sqlite select해서 리스트뷰에 보여주려고 합니다. 근데 저런 에러가 뜹니다. 어떻게 해야되요???
DBHelper.java
public class DBHelper extends SQLiteOpenHelper {
public static final int DATABASE_VERSION = 1;
private Context context;
public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory, DATABASE_VERSION);
this.context = context;
// createDB();
Log.d("1","1");
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.d("2","2");
StringBuffer sb=new StringBuffer();
sb.append(" CREATE TABLE MEMO ( ");
sb.append(" _id INTEGER PRIMARY KEY AUTOINCREMENT, ");
sb.append(" title TEXT, ");
sb.append(" content TEXT ) ");
db.execSQL(sb.toString());
// db.execSQL("CREATE TABLE MEMO(_id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, content TEXT);");
Log.d("DBHelper", "테이블 생성");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.d("3","3");
}
public void insert(MemoData memoData) {
Log.d("4","4");
SQLiteDatabase db = this.getWritableDatabase();
StringBuffer sb=new StringBuffer();
sb.append("insert into MEMO(");
sb.append("title,content)");
sb.append("values(?,?);");
db.execSQL(sb.toString(), new Object[]{
memoData.getTitle(),
memoData.getContent()});
Log.d("Insert","완료");
}
public void update(String title, String content) {
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL("UPDATE MEMO SET title=" + title + "," + "content=" + content + "WHERE title='" + title + "';");
db.close();
Log.d("5","5");
}
public void delete(String title) {
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL("DELETE FROM MEMO WHERE title='" + title + "';");
db.close();
Log.d("6","6");
}
public String select(int index){
SQLiteDatabase db = this.getReadableDatabase();
StringBuffer sb=new StringBuffer();
String result="";
Cursor cursor=db.rawQuery("SELECT title FROM MEMO where _id"+index,null);
while (cursor.moveToNext()){
result+=cursor.getString(0);
}
Log.d("7","7");
return result;
}
public void testDB(){
Log.d("8","8");
SQLiteDatabase db=getReadableDatabase();
Log.d("dddd","dddd");
}
}
MainActivity.java
public class MainActivity extends AppCompatActivity{
private DBHelper dbHelper;
MemoListAdapter adapter;
ListView lv;
InputMethodManager imm;
ImageButton reflesh;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
reflesh=(ImageButton)findViewById(R.id.reflesh);
Log.d("메인","화면");
imm=(InputMethodManager)getSystemService(INPUT_METHOD_SERVICE);
findViewById(R.id.addmemo).setOnClickListener(clickListener);
reflesh.setOnClickListener(refleshonClick);
}
View.OnClickListener refleshonClick=new View.OnClickListener() {
@Override
public void onClick(View v) {
try{
adapter=new MemoListAdapter();
lv=(ListView)findViewById(R.id.memoListView);
lv.setAdapter(adapter);
while (true){
int i=1;
String title=dbHelper.select(i);
adapter.addItem(title,String.valueOf(new Date(System.currentTimeMillis())));
adapter.notifyDataSetChanged();
i++;
Log.d("리스트","추가");
}
}catch (Exception e){
e.printStackTrace();
}
}
};
}MemoListAdapter.java
public class MemoListAdapter extends BaseAdapter implements View.OnClickListener {
private ArrayList<ListViewItem> listViewItemList = new ArrayList<ListViewItem>();
public MemoListAdapter() {
}
@Override
public int getCount() {
return listViewItemList.size();
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public void onClick(View v) {
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
final int pos = position;
final Context context = parent.getContext();
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.listview_item, parent, false);
}
TextView titleTextView = (TextView) convertView.findViewById(R.id.title);
TextView dateTextView = (TextView) convertView.findViewById(R.id.date);
Button button = (Button) convertView.findViewById(R.id.delete);
button.setText("삭제");
button.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
listViewItemList.remove(pos);
notifyDataSetChanged();
}
});
ListViewItem listViewItem = listViewItemList.get(position);
titleTextView.setText(listViewItem.getTitle());
dateTextView.setText(listViewItem.getDate());
return convertView;
}
@Override
public Object getItem(int position) {
return listViewItemList.get(position);
}
public void addItem(String title, String date) {
ListViewItem item = new ListViewItem();
item.setTitleStr(title);
item.setDateStr(date);
listViewItemList.add(item);
}
}에러
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.dsm2016.memo.DBHelper.select(int)' on a null object reference
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at com.example.dsm2016.memo.MainActivity$1.onClick(MainActivity.java:54)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at android.view.View.performClick(View.java:5198)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at android.view.View$PerformClick.run(View.java:21147)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at android.os.Handler.handleCallback(Handler.java:739)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at android.os.Handler.dispatchMessage(Handler.java:95)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at android.os.Looper.loop(Looper.java:148)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at android.app.ActivityThread.main(ActivityThread.java:5417)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at java.lang.reflect.Method.invoke(Native Method)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
08-01 05:29:52.732 26228-26228/com.example.dsm2016.memo W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
