我想从SQLite数据库中填充的值列表中删除一个项目。但我似乎无法让它发挥作用。 MySQLiteperper类具有SQL操作，ListViewDelete具有onlistItemClick，其中基于他选择的项目（代表一个位置），该记录应该从SQLite数据库中删除。
--- MySQLitehelper.java ----
public class MySQLitehelper {
//public static final String TABLE_COMMENTS = "comments";
public static final String COLUMN_ID = "GWid";
public static final String COLUMN_DATE = "DateGWU";
public static final String COLUMN_LOCATION = "location";
public static final String COLUMN_TIME = "time";
public static final String TABLE_NAME = "UPDTable";
private static final String DATABASE_NAME = "UPDdb_version6";
private static final int DATABASE_VERSION = 6;
private final Context context;
GetSet getset = new GetSet();
public void GetIdForGwid(GetSet get)
{
getset=get;
}
// Database creation sql statement
private static final String DATABASE_CREATE = "CREATE TABLE " + TABLE_NAME +
" (" +COLUMN_ID+ " integer," + COLUMN_DATE + " VARCHAR," +
COLUMN_LOCATION+" VARCHAR," +COLUMN_TIME +" VARCHAR);";
// private static final String DATABASE_INSERT = "INSERT INTO " +TABLE_NAME +
// " Values (47688507,'DEC-07-2012','MARVIN 203','20:00');";
private static final String DATABASE_INSERT = "INSERT INTO " +TABLE_NAME + " (" +COLUMN_ID+ " ," + COLUMN_DATE + "," +
COLUMN_LOCATION+" ," +COLUMN_TIME +" )" +
" Values (47688507,'DEC-07-2012','MARVIN 203','20:00');";
DatabaseHelper dbhelper;
SQLiteDatabase db;
public MySQLitehelper(Context ctx)
{
this.context = ctx;
dbhelper = new DatabaseHelper(ctx);
}
private static class DatabaseHelper extends SQLiteOpenHelper {
public DatabaseHelper(Context context)
{
super(context,DATABASE_NAME, null,DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(DATABASE_CREATE); //execute create table
db.execSQL(DATABASE_INSERT); //execute insert query
db.execSQL("INSERT INTO " +TABLE_NAME + " (" +COLUMN_ID+ " ," + COLUMN_DATE + "," +COLUMN_LOCATION+" ," +COLUMN_TIME +" )" +" Values (47688507,'DEC-22-2012','OLD MAIN','23:00');");
db.execSQL("INSERT INTO " +TABLE_NAME + " (" +COLUMN_ID+ " ," + COLUMN_DATE + "," +COLUMN_LOCATION+" ," +COLUMN_TIME +" )" +" Values (1234567,'DEC-14-2012','FUNGER','12:00');");
db.execSQL("INSERT INTO " +TABLE_NAME + " (" +COLUMN_ID+ " ," + COLUMN_DATE + "," +COLUMN_LOCATION+" ," +COLUMN_TIME +" )" +" Values (7654321,'DEC-29-2012','GELMAN','22:00');");
db.execSQL("INSERT INTO " +TABLE_NAME + " (" +COLUMN_ID+ " ," + COLUMN_DATE + "," +COLUMN_LOCATION+" ," +COLUMN_TIME +" )" +" Values (47688507,'DEC-12-2012','IVORY','23:00');");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
Log.w(MySQLitehelper.class.getName(),
"Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
// open the DB
public MySQLitehelper open() throws SQLException
{
System.out.println("Inside open function");
db = dbhelper.getWritableDatabase();
return this;
}
public void close()
{
dbhelper.close();
}
public void insertRecord(long gwid, String date, String location, String time)
{
ContentValues initialValues = new ContentValues();
initialValues.put(COLUMN_ID, gwid);
initialValues.put(COLUMN_DATE, date);
initialValues.put(COLUMN_LOCATION, location);
initialValues.put(COLUMN_TIME, time);
db.insert(TABLE_NAME, null, initialValues);
}
public Cursor getAllrows() //function to get all rows in the DB. Testing initially.
