Я получаю исключение NullPointerException в строке:
viewHolder.list_item_TextView = convertView.findViewById(R.id.listItem_TextView);
То же приложение работает без проблем, если viewholder не реализовано.Я добавляю viewHolder, как я делал раньше в других приложениях, и они работают.Не могу найти ошибку.
public class lv_cb_db_ea_Adapter extends BaseAdapter {
final private Context context;
private Cursor cursor;
private SQLiteDatabase database;
lv_cb_db_ea_Adapter(Context context, Cursor cursor, SQLiteDatabase database) {
super();
this.context = context;
this.cursor = cursor;
this.database = database;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder;
if (convertView == null) {
LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = layoutInflater.inflate(R.layout.list_item, parent, false);
viewHolder = (ViewHolder) convertView.getTag();
// ######## here comes the NPE #########
viewHolder.list_item_TextView = convertView.findViewById(R.id.listItem_TextView);
viewHolder.list_item_Checkbox = convertView.findViewById(R.id.listItem_CheckBox);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
cursor.moveToPosition(position);
viewHolder.list_item_TextView.setText("Some Text");
viewHolder.list_item_Checkbox.setChecked(cursor.getInt(cursor.getColumnIndex("selected")) != 0);
return convertView;
}
public int getCount() {
return cursor.getCount();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
private static class ViewHolder {
CheckBox list_item_Checkbox;
TextView list_item_TextView;
}
}
вот xml-файл
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<CheckBox
android:id="@+id/listItem_CheckBox"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:focusable="false"
android:focusableInTouchMode="false" />
<TextView
android:id="@+id/listItem_TextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="@+id/listItem_CheckBox" />
</RelativeLayout>
вот логкат:
java.lang.NullPointerException: Attempt to write to field 'android.widget.TextView ws.rtin.android.listviewexample.lv_cb_db_ea_Adapter$ViewHolder.list_item_TextView' on a null object reference
--- добавлен database.javaи listview.java ----
Поскольку есть некоторые ответы (спасибо за это), которые не решают проблему, я выкладываю все свое приложение (только три небольших java-файла и xml).«lv_cb_db_ea» - это основной файл в манифесте.
Вот моя база данных.java
public class database extends SQLiteOpenHelper {
database(Context context) {
super(context, "database", null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE country(" +
"_id integer primary key autoincrement, " +
"code varchar(3) not null," +
"name varchar(30) not null," +
"selected integer not null)"
);
db.execSQL("INSERT INTO country VALUES('0','DK','Dänemark',0)");
db.execSQL("INSERT INTO country VALUES('1','F','Frankreich',1)");
db.execSQL("INSERT INTO country VALUES('2','B','Belgien',0)");
db.execSQL("INSERT INTO country VALUES('3','NL','Niederlande',1)");
db.execSQL("INSERT INTO country VALUES('4','D','Deutschland',0)");
db.execSQL("INSERT INTO country VALUES('6','TR','Türkei',0)");
db.execSQL("INSERT INTO country VALUES('8','S','Schweden',0)");
db.execSQL("INSERT INTO country VALUES('10','FN','Finnland',0)");
db.execSQL("INSERT INTO country VALUES('11','GR','Griechenland',0)");
db.execSQL("INSERT INTO country VALUES('12','A','Östereich',0)");
db.execSQL("INSERT INTO country VALUES('13','LIT','Litauen',0)");
db.execSQL("INSERT INTO country VALUES('14','PL','Polen',0)");
db.execSQL("INSERT INTO country VALUES('15','P','Portugal',0)");
db.execSQL("INSERT INTO country VALUES('16','I','Italien',0)");
db.execSQL("INSERT INTO country VALUES('17','GB','Groß Britannien',0)");
db.execSQL("INSERT INTO country VALUES('18','IRL','Irland',0)");
db.execSQL("INSERT INTO country VALUES('19','L','Luxemburg',0)");
db.execSQL("INSERT INTO country VALUES('20','E','Spanien',0)");
db.execSQL("INSERT INTO country VALUES('21','CH','Schweiz',0)");
db.execSQL("INSERT INTO country VALUES('22','CZ','Tschechien',0)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
, а вот listView («MainActivity»)
public class lv_cb_db_ea extends Activity {
private static SQLiteDatabase sqLiteDatabase;
private Cursor cursor;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// connect to database
SQLiteOpenHelper database = new database(this);
sqLiteDatabase = database.getWritableDatabase();
cursor = getDBContent();
//create an ArrayAdapter by given database-cursor
lv_cb_db_ea_Adapter itemAdapter = new lv_cb_db_ea_Adapter(this, cursor, sqLiteDatabase);
ListView listView = findViewById(R.id.main_ListView);
listView.setAdapter(itemAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
String sToast = ((TextView) view.findViewById(R.id.listItem_TextView)).getText().toString();
Toast.makeText(lv_cb_db_ea.this,
"Clicked on Row: " + sToast,
Toast.LENGTH_SHORT).show();
}
});
}
public void findSelected(View v) {
StringBuilder sToast = new StringBuilder();
sToast.append("You've selected...\n");
cursor = sqLiteDatabase.rawQuery("SELECT * FROM country WHERE selected", null);
while (cursor.moveToNext()) {
sToast.append("\n").append(cursor.getString(cursor.getColumnIndex("name")));
}
Toast.makeText(getApplicationContext(), sToast, Toast.LENGTH_LONG).show();
cursor.close();
}
// outsourcing query (for more complex queries (i.e. multiple tables))
public static Cursor getDBContent(){
return sqLiteDatabase.rawQuery("SELECT * FROM country", null);
}