I'm new, I am doing some debugging. I am having some difficulty that I am having some difficulty conveying.
I am trying to read from a SQLite database I have created in another activity.
My current problem appears to be:
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
which should point to my database helper class.
public class SecondActivity extends ListActivity {
CustomOpenHelper myOpenHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
displayDataInTable();
}
void displayDataInTable() {
List<String> values = queryTable();
if (values != null) {
ArrayAdapter<String> adapter = new ArrayAdapter<String>(SecondActivity.this, android.R.layout.simple_list_item_1, values);
setListAdapter(adapter);
}
}
List<String> queryTable() {
List<String> player = new ArrayList<String>();
SQLiteDatabase db = myOpenHelper.getReadableDatabase();
Cursor cursor = db.query(true, CustomOpenHelper.TABLE_NAME, new String[]{"_id, name, score"}, null, null, null, null, null, null, null);
while (cursor.moveToNext()) {
int id = cursor.getInt(cursor.getColumnIndex("_id"));
String name = cursor.getString(cursor.getColumnIndex("name"));
int score = cursor.getInt(cursor.getColumnIndex("score"));
player.add(id + " --> the player " + name + " has got a score of " + score + "s");
}
return player;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_second, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
The LogCat error (extract):
09-28 20:41:57.039 1271-1285/system_process W/ActivityManager﹕ Launch timeout has expired, giving up wake lock!
09-28 20:42:23.468 3642-3642/com.example.eagle.sqlite2activitytest D/AndroidRuntime﹕ Shutting down VM
09-28 20:42:23.486 3642-3642/com.example.eagle.sqlite2activitytest E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.eagle.sqlite2activitytest, PID: 3642
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.eagle.sqlite2activitytest/com.example.eagle.sqlite2activitytest.SecondActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.example.eagle.sqlite2activitytest.CustomOpenHelper.getReadableDatabase()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.example.eagle.sqlite2activitytest.CustomOpenHelper.getReadableDatabase()' on a null object reference
at com.example.eagle.sqlite2activitytest.SecondActivity.queryTable(SecondActivity.java:43)
at com.example.eagle.sqlite2activitytest.SecondActivity.displayDataInTable(SecondActivity.java:29)
at com.example.eagle.sqlite2activitytest.SecondActivity.onCreate(SecondActivity.java:24)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
09-28 20:42:23.493 1271-1721/system_process W/ActivityManager﹕ Force finishing activity com.example.eagle.sqlite2activitytest/.SecondActivity
What do you think?
try this you can create proper object like this.
CustomOpenHelper myOpenHelper = new CustomOpenHelper(this);
and then write following statement,
SQLiteDatabase db = myOpenHelper.getReadableDatabase();