{
Cursor cur = db.rawQuery("SELECT * FROM "+TABLE_NAME, null);
return cur;
}
public Cursor getRecord(long getid) throws SQLException
{
Cursor mCursor =
db.query(true, TABLE_NAME, new String[] {COLUMN_ID,
COLUMN_DATE, COLUMN_LOCATION, COLUMN_TIME},
COLUMN_ID + "= "+getid, null, null, null, null, null);
if (mCursor != null)
{
mCursor.moveToFirst();
}
return mCursor;
}
public void DeleteRecord (String location)
{
try {
//String sSQLQuery = "DELETE FROM "+TABLE_NAME +
// "WHERE "+COLUMN_LOCATION+"='" + location + "';";
//db.execSQL(sSQLQuery);
//db.dele
this.db.delete(
TABLE_NAME,
COLUMN_LOCATION+" = "+location,null);
String Message = "Record is deleted: ";
} catch (SQLiteException ex) {
}
}
}
- ListViewDelete.java ---其中onItemListClick方法
public class ListViewDelete extends ListActivity {
private ArrayList<String> thelist;
final MySQLitehelper dbhelper = new MySQLitehelper(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_list_view_delete);
final Intent intent = getIntent();
final Bundle extras = getIntent().getExtras(); //gets the GWID
thelist = new ArrayList<String>(extras.getStringArrayList(SelectOptions.EXTRA_MESSAGE));
setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,extras.getStringArrayList(SelectOptions.EXTRA_MESSAGE)));
}
public void onListItemClick(ListView parent, View view, int position, long id)
{
Toast.makeText(this, "You have selected "+thelist.get(position)+" and will be deleted", Toast.LENGTH_LONG).show();
thelist.remove(position);
dbhelper.DeleteRecord(thelist.get(position)); // I don't know how to deal with this statement
}
}
LOGCAT输出
12-03 19:40:04.959: W/dalvikvm(6510): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
12-03 19:40:04.998: E/AndroidRuntime(6510): FATAL EXCEPTION: main
12-03 19:40:04.998: E/AndroidRuntime(6510): java.lang.NullPointerException
12-03 19:40:04.998: E/AndroidRuntime(6510): at com.example.upd.MySQLitehelper.DeleteRecord(MySQLitehelper.java:147)
12-03 19:40:04.998: E/AndroidRuntime(6510): at com.example.upd.ListViewDelete.onListItemClick(ListViewDelete.java:45)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.app.ListActivity$2.onItemClick(ListActivity.java:319)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.widget.AdapterView.performItemClick(AdapterView.java:298)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.widget.AbsListView.performItemClick(AbsListView.java:1100)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2749)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.widget.AbsListView$1.run(AbsListView.java:3423)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.os.Handler.handleCallback(Handler.java:725)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.os.Handler.dispatchMessage(Handler.java:92)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.os.Looper.loop(Looper.java:137)
12-03 19:40:04.998: E/AndroidRuntime(6510): at android.app.ActivityThread.main(ActivityThread.java:5039)
12-03 19:40:04.998: E/AndroidRuntime(6510): at java.lang.reflect.Method.invokeNative(Native Method)
12-03 19:40:04.998: E/AndroidRuntime(6510): at java.lang.reflect.Method.invoke(Method.java:511)
12-03 19:40:04.998: E/AndroidRuntime(6510): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-03 19:40:04.998: E/AndroidRuntime(6510): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-03 19:40:04.998: E/AndroidRuntime(6510): at dalvik.system.NativeStart.main(Native Method)
12-03 19:40:09.049: I/Process(6510): Sending signal. PID: 6510 SIG: 9
这是我陷入项目的最后一部分。
答案 0 :(得分：3)
但我似乎没有让它发挥作用。
首先，不要将MySQLitehelper类作为ListActivity中的字段进行实例化，而是在onCreate方法中进行：
// ...
final MySQLitehelper dbhelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_list_view_delete);
dbHelper = new MySQLitehelper(this);
// ...
您也忘了在open实例上调用MySQLitehelper方法，否则，如果没有此调用，SQLiteDatabase类中的MySQLitehelper引用为null，它将抛出那NullPointerException：
// ....
thelist.remove(position);
try {
dbhelper.open();
} catch (SQLException sqle) {
Log.e("TAG", "Never ignore exception!!! " + sqle);
}
dbhelper.DeleteRecord(thelist.get(position));
答案 1 :(得分：0)
ArrayAdapter ad =new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,extras.getStringArrayList(SelectOptions.EXTRA_MESSAGE));
public void onListItemClick(ListView parent, View view, int position, long id)
{
Toast.makeText(this, "You have selected "+thelist.get(position)+" and will be deleted", Toast.LENGTH_LONG).show();
thelist.remove(position);
dbhelper.DeleteRecord(thelist.get(position)); // I don't know how to deal with this statement
ad.notifyDataSetChanged(); <------ TRY THIS
}