当我想使用游标从SQLite数据库中获取数据时，找到的数据集的数量是正确的，但输出是错误的（或者至少不是我需要它的方式）：它看起来像这样：< / p>
com.example.plabsprojects.mtgcommanderlifecounter.DB_Memo@eb38ae1
我在数据库中有三个不同的表。有人告诉我要覆盖toString()
@Override
public String toString(){
String output = "ID: " + id_actions + ", Name: " + action_name;
return output;
}
问题是，我需要在这个String中调用不同的变量而不知道如何。一般方法改编自教程。但他们没有解释，为什么他们会覆盖toString()
我该如何解决这个问题？
这听起来有点令人困惑......我还在学习:)。
我使用三个类：DB_Memo，DB_DataSource和DB_Helper。代码如下：）
DB_MEMO：
public class DB_Memo {
//Variables for Table Player
private long id_player;
private String player_name;
//Variables for Table Actions
private long id_actions;
private String action_name;
private int action_points;
//Variables for Table Tracking
private long id_tracking;
private long id_player_tracking;
private long id_actions_tracking;
private long match_id;
private String created_at;
public DB_Memo(long id_player, String player_name){
this.id_player = id_player;
this.player_name = player_name;
}
public DB_Memo(long id_actions, String action_name, int action_points){
this.id_actions = id_actions;
this.action_name = action_name;
this.action_points = action_points;
}
public DB_Memo(long id_tracking, long id_player_tracking, long id_actions_tracking, long match_id, String created_at){
this.id_tracking = id_tracking;
this.id_player_tracking = id_player_tracking;
this.id_actions_tracking = id_actions_tracking;
this.match_id = match_id;
this.created_at = created_at;
}
//Setter
public void setId_player(){
this.id_player = id_player;
}
public void setPlayer_name(){
this.player_name = player_name;
}
public void setId_actions(){
this.id_actions = id_actions;
}
public void setAction_name(){
this.action_name = action_name;
}
public void setAction_points(){
this.action_points = action_points;
}
public void setId_tracking(){
this.id_tracking = id_tracking;
}
public void setId_player_tracking(){
this.id_player_tracking = id_player_tracking;
}
public void setId_actions_tracking(){
this.id_actions_tracking = id_actions_tracking;
}
public void setMatch_id(){
this.match_id = match_id;
}
public void setCreated_at(){
this.created_at = created_at;
}
//Getter
public long getId_player(){return id_player;}
public String getPlayer_name(){return player_name;}
public long getId_actions(){return id_actions;}
public String getAction_name(){return action_name;}
public int getAction_points(){return action_points;}
public long getId_tracking(){return id_tracking;}
public long getId_player_tracking(){return id_player_tracking;}
public long getId_actions_tracking(){return id_actions_tracking;}
public long getMatch_id(){return match_id;}
public String getCreated_at(){return created_at;}
// @Override
// public String toString(){
// String output = "ID: " + id_actions + ", Name: " + action_name;
// return output;
// }
}
DB_DataSource：
public class DB_DataSource {
private static final String LOG_TAG = DB_DataSource.class.getSimpleName();
private SQLiteDatabase database;
private DB_Helper db_helper;
private String[] columns_player = {
DB_Helper.COLUMN_ID_PLAYER,
DB_Helper.COLUMN_PLAYER_NAME
};
private String[] columns_actions = {
DB_Helper.COLUMN_ID_ACTIONS,
DB_Helper.COLUMN_ACTION_NAME,
DB_Helper.COLUMN_ACTION_POINTS,
};
private String[] columns_tracking = {
