Failed to get Listview to update from database.

Question

No matter what I seem to be trying to do with this list and trying to dynamically update it, when I click the button, it does not work and always throws NPE.

The code is below and I really welcome the help. I tried the request and I tried notifyDataSetChanged, but I will be honest, this is only my second project and the first that uses a database or list, and I will fight.

DatabaseHelper

import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.provider.BaseColumns; import android.util.Log; public class DatabaseHelper extends SQLiteOpenHelper { private static final String TAG = DatabaseHelper.class.getSimpleName(); public static final String DATABASE_NAME = "reordermymeds.db"; public static final int DATABASE_VERSION = 3; public static final String TABLE_NAME = "Medicines"; public static final String C_ID = BaseColumns._ID; public static final String C_MED_NAME = "med_name"; public static final String TABLE_NAME_SURG = "Surgeries"; public static final String SURGERY_NAME = "sName"; public static final String SURGERY_TEL = "sTel"; public static final String SURGERY_MAIL = "sMail"; public DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); // TODO Auto-generated constructor stub } @Override public void onCreate(SQLiteDatabase db) { // TODO Auto-generated method stub String sql = String.format("CREATE TABLE %s (%s INTEGER PRIMARY KEY, %s TEXT)", TABLE_NAME, C_ID, C_MED_NAME); String sql_surg = String.format( "create table %s (%s int primary key, %s TEXT, %s TEXT, %s TEXT)", TABLE_NAME_SURG, C_ID, SURGERY_NAME, SURGERY_TEL, SURGERY_MAIL); Log.d(TAG, "onCreate sql: "+sql); db.execSQL(sql); db.execSQL(sql_surg); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // TODO Auto-generated method stub db.execSQL("drop table if exists " + TABLE_NAME); db.execSQL("drop table if exists " + TABLE_NAME_SURG); this.onCreate(db); } } 

and

Activities

 import android.app.ListActivity; import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.SimpleCursorAdapter; import android.widget.Toast; public class pills extends ListActivity { public static final String C_MED_NAME = "med_name"; public SimpleCursorAdapter ladapter; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.pills); try { DatabaseHelper DBHelper= new DatabaseHelper(this); SQLiteDatabase db = DBHelper.getReadableDatabase(); Cursor cur = db.query("Medicines", null, null, null, null, null, null); startManagingCursor(cur); String [] columns = new String[] {C_MED_NAME}; int [] to = new int[] {R.id.meditem}; SimpleCursorAdapter ladapter = new SimpleCursorAdapter(this, R.layout.meditem, cur, columns, to); this.setListAdapter(ladapter); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } Button saveMed = (Button) findViewById(R.id.pills_newmedsubmit); saveMed.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub final EditText newMed = (EditText) findViewById(R.id.pills_newmedtxtbox); if (newMed.getText().toString().equals("")) { Context context = getApplicationContext(); CharSequence text = "Please type the name of a new prescription item."; int duration = Toast.LENGTH_SHORT; Toast toast= Toast.makeText(context, text, duration); toast.show(); } else { String medName = newMed.getText().toString(); insertNewPrescriptionItem(medName); EditText clearTextBox = (EditText) findViewById(R.id.pills_newmedtxtbox); clearTextBox.setText(""); Context context = getApplicationContext(); CharSequence text = "Saved"; int duration = Toast.LENGTH_SHORT; Toast toast = Toast.makeText(context, text, duration); toast.show(); } setListAdapter(ladapter); ladapter.notifyDataSetChanged(); } });} private void insertNewPrescriptionItem (String medName){ DatabaseHelper DbHelper = new DatabaseHelper(this); SQLiteDatabase db = DbHelper.getWritableDatabase(); ContentValues cv = new ContentValues(); cv.put(DatabaseHelper.C_MED_NAME, medName); db.insert(DatabaseHelper.TABLE_NAME, DatabaseHelper.C_MED_NAME, cv); db.close(); } } 

and, of course, the last, but no less important, stack trace. I see a line with an error, but everything that I tried to use Google leads to the same. Can anyone show that I have to go stupidly wrong?

