Why can't my Android app see the database file? -

i'm creating android app, , want make registration. have written file c.r.u.d database. when start app , try add somebody, can see popup message:

"unfortunately , application has been stopped".  

here database controller code:

package com.example.lingwista.lingwista;  import android.content.contentvalues; import android.content.context; import android.database.cursor; import android.database.sqlite.sqlitedatabase; import android.database.sqlite.sqliteopenhelper;  public class db_controller extends sqliteopenhelper { public db_controller(context context, string name, sqlitedatabase.cursorfactory factory, int version) {     super(context, "lingwista.db", factory, version); }  @override public void oncreate(sqlitedatabase db) {     db.execsql("create table users( id integer primary key autoincrement, username text unique, password text);"); }  @override public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {     db.execsql("drop table if exists users;"); }  public void insert_user(string username, string password){     contentvalues contentvalues = new contentvalues();     contentvalues.put("username",username);     contentvalues.put("password",password);     this.getwritabledatabase().insertorthrow("users", "", contentvalues); }   public boolean search_user(string username){     cursor cursor = this.getreadabledatabase().rawquery("select username users",null);     while (cursor.movetonext()){         if(cursor.getstring(1).equals(username)){             return true;         }     }     return false; }  public boolean search_password(string password){     cursor cursor = this.getreadabledatabase().rawquery("select password users",null);     while (cursor.movetonext()){         if(cursor.getstring(1).equals(password)){             return true;         }     }     return false; } 

}

this java file use controller:

package com.example.lingwista.lingwista;  import android.content.context; import android.content.intent; import android.os.bundle; import android.support.design.widget.floatingactionbutton; import android.support.design.widget.snackbar; import android.support.v7.app.appcompatactivity; import android.support.v7.widget.toolbar; import android.view.view; import android.widget.edittext; import android.widget.toast;  public class rejestracja extends appcompatactivity { db_controller controller; edittext username; edittext password1; edittext password2; string login; string haslo1; string haslo2;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_rejestracja);     toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar);     setsupportactionbar(toolbar);     username = (edittext)findviewbyid(r.id.edittext3);     password1 = (edittext)findviewbyid(r.id.edittext4);     password2 = (edittext)findviewbyid(r.id.edittext5);     controller = new db_controller(this, "", null, 1); }  public void gotomenu(view view) {     login = username.gettext().tostring();     haslo1 = password1.gettext().tostring();     haslo2 = password2.gettext().tostring();      boolean u;      string message;     context context = getapplicationcontext();     int duration = toast.length_short;      if(haslo1.equals(haslo2)){         u = controller.search_user(login);          if(u==true){             message = "istnieje już użytkownik który korzysta z tego adresu email";             toast toast = toast.maketext(context,message, duration);             toast.show();         }         else{             controller.insert_user(login,haslo1);             intent intent = new intent(".menu");             startactivity(intent);         }       }else{         message = "błąd hasła. proszę upewnić się ze oba pola zawierają samo hasło";         toast toast = toast.maketext(context,message, duration);         toast.show();     }     if(login.equals("") || haslo1.equals("") || haslo2.equals("")){         message = "wszystkie pola muszą być wypełnione !";         toast toast = toast.maketext(context,message, duration);         toast.show();     } }  @override public void onpause(){     super.onpause();     finish(); }  public void back(view view) {     intent intent =new intent(".mainmenuactivity");     startactivity(intent); }  public void exitapp(view view) {     system.exit(0); } } 

and content.xml:

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingbottom="@dimen/activity_vertical_margin" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" app:layout_behavior="@string/appbar_scrolling_view_behavior" tools:context="com.example.lingwista.lingwista.rejestracja" tools:showin="@layout/activity_rejestracja">  <imageview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/imageview2"     android:layout_alignparenttop="true"     android:src="@drawable/lingwista"     android:layout_centerhorizontal="true" />  <textview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:textappearance="?android:attr/textappearancelarge"     android:text="rejestracja"     android:id="@+id/textview3"     android:layout_below="@+id/imageview2"     android:layout_centerhorizontal="true"     android:textcolor="#00ff00"     android:layout_margintop="30dp"     android:textsize="38dp" />  <edittext     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:inputtype="textemailaddress"     android:ems="10"     android:id="@+id/edittext3"     android:layout_below="@+id/textview3"     android:layout_margintop="10dp"     android:layout_centerhorizontal="true"     android:autotext="false"     android:hint="adres email"     android:backgroundtint="#0000ff" />  <edittext     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:inputtype="textpassword"     android:ems="10"     android:id="@+id/edittext4"     android:layout_below="@+id/edittext3"     android:layout_margintop="5dp"     android:layout_centerhorizontal="true"     android:hint="hasło"     android:backgroundtint="#0000ff" />  <edittext     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:inputtype="textpassword"     android:ems="10"     android:id="@+id/edittext5"     android:layout_below="@+id/edittext4"     android:layout_alignright="@+id/edittext4"     android:layout_margintop="5dp"     android:layout_alignend="@+id/edittext4"     android:hint="powtorz hasło"     android:backgroundtint="#0000ff" />  <button     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="zarejestruj"     android:id="@+id/button12"     android:layout_margintop="52dp"     android:layout_below="@+id/edittext5"     android:layout_centerhorizontal="true"     android:textcolor="#ffffff"     android:textsize="20dp"     android:background="#0000ff"     android:onclick="gotomenu"/> </relativelayout> 

this error log:

