java - Android: erro NullPointerException on getWritableDatabase() -

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this question has answer here:

i have problem nullpointerexception on getwritabledatabase()

database

i trying build small application store information in sqlite table. receive "java.lang.nullpointerexception" exception in getwritabledatabase method. can me? code below.

public class pacientedatabase extends sqliteopenhelper {  private static final string db_name = "paciente.sqlite"; private static final int version = 1; private static final string table = "paciente";   public pacientedatabase(context context) {     super(context, db_name, null, version); }  @override public void oncreate(sqlitedatabase db) {     // crear tabla paciente     db.execsql("create table paciente (" +             "_id integer primary key autoincrement, start_date integer)"); }  @override public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {  }

}

activiy 

public class registropaciente extends actionbaractivity {  private button mbotonok;  private pacientedatabase mpaciente; private context c;   @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_registro_paciente);     mpaciente = new pacientedatabase(c);      mbotonok = (button)findviewbyid(r.id.boton_registro_ok);       mbotonok.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {              contentvalues datos = new contentvalues();              datos.put("start_date", 1000 );              mpaciente.getwritabledatabase().insert("paciente", null, datos);              finish();         }     }); }

error in log cat

03-16 22:22:46.531    1181-1181/com.example.franciscodelgadogarcia.projecto e/androidruntime﹕ fatal exception: main process: com.example.franciscodelgadogarcia.projecto, pid: 1181 java.lang.nullpointerexception         @ android.database.sqlite.sqliteopenhelper.getdatabaselocked(sqliteopenhelper.java:224)         @ android.database.sqlite.sqliteopenhelper.getwritabledatabase(sqliteopenhelper.java:164)         @ com.example.franciscodelgadogarcia.projecto.registropaciente$1.onclick(registropaciente.java:84)         @ android.view.view.performclick(view.java:4438)         @ android.view.view$performclick.run(view.java:18422)         @ android.os.handler.handlecallback(handler.java:733)         @ android.os.handler.dispatchmessage(handler.java:95)         @ android.os.looper.loop(looper.java:136)         @ android.app.activitythread.main(activitythread.java:5017)         @ java.lang.reflect.method.invokenative(native method)         @ java.lang.reflect.method.invoke(method.java:515)         @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:779)         @ com.android.internal.os.zygoteinit.main(zygoteinit.java:595)         @ dalvik.system.nativestart.main(native method)

c object of context null initialize before passing cto pacientedatabase class constructor :

 c=registropaciente.this  mpaciente = new pacientedatabase(c);

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