Stack trace

 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): FATAL EXCEPTION: main 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): java.lang.NullPointerException 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at com.asurya.reordmymeds.pills$1.onClick(pills.java:90) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.view.View.performClick(View.java:2485) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.view.View$PerformClick.run(View.java:9080) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.os.Handler.handleCallback(Handler.java:587) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.os.Handler.dispatchMessage(Handler.java:92) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.os.Looper.loop(Looper.java:130) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.app.ActivityThread.main(ActivityThread.java:3683) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at java.lang.reflect.Method.invokeNative(Native Method) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at java.lang.reflect.Method.invoke(Method.java:507) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at dalvik.system.NativeStart.main(Native Method) 08-11 01:21:26.107: WARN/ActivityManager(110): Force finishing activity com.asurya.reordmymeds/.pills 

Unfortunately. It would help if I let you know everything, and not consider them to be myself :)

The line of code that calls NPE is:

 ladapter.notifyDataSetChanged(); 

In addition, if I just comment out this line, the application works fine, but you need to update the Activity to see the updated data in the database. Thanks to everyone.

Answer 1

  import android.app.ListActivity; import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.SimpleCursorAdapter; import android.widget.Toast; public class pills extends ListActivity { public static final String C_MED_NAME = "med_name"; public SimpleCursorAdapter ladapter; Context context; Cursor cur; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.pills); context=this; try { DatabaseHelper DBHelper= new DatabaseHelper(this); SQLiteDatabase db = DBHelper.getReadableDatabase(); cur = db.query("Medicines", null, null, null, null, null, null); startManagingCursor(cur); String [] columns = new String[] {C_MED_NAME}; int [] to = new int[] {R.id.meditem}; ladapter = new SimpleCursorAdapter(this, R.layout.meditem, cur, columns, to); this.setListAdapter(ladapter); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } Button saveMed = (Button) findViewById(R.id.pills_newmedsubmit); saveMed.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub final EditText newMed = (EditText) findViewById(R.id.pills_newmedtxtbox); if (newMed.getText().toString().equals("")) { // Context context = getApplicationContext(); CharSequence text = "Please type the name of a new prescription item."; int duration = Toast.LENGTH_SHORT; Toast toast= Toast.makeText(context, text, duration); toast.show(); } else { String medName = newMed.getText().toString(); insertNewPrescriptionItem(medName); EditText clearTextBox = (EditText) findViewById(R.id.pills_newmedtxtbox); clearTextBox.setText(""); // Context context = getApplicationContext(); CharSequence text = "Saved"; int duration = Toast.LENGTH_SHORT; Toast toast = Toast.makeText(context, text, duration); toast.show(); } refresh(); } });} private void insertNewPrescriptionItem (String medName){ DatabaseHelper DbHelper = new DatabaseHelper(this); SQLiteDatabase db = DbHelper.getWritableDatabase(); ContentValues cv = new ContentValues(); cv.put(DatabaseHelper.C_MED_NAME, medName); db.insert(DatabaseHelper.TABLE_NAME, DatabaseHelper.C_MED_NAME, cv); db.close(); } } public void refresh(){ cur = db.query("Medicines", null, null, null, null, null, null); ladapter.notifyDataSetChanged(); } 

try this, I think your context is null, so it goes like this

Answer 2

Once you have installed the adapter, you do not need to do .setListAdapter() . Declare the adapter as a global variable in your class (as at the beginning), and then just call adapter.notifyDataSetChanged() at the point where there are changes to the adapter data. If it does not work, try reinstalling the adapter and notifyDataSetChanged() it on, then call notifyDataSetChanged() .

In an attempt to remove the adapter type definition, you already made public SimpleCursorAdapter ladapter; by simply passing it using the data in try.