DB_Helper.COLUMN_ID_TRACKING,
DB_Helper.COLUMN_TRACKING_PLAYER_ID,
DB_Helper.COLUMN_TRACKING_ACTION_ID,
DB_Helper.COLUMN_TRACKING_MATCH_ID,
DB_Helper.COLUMN_TIMESTAMP,
};
public DB_DataSource(Context context){
Log.d(LOG_TAG, "DataSource erzeugt jetzt den DB_Helper.");
db_helper = new DB_Helper(context );
}
public void open(){
Log.d(LOG_TAG, "Eine Referenz auf die Datenbank wird jetzt angefragt.");
database = db_helper.getWritableDatabase();
Log.d(LOG_TAG, "Datenbank-Referenz erhalten. Pfad zur Datenbank." + database.getPath());
}
public void close(){
db_helper.close();
Log.d(LOG_TAG, "Datenbank mithilfe des DBhelpers geschlossen.");
}
public DB_Memo createPlayer(String player_name){
ContentValues values = new ContentValues();
values.put(DB_Helper.COLUMN_PLAYER_NAME, player_name);
long insertID = database.insert(DB_Helper.TABLE_PLAYER_NAMES, null, values);
Cursor cursor = database.query(DB_Helper.TABLE_PLAYER_NAMES, columns_player, DB_Helper.COLUMN_ID_PLAYER + "=" + insertID,
null, null, null, null);
cursor.moveToFirst();
DB_Memo db_memo = cursorToDB_Memo(cursor, 1);
cursor.close();
return db_memo;
}
public DB_Memo createAction(String action_name, int action_points){
ContentValues values = new ContentValues();
values.put(DB_Helper.COLUMN_ACTION_NAME, action_name);
values.put(DB_Helper.COLUMN_ACTION_POINTS, action_points);
long insertID = database.insert(DB_Helper.TABLE_ACTIONS, null, values);
Cursor cursor = database.query(DB_Helper.TABLE_ACTIONS, columns_actions, DB_Helper.COLUMN_ID_ACTIONS + "=" + insertID,
null, null, null, null);
cursor.moveToFirst();
DB_Memo db_memo = cursorToDB_Memo(cursor, 2);
cursor.close();
return db_memo;
}
private DB_Memo cursorToDB_Memo(Cursor cursor, int table){
if(table==1) {
int idIndex = cursor.getColumnIndex(DB_Helper.COLUMN_ID_PLAYER);
int idPlayer_name = cursor.getColumnIndex(DB_Helper.COLUMN_PLAYER_NAME);
String player_name = cursor.getString(idPlayer_name);
long id = cursor.getLong(idIndex);
DB_Memo db_memo = new DB_Memo(id, player_name);
return db_memo;
}
else if (table == 2){
int idIndex = cursor.getColumnIndex(DB_Helper.COLUMN_ID_ACTIONS);
int idaction_name = cursor.getColumnIndex(DB_Helper.COLUMN_ACTION_NAME);
int idaction_points = cursor.getColumnIndex(DB_Helper.COLUMN_ACTION_POINTS);
String action_name = cursor.getString(idaction_name);
long id = cursor.getLong(idIndex);
DB_Memo db_memo = new DB_Memo(id, action_name, idaction_points);
return db_memo;
}
else {
int idIndex = cursor.getColumnIndex(DB_Helper.COLUMN_ID_PLAYER);
int idPlayer_name = cursor.getColumnIndex(DB_Helper.COLUMN_PLAYER_NAME);
String player_name = cursor.getString(idPlayer_name);
long id = cursor.getLong(idIndex);
DB_Memo db_memo = new DB_Memo(id, player_name);
return db_memo;
}
}
public List<DB_Memo> getAllPlayerNames(){
List<DB_Memo> db_memoList = new ArrayList<>();
Cursor cursor = database.query(DB_Helper.TABLE_PLAYER_NAMES, columns_player,
null, null, null, null, null);
cursor.moveToFirst();
DB_Memo db_memo;
while(!cursor.isAfterLast()){
db_memo = cursorToDB_Memo(cursor ,1);
db_memoList.add(db_memo);
cursor.moveToNext();
}
cursor.close();
return db_memoList;
}
public List<DB_Memo> getAllActions(){
List<DB_Memo> db_memoList = new ArrayList<>();