01-16 02:55:10.539 18767-18791/com.example.lingwista.lingwista e/surface: getslotfrombufferlocked: unknown buffer: 0xab855e50 01-16 02:55:13.104 18767-18767/com.example.lingwista.lingwista e/cursorwindow: failed read row 0, column 1 cursorwindow has 1 rows, 1 columns. 01-16 02:55:13.104 18767-18767/com.example.lingwista.lingwista d/androidruntime: shutting down vm 01-16 02:55:13.104 18767-18767/com.example.lingwista.lingwista e/androidruntime: fatal exception: main process: com.example.lingwista.lingwista, pid: 18767 java.lang.illegalstateexception: not execute method android:onclick  @ android.support.v7.app.appcompatviewinflater$declaredonclicklistener.onclick(appcompatviewinflater.java:275)  @ android.view.view.performclick(view.java:5198)  @ android.view.view$performclick.run(view.java:21147)  @ android.os.handler.handlecallback(handler.java:739)  @ android.os.handler.dispatchmessage(handler.java:95)  @ android.os.looper.loop(looper.java:148)  @ android.app.activitythread.main(activitythread.java:5417)  @ java.lang.reflect.method.invoke(native method)  @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726)  @ com.android.internal.os.zygoteinit.main(zygoteinit.java:616) caused by: java.lang.reflect.invocationtargetexception  @ java.lang.reflect.method.invoke(native method)  @ android.support.v7.app.appcompatviewinflater$declaredonclicklistener.onclick(appcompatviewinflater.java:270)  @ android.view.view.performclick(view.java:5198)   @ android.view.view$performclick.run(view.java:21147)   @ android.os.handler.handlecallback(handler.java:739)   @ android.os.handler.dispatchmessage(handler.java:95)   @ android.os.looper.loop(looper.java:148)   @ android.app.activitythread.main(activitythread.java:5417)   @ java.lang.reflect.method.invoke(native method)   @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726)   @ com.android.internal.os.zygoteinit.main(zygoteinit.java:616)  caused by: java.lang.illegalstateexception: couldn't read row 0, col 1 cursorwindow.  make sure cursor initialized correctly before accessing data it.  @ android.database.cursorwindow.nativegetstring(native method)  @ android.database.cursorwindow.getstring(cursorwindow.java:438)  @ android.database.abstractwindowedcursor.getstring(abstractwindowedcursor.java:51)  @ com.example.lingwista.lingwista.db_controller.search_user(db_controller.java:35)  @ com.example.lingwista.lingwista.rejestracja.gotomenu(rejestracja.java:47)  @ java.lang.reflect.method.invoke(native method)   @ android.support.v7.app.appcompatviewinflater$declaredonclicklistener.onclick(appcompatviewinflater.java:270)   @ android.view.view.performclick(view.java:5198)   @ android.view.view$performclick.run(view.java:21147)   @ android.os.handler.handlecallback(handler.java:739)   @ android.os.handler.dispatchmessage(handler.java:95)   @ android.os.looper.loop(looper.java:148)   @ android.app.activitythread.main(activitythread.java:5417)   @ java.lang.reflect.method.invoke(native method)   @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726)   @ com.android.internal.os.zygoteinit.main(zygoteinit.java:616)  01-16 02:55:19.507 18767-18767/? i/process: sending signal. pid: 18767 sig: 9 

the error clear:

caused by: java.lang.illegalstateexception: couldn't read row 0, col 1 cursorwindow.  make sure cursor initialized correctly before accessing data it.  @ android.database.cursorwindow.nativegetstring(native method)  @ android.database.cursorwindow.getstring(cursorwindow.java:438)  @ android.database.abstractwindowedcursor.getstring(abstractwindowedcursor.java:51)  @ com.example.lingwista.lingwista.db_controller.search_user(db_controller.java:35) 

here's offending code that's crashing:

public boolean search_user(string username){     cursor cursor = this.getreadabledatabase().rawquery("select username users",null);     while (cursor.movetonext()){         if(cursor.getstring(1).equals(username)){             return true;         }     }     return false; } 

the columns have zero-based index , asking 1 column in query. such should cursor.getstring(0)

cursor.getstring(int columnindex) documentation:

returns value of requested column string.

the result , whether method throws exception when column value null or column type not string type implementation-defined.

parameters

columnindex - zero-based index of target column.

returns

the value of column string.

also note written null reference if use correct column. want like:

if (!cursor.isnull(0) && cursor.getstring(0).equals(username)) {