Database table is not showing in SQLite Android

Question

Here I am making the function of Database Cursor which is to be used frequently in the project.

Here is my code in DAL:

public Cursor SelectQuery(String table){
  Cursor cursor=SQLiteDb.query(table,null,null,null,null,null,null,null);
  return cursor;
}

By debugging SQLiteDB is getting null in the mainactivity.

Code:

Cursor c=dal.SelectQuery(ConstantsValues.TabData);
Log.e("hello111",""+c.getCount());

So as to get total rows But the table is not coming.Here ConstantsValues.TabData is having table name.
Where as in here code:

public ArrayList AllSelectQryForTabEmpData1() {
  ArrayList<Employee> data = new ArrayList();

  Cursor cursor = SQLiteDb.query(ConstantsValues.TabData, null, null, null, null, null, null, null);
  while (cursor.moveToNext()) {
    String id = cursor.getString(cursor.getColumnIndex(ConstantsValues.ID));
    String name = cursor.getString(cursor.getColumnIndex(ConstantsValues.NAME));
    String value= cursor.getString(cursor.getColumnIndex(ConstantsValues.VALUE));

    data.add(new Employee(id, name,value));
  }
  cursor.close();
  return data;
}

Here is open and close code:

public void OpenDB() {
  SQLiteDb = new DBHelper(context).getWritableDatabase();
}

public void CloseDB() {
  if (SQLiteDb.isOpen()) {
     SQLiteDb.close();
  }
}

I am getting Table in SQLiteDb. It seems something is wrong in making Cursor.

Here is my logcat:

E/AndroidRuntime: FATAL EXCEPTION: main
                                                                             Process: com.example.abhishek.httpclient, PID: 12538
                                                                             java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.abhishek.httpclient/com.example.abhishek.httpclient.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.query(java.lang.String, java.lang.String[], java.lang.String, java.lang.String[], java.lang.String, java.lang.String, java.lang.String, java.lang.String)' on a null object reference
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2671)
                                                                                 at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1501)
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:111)
                                                                                 at android.os.Looper.loop(Looper.java:207)
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5769)
                                                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:681)
                                                                              Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.query(java.lang.String, java.lang.String[], java.lang.String, java.lang.String[], java.lang.String, java.lang.String, java.lang.String, java.lang.String)' on a null object reference
                                                                                 at com.example.abhishek.httpclient.DAL.SelectQuery(DAL.java:141)
                                                                                 at com.example.abhishek.httpclient.MainActivity.onCreate(MainActivity.java:92)
                                                                                 at android.app.Activity.performCreate(Activity.java:6317)
                                                                                 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2532)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2671) 
                                                                                 at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1501) 
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:111) 
                                                                                 at android.os.Looper.loop(Looper.java:207) 
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5769) 
                                                                                 at java.lang.reflect.Method.invoke(Native Method) 
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791) 
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:681)

Just an advice, please use lowercase for the first later for variable object name and uppercase for Class name. same condition for the method name too. It will help you on maintaining your code. — ישו אוהב אותך, Oct 26 '16 at 07:51

ישו אוהב אותך · Answer 1 · 2016-10-26T08:04:47.903

You need to instantiate SQLiteDatabase first, something like this:

// Create and/or open the database for writing
SQLiteDatabase db = getWritableDatabase();

UPDATE:

For a simple fix, you can change your openDB() method to (note: not tested):

public void openDB() {
  if(sqliteDB == null) {
    sqliteDB= new DBHelper(context).getWritableDatabase();
  } else {
    if(!sqliteDB.isOpen(){
       // reopen again. 
       // NOTE: This should be changed to the method which you use to open the db.
       sqliteDB= new DBHelper(context).getWritableDatabase();
    }
  }
}

Then call it every time you use the SQLiteDb, something like this:

openDB();
Cursor cursor = SQLiteDb.query(ConstantsValues.TabData, null, null,
                                null, null, null, null, null);
...

minhazur · Accepted Answer · 2016-10-26T07:46:28.777

2

I think there is something wrong with database connection. Please, follow this tutorial specially DBHelper.java class. How they have made database connection. https://www.tutorialspoint.com/android/android_sqlite_database.htm

SQLiteDatabase db = this.getWritableDatabase();

By using getWritableDatabase(), you have the power to do both read and write operation to your db.

edited Oct 26 '16 at 07:46

answered Oct 26 '16 at 07:41

minhazur

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Well my other code in AllSelectQryForTabEmpData1() its working fine.....but not this yet i will try – Abhi Oct 26 '16 at 07:45
I think, those code snippet are taken from two different java class. May be, in one you have created connection but in other not. @Abhi – minhazur Oct 26 '16 at 07:51
Yes i had just initialised it in other java class...**arr_emp** = ban.AllSelectQryForTabEmpData1(); – Abhi Oct 26 '16 at 07:53
please, make sure you have established connection before using SQLiteDB. If needed, call openDb() method again. – minhazur Oct 26 '16 at 07:55
1

you were right Thank you :) 1 vote for that.. :) – Abhi Oct 26 '16 at 07:58

Database table is not showing in SQLite Android

2 Answers2