Im getting a ‘NullPointerException’ when I try and load my intent to a class that handles my listview of the data from my database. I’m a total newbie when it comes to listviews so hopefully someone can tell me where Ive gone wrong!
I was thinking that the null pointer was due to the fact no data was being found at the first row posistion that the cursor is at, but I think looking at the logcat, its an issue with my XML layout ‘entries’?
Heres my class for the ListView:
package com.example.sqliteexample;
import android.app.Activity;
import android.app.ListActivity;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.widget.ListView;
public class SQLView extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
HotOrNot H = new HotOrNot(this, null, null);
setContentView(R.layout.layout);
ListView listContent = (ListView)findViewById(R.id.contentList);
HotOrNot Content = new HotOrNot(this, null, null);
Cursor cursor = Content.getData();
startManagingCursor(cursor);
@SuppressWarnings("static-access")
String [] from = new String [] {H.KEY_NAME, H.KEY_HOTNESS};
int [] to = new int [] {R.id.txtName, R.id.txtAge};
@SuppressWarnings("deprecation")
SimpleCursorAdapter cursorAdapter = new SimpleCursorAdapter(this, R.layout.entries, cursor, from, to);
listContent.setAdapter(cursorAdapter);
The ‘getData’ method from my DB handler class:
public Cursor getData() {
String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
return c;
HotOrNot DB handler class:
package com.example.sqliteexample;
import android.app.ListActivity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.ListView;
public class HotOrNot {
public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "persons_name";
public static final String KEY_HOTNESS = "persons_hotness";
private static String DATABASE_NAME = "HotOrNotdb";
private static String DATABASE_TABLE = "peopleTable";
private static int DATABASE_VERSION = 30;
private static DBHelper ourHelper;
private static Context ourContext;
private static SQLiteDatabase ourDatabase;
ListView listview;
public void DB_NAME(String DBName)
{
DATABASE_NAME = DBName;
}
public String returnDB_NAME()
{
return DATABASE_NAME;
}
public void DB_tableNAME(String DBtName)
{
DATABASE_TABLE = DBtName;
}
public String returnDB_tNAME()
{
return DATABASE_TABLE;
}
public void DB_NAME(int DBVersion)
{
DATABASE_VERSION = DBVersion;
}
public int returnDB_VERSION()
{
return DATABASE_VERSION;
}
// class constructor for context. when the object is constructed in the main programme
// the context of that class i.e 'this' is sent to this constructor to set the object context.
// null values set on SQLiteDatabase and DBhelper as there is nothing to pass from the called
// objects.
public HotOrNot (Context c, SQLiteDatabase newSQL, DBHelper BD)
{
ourContext = c;
ourDatabase = newSQL;
ourHelper = BD;
}
private static class DBHelper extends SQLiteOpenHelper
{
public DBHelper(Context context) {
super(context, KEY_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" +
KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
KEY_NAME + " TEXT NOT NULL, " +
KEY_HOTNESS + " TEXT NOT NULL);"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
}
public HotOrNot open() throws SQLException
{
ourHelper = new DBHelper(ourContext);
ourDatabase = ourHelper.getWritableDatabase();
return this;
}
public void close()
{
ourHelper.close();
}
public long createEntry(String name, String hotness) {
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, name);
cv.put(KEY_HOTNESS, hotness);
return ourDatabase.insert(DATABASE_TABLE, null, cv);
}
public Cursor getData() {
String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
//String result = "";
//int iRow = c.getColumnIndex(KEY_ROWID);
//int iName = c.getColumnIndex(KEY_NAME);
//int ihotness = c.getColumnIndex(KEY_HOTNESS);
//for(c.moveToFirst(); !c.isAfterLast(); c.moveToNext())
//{
//result = result + c.getString(iRow) + "" + c.getString(iName) + "" + c.getString(ihotness);
//}
//c.close();
return c;
}
public String getName(long l) {
String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "=" + l, null, null, null, null);
if(c != null)
{
// move to the selected row
c.moveToFirst();
String name = c.getString(1);
return name;
}
return null;
}
public String getHotness(long l) {
String [] columns = new String[]{KEY_ROWID, KEY_NAME, KEY_HOTNESS};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "=" + l, null, null, null, null);
if(c != null)
{
// move to the selected row
c.moveToFirst();
String hotness = c.getString(2);
return hotness;
}
return null;
}
public void updateEntry(long newl, String nameEdit, String hotnessEdit) {
ContentValues cvUpdate = new ContentValues();
cvUpdate.put(KEY_NAME, nameEdit);
cvUpdate.put(KEY_HOTNESS, hotnessEdit);
ourDatabase.update(DATABASE_TABLE, cvUpdate, KEY_ROWID + "=" + newl, null);
}
public void delID(long l) {
ourDatabase.delete(DATABASE_TABLE, KEY_ROWID + "=" + l, null);
}
}
My XML layout for the listview:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/txtName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Name:" />
<TextView
android:id="@+id/txtAge"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Age:" />
</LinearLayout>
The listview XML layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ListView
android:id="@+id/contentList"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
</ListView>
</LinearLayout>
Logcat:
01-11 00:23:26.655: D/AndroidRuntime(272): Shutting down VM
01-11 00:23:26.655: W/dalvikvm(272): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
01-11 00:23:26.675: E/AndroidRuntime(272): FATAL EXCEPTION: main
01-11 00:23:26.675: E/AndroidRuntime(272): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sqliteexample/com.example.sqliteexample.SQLView}: java.lang.NullPointerException
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.os.Handler.dispatchMessage(Handler.java:99)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.os.Looper.loop(Looper.java:123)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.ActivityThread.main(ActivityThread.java:4627)
01-11 00:23:26.675: E/AndroidRuntime(272): at java.lang.reflect.Method.invokeNative(Native Method)
01-11 00:23:26.675: E/AndroidRuntime(272): at java.lang.reflect.Method.invoke(Method.java:521)
01-11 00:23:26.675: E/AndroidRuntime(272): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-11 00:23:26.675: E/AndroidRuntime(272): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-11 00:23:26.675: E/AndroidRuntime(272): at dalvik.system.NativeStart.main(Native Method)
01-11 00:23:26.675: E/AndroidRuntime(272): Caused by: java.lang.NullPointerException
01-11 00:23:26.675: E/AndroidRuntime(272): at com.example.sqliteexample.HotOrNot.getData(HotOrNot.java:143)
01-11 00:23:26.675: E/AndroidRuntime(272): at com.example.sqliteexample.SQLView.onCreate(SQLView.java:24)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-11 00:23:26.675: E/AndroidRuntime(272): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
You simply forgot to call
open().(But please read about Java naming conventions, which state variables should start with a lowercase letter.)