Custom adapter with SQLite

Question

I want to put data in customer adapter from my sqlite

this is my code custom adapter I want to use BaseAdapter with sqlite to display information

public class Myadapter extends BaseAdapter{
Context context;
ArrayList<String>mylist;
private static LayoutInflater inflater=null;
public Myadapter(Context context, int element,ArrayList<String>mylist) {
    // TODO Auto-generated constructor stub
    this.mylist=mylist;
    this.context=context;
    inflater = ( LayoutInflater )context.
            getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    //return result.length;
    return  mylist.size();
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return mylist.get(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

public class Holder {
    TextView t1;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    SQLiteDatabase sq;
    // TODO Auto-generated method stub
    Holder holder=new Holder();
    View rowView;
    rowView = inflater.inflate(R.layout.element, parent,false);
    final   TextView t1=(TextView) rowView.findViewById(R.id.t1);
    //Viwe.info.get(position);


    return rowView;
}

know i want to display result in cutome layout this is viwe activity

public class Viwe extends AppCompatActivity {
public static  SQLiteDatabase db;
public ListView l1;
public static ArrayList<String> information;
// public String[] salfi={"moh","mas"};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_viwe);
    l1 = (ListView) findViewById(R.id.l1);

    db = openOrCreateDatabase("info", MODE_PRIVATE, null);
    // ArrayAdapter<String>data=new ArrayAdapter<String>(Viwe.this,android.R.layout.simple_list_item_1,salfi);
    Myadapter myadapter = new Myadapter(Viwe.this, R.layout.element, information);


    //Myadapter myadapter=new Myadapter(Viwe.this,R.layout.element,info);

    try {

            Viwe.getall();

    } catch (Exception e) {
        e.printStackTrace();
        Log.d("tage", e.getMessage());

    }
    l1.setAdapter(myadapter);
    myadapter.notifyDataSetChanged();



}
public  static void getall()
{

    Cursor c = db.rawQuery("select * from information", null);
    while (c.moveToNext())

    {
        information.add(c.getString(0));
    }
    c.close();
}

my logcat

05-18 00:18:27.516 27670-27670/com.example.dv_loper.db E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.example.dv_loper.db, PID: 27670
                                                                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dv_loper.db/com.example.dv_loper.db.Viwe}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2442)
                                                                         at android.app.ActivityThread.access$800(ActivityThread.java:156)
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1351)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                         at android.os.Looper.loop(Looper.java:211)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5389)
                                                                         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:1020)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815)
                                                                      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
                                                                         at com.example.dv_loper.db.Myadapter.getCount(Myadapter.java:36)
                                                                         at android.widget.ListView.setAdapter(ListView.java:487)
                                                                         at com.example.dv_loper.db.Viwe.onCreate(Viwe.java:45)
                                                                         at android.app.Activity.performCreate(Activity.java:5990)
                                                                         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2332)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2442) 
                                                                         at android.app.ActivityThread.access$800(ActivityThread.java:156) 
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1351) 
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                         at android.os.Looper.loop(Looper.java:211) 
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5389) 
                                                                         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:1020) 
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815) 

Answer 1

You have a simple problem, when you first initialize the Adapter you pass to it an empty ArrayList .... because the try-catch block is coming after the initialization of the adapter and the information ArrayList is null, so simply put the initialization after your Array get filled like this :

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_viwe);
    l1 = (ListView) findViewById(R.id.l1);

    db = openOrCreateDatabase("info", MODE_PRIVATE, null);

    try {

            Viwe.getall();
           // information arraylist got filled here

    } catch (Exception e) {
        e.printStackTrace();
        Log.d("tage", e.getMessage());

    }

    Myadapter myadapter = new Myadapter(Viwe.this, R.layout.element,information);
    //the information is not null  here as before in your code
    l1.setAdapter(myadapter);
    myadapter.notifyDataSetChanged();

}

and that's pretty much it :)

Edit:

when I saw your code I thought you were initializing the ArrayList in the getall() method and everything was fine, but that was not right, you are not initializing it at all , this is what getall method should look like :

public  static void getall()
{
    // this is the missing initialization

    information = new ArrayList<String>();

    Cursor c = db.rawQuery("select * from information", null);
    while (c.moveToNext())

    {
        information.add(c.getString(0));
    }
    c.close();
}