android - Can't instantiate class, no empty constructor, SQLiteHelper -
i'm trying android application using sqlite when try launch application on smartphone, appears white screen , crash.
so have looked @ logcat , showed errors:
04-18 01:33:32.186: e/androidruntime(26741): fatal exception: main 04-18 01:33:32.186: e/androidruntime(26741): java.lang.runtimeexception: unable instantiate activity componentinfo{com.example.sqliteexample/database.mysqlitehelper}: java.lang.instantiationexception: can't instantiate class database.mysqlitehelper; no empty constructor 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.activitythread.performlaunchactivity(activitythread.java:2034) 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.activitythread.handlelaunchactivity(activitythread.java:2135) 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.activitythread.access$700(activitythread.java:140) 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.activitythread$h.handlemessage(activitythread.java:1237) 04-18 01:33:32.186: e/androidruntime(26741): @ android.os.handler.dispatchmessage(handler.java:99) 04-18 01:33:32.186: e/androidruntime(26741): @ android.os.looper.loop(looper.java:137) 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.activitythread.main(activitythread.java:4921) 04-18 01:33:32.186: e/androidruntime(26741): @ java.lang.reflect.method.invokenative(native method) 04-18 01:33:32.186: e/androidruntime(26741): @ java.lang.reflect.method.invoke(method.java:511) 04-18 01:33:32.186: e/androidruntime(26741): @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:1027) 04-18 01:33:32.186: e/androidruntime(26741): @ com.android.internal.os.zygoteinit.main(zygoteinit.java:794) 04-18 01:33:32.186: e/androidruntime(26741): @ dalvik.system.nativestart.main(native method) 04-18 01:33:32.186: e/androidruntime(26741): caused by: java.lang.instantiationexception: can't instantiate class database.mysqlitehelper; no empty constructor 04-18 01:33:32.186: e/androidruntime(26741): @ java.lang.class.newinstanceimpl(native method) 04-18 01:33:32.186: e/androidruntime(26741): @ java.lang.class.newinstance(class.java:1319) 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.instrumentation.newactivity(instrumentation.java:1068) 04-18 01:33:32.186: e/androidruntime(26741): @ android.app.activitythread.performlaunchactivity(activitythread.java:2025) 04-18 01:33:32.186: e/androidruntime(26741): ... 11 more here mysqlitehelper class:
package database; import android.util.log; import android.annotation.suppresslint; import android.content.context; import android.database.databaseerrorhandler; import android.database.sqlite.sqlitedatabase; import android.database.sqlite.sqlitedatabase.cursorfactory; import android.database.sqlite.sqliteopenhelper; @suppresslint("newapi") public class mysqlitehelper extends sqliteopenhelper { public static final string table_comments = "comments"; public static final string column_id = "_id"; public static final string column_comment = "comment"; private static final string database_name = "commments.db"; private static final int database_version = 1; // database creation sql statement private static final string database_create = "create table " + table_comments + "(" + column_id + " integer primary key autoincrement, " + column_comment + " text not null);"; public mysqlitehelper(context context) { super(context, database_name, null, database_version); } @override public void oncreate(sqlitedatabase database) { database.execsql(database_create); } @override public void onupgrade(sqlitedatabase db, int oldversion, int newversion) { log.w(mysqlitehelper.class.getname(), "upgrading database version " + oldversion + " " + newversion + ", destroy old data"); db.execsql("drop table if exists " + table_comments); oncreate(db); } } here testdatabaseactivity class:
package activity; import java.util.list; import java.util.random; import model.comment; import dao.commentsdatasource; import android.app.listactivity; import android.os.bundle; import android.view.view; import android.widget.arrayadapter; import com.example.sqliteexample.r; public class testdatabaseactivity extends listactivity { private commentsdatasource datasource; public testdatabaseactivity(){ super(); } @override public void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_my_sqlite_helper); datasource = new commentsdatasource(this); datasource.open(); list<comment> values = datasource.getallcomments(); // use simplecursoradapter show // elements in listview arrayadapter<comment> adapter = new arrayadapter<comment>(this, android.r.layout.simple_list_item_1, values); setlistadapter(adapter); } // called via onclick attribute // of buttons in main.xml public void onclick(view view) { @suppresswarnings("unchecked") arrayadapter<comment> adapter = (arrayadapter<comment>) getlistadapter(); comment comment = null; switch (view.getid()) { case r.id.add: string[] comments = new string[] { "cool", "very nice", "hate it" }; int nextint = new random().nextint(3); // save new comment database comment = datasource.createcomment(comments[nextint]); adapter.add(comment); break; case r.id.delete: if (getlistadapter().getcount() > 0) { comment = (comment) getlistadapter().getitem(0); datasource.deletecomment(comment); adapter.remove(comment); } break; } adapter.notifydatasetchanged(); } @override protected void onresume() { datasource.open(); super.onresume(); } @override protected void onpause() { datasource.close(); super.onpause(); } } commentsdatasource class:
import java.util.arraylist; import java.util.list; import database.mysqlitehelper; import model.comment; import android.content.contentvalues; import android.content.context; import android.database.cursor; import android.database.sqlexception; import android.database.sqlite.sqlitedatabase; public class commentsdatasource { private sqlitedatabase database; private mysqlitehelper dbhelper; private string[] allcolumns = { mysqlitehelper.column_id, mysqlitehelper.column_comment }; public commentsdatasource(context context) { dbhelper = new mysqlitehelper(context); } public void open() throws sqlexception { database = dbhelper.getwritabledatabase(); } public void close() { dbhelper.close(); } public comment createcomment(string comment) { contentvalues values = new contentvalues(); values.put(mysqlitehelper.column_comment, comment); long insertid = database.insert(mysqlitehelper.table_comments, null, values); cursor cursor = database.query(mysqlitehelper.table_comments, allcolumns, mysqlitehelper.column_id + " = " + insertid, null, null, null, null); cursor.movetofirst(); comment newcomment = cursortocomment(cursor); cursor.close(); return newcomment; } public void deletecomment(comment comment) { long id = comment.getid(); system.out.println("comment deleted id: " + id); database.delete(mysqlitehelper.table_comments, mysqlitehelper.column_id + " = " + id, null); } public list<comment> getallcomments() { list<comment> comments = new arraylist<comment>(); cursor cursor = database.query(mysqlitehelper.table_comments, allcolumns, null, null, null, null, null); cursor.movetofirst(); while (!cursor.isafterlast()) { comment comment = cursortocomment(cursor); comments.add(comment); cursor.movetonext(); } // make sure close cursor cursor.close(); return comments; } private comment cursortocomment(cursor cursor) { comment comment = new comment(); comment.setid(cursor.getlong(0)); comment.setcomment(cursor.getstring(1)); return comment; } } i have found java.lang.instantiationexception: can't instantiate class database.mysqlitehelper; no empty constructor, don't know how fix it..
the error clear - didn't write no-arg constructor, yet code requires one.
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