.

Upvotes: 0

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