Cursor cursor = database.query(DB_Helper.TABLE_ACTIONS, columns_actions,
null, null, null, null, null);
cursor.moveToFirst();
DB_Memo db_memo;
while(!cursor.isAfterLast()){
db_memo = cursorToDB_Memo(cursor, 2);
db_memoList.add(db_memo);
cursor.moveToNext();
}
cursor.close();
return db_memoList;
}
}
DB_Helper：
public class DB_Helper extends SQLiteOpenHelper {
public static final String DB_NAME = "mtg_league.db";
public static final int DB_VERSION = 1;
//TABLE PLAYER
public static final String TABLE_PLAYER_NAMES = "table_player";
public static final String COLUMN_ID_PLAYER = "_id";
public static final String COLUMN_PLAYER_NAME = "player_name";
public static final String SQL_CREATE_PLAYER =
"CREATE TABLE " + TABLE_PLAYER_NAMES +
"(" + COLUMN_ID_PLAYER + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COLUMN_PLAYER_NAME + " TEXT NOT NULL);";
//TABLE ACTIONS
public static final String TABLE_ACTIONS = "table_actions";
public static final String COLUMN_ID_ACTIONS = "_id";
public static final String COLUMN_ACTION_NAME = "action_name";
public static final String COLUMN_ACTION_POINTS = "action_points";
public static final String SQL_CREATE_ACTIONS =
"CREATE TABLE " + TABLE_ACTIONS +
"(" + COLUMN_ID_ACTIONS + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COLUMN_ACTION_NAME + " TEXT NOT NULL, " +
COLUMN_ACTION_POINTS + " INTEGER NOT NULL);";
//TABLE TRACKING
public static final String TABLE_TRACKING = "table_tracking";
public static final String COLUMN_ID_TRACKING = "_id";
public static final String COLUMN_TRACKING_PLAYER_ID = "player_id";
public static final String COLUMN_TRACKING_AGAINST_PLAYER_ID = "against_player_id";
public static final String COLUMN_TRACKING_ACTION_ID = "action_id";
public static final String COLUMN_TRACKING_MATCH_ID = "match_id";
public static final String COLUMN_TIMESTAMP = "timestamp";
public static final String SQL_CREATE_TRACKING =
"CREATE TABLE " + TABLE_TRACKING +
"(" + COLUMN_ID_TRACKING + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COLUMN_TRACKING_PLAYER_ID + " TEXT NOT NULL, " +
COLUMN_TRACKING_AGAINST_PLAYER_ID + " TEXT, " +
COLUMN_TRACKING_ACTION_ID + " TEXT NOT NULL, " +
COLUMN_TRACKING_MATCH_ID + " INTEGER NOT NULL, " +
COLUMN_TIMESTAMP + " DATETIME DEFAULT CURRENT_TIMESTAMP);";
public DB_Helper(Context context){
super(context, DB_NAME, null, DB_VERSION);
Log.d("Test", "DB Helper hat die Datenbank: " + getDatabaseName() + " erzeugt.");
}
@Override
public void onCreate(SQLiteDatabase db) {
try{
Log.d("Test", "Tabelle wird mit SQL-Befehl " + SQL_CREATE_PLAYER + " angelegt.");
db.execSQL(SQL_CREATE_PLAYER);
Log.d("Test", "Tabelle wird mit SQL-Befehl " + SQL_CREATE_ACTIONS + " angelegt.");
db.execSQL(SQL_CREATE_ACTIONS);
Log.d("Test", "Tabelle wird mit SQL-Befehl " + SQL_CREATE_TRACKING + " angelegt.");
db.execSQL(SQL_CREATE_TRACKING);
}
catch (Exception ex){
Log.e("Test", "Fehler beim Anlegen der Tabelle: " + ex.getMessage());
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
答案 0 :(得分：1)
<强> com.example.plabsprojects.mtgcommanderlifecounter.DB_Memo@eb38ae1
对象的（DB_Memo实例）是否为默认 toString 方法。
你应该做的是使用对象的适当的getter方法。例如如果您想 id_actions ，那么您将使用类似
的内容 String.valueOf(your_memo_instance.getId_actions());
而不是
your_memo_instance.toString();