Question

早上好，我有问题。

所以我想从下面的方法返回一个多值是我的代码：

public static String getReferee(String referee_id, SQLiteDatabase sqLiteDatabase)
{
    Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM tbl_referee", null);
    String refereeInfo = null;
    if (cursor != null)
    {
        if (cursor.moveToFirst())
        {
            do
            {
                String nameInRecord = cursor.getString(1);

                if (nameInRecord.equals(referee_id))
                {
                    String referee_name = cursor.getString(0);        // 0 means table column of REFEREE NAME
                    String referee_game1 = cursor.getString(2);       // 2 means table column of REFEREE GAME 1
                    String referee_game2 = cursor.getString(3);       // 3 means table column of REFEREE GAME 2
                    refereeInfo = referee_name + referee_game1 + referee_game2;
                    break;
                }
            }
            while (cursor.moveToNext());
        }
    }
    return refereeInfo1,refereeInfo2,refereeInfo3,refereeInfo4;
}

如您所见，返回码仅返回字符串RefereeInfo，其中包含来自我的查询的多个数据。如何返回多个String并将其传递给我的Main Activity。

下面的代码是我的主要活动：

 //GET REFEREE PROFILE
private void getRefereeProfile()
{
    String memberInfo = SQLiteFunctionUtility.getReferee(referee_id, mDbHelper.getSqliteObjectWithReadable());
    if (memberInfo != null)
    {
        txtview1.setText(returnstatement1);
        txtview2.setText(returnstatement2);
        txtview3.setText(returnstatement3);
        txtview4.setText(returnstatement4);
    }
    else
    {
        Toast.makeText(MainActivity.this, "No Referee Found", Toast.LENGTH_LONG).show();
    }

我从网上搜索所有内容，因此急需答案。预先谢谢您！

Answer 1

为了返回多个值，您需要将它们放入一个对象并返回该对象。您可以使用List或String[]，但为此目的使用自定义类会更加明确：

public static class Referee
{
    private String name;
    private String game1;
    private String game2;

    public Referee(String name, String game1, String game2)
    {
        this.name = name;
        this.game1 = game1;
        this.game2 = game2;
    }

    // Getters...
}

public static Referee getReferee(String referee_id, SQLiteDatabase sqLiteDatabase)
{
    Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM tbl_referee", null);
    String refereeInfo = null;
    if (cursor != null)
    {
        if (cursor.moveToFirst())
        {
            do
            {
                String nameInRecord = cursor.getString(1);

                if (nameInRecord.equals(referee_id))
                {
                    String referee_name = cursor.getString(0);  // 0 means table column of REFEREE NAME
                    String referee_game1 = cursor.getString(2); // 2 means table column of REFEREE GAME 1
                    String referee_game2 = cursor.getString(3); // 3 means table column of REFEREE GAME 2
                    return new Referee(referee_name, referee_game1, referee_game2);
                }
            } while (cursor.moveToNext());
        }
    }
    return null;
}

如果您有一个名为getReferee的方法，则可以很好地表明您还应具有该方法返回的类型Referee。这样，您的代码就变得不言自明了。

您可以在主要活动中使用这种新类型，如下所示：

private void getRefereeProfile()
{
    Referee memberInfo = SQLiteFunctionUtility.getReferee(referee_id, mDbHelper.getSqliteObjectWithReadable());
    if (memberInfo != null)
    {
        txtview1.setText(memberInfo.getName());
        txtview2.setText(memberInfo.getGame1());
        txtview3.setText(memberInfo.getGame2());
        // what is txtView4 for?
    }
    else
    {
        Toast.makeText(MainActivity.this, "No Referee Found", Toast.LENGTH_LONG).show();
    }

Answer 2

您没有提供Java语法。您可以做的是创建一个包装器对象，该对象将保存要返回的所有值，并将其作为一个对象返回。

或者，您可以使用ArrayList或java数组对象。

Answer 3

像这样创建一个定义所有值的pojo类，并为数据库创建方法。

public User getUser(String email, String password) {
    User user = new User();
    SQLiteDatabase db = this.getReadableDatabase();
    String selectQuery = "SELECT  * FROM " + Reg_TABLE_NAME + " WHERE email=" + email + " AND password=" + password;
    Cursor c = db.rawQuery(selectQuery, null);
    if (c != null) {
        c.moveToFirst();
        while (c.isAfterLast() == false) {
            user.email = (c.getInt(c.getColumnIndex("email")));
            user.password = (c.getString(c.getColumnIndex("password")));
            c.moveToNext();
        }
    }
    c.close();
    db.close();
    return user;
}

获取用户数据后，您可以显示电子邮件和密码。

制作一个可以执行所有操作的数据库类。

public class DB extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "myDb";
public static final String Reg_TABLE_NAME = "Register";

public Context mContext;

public DB(Context context) {
    super(context, DATABASE_NAME, null, 1);
    mContext = context;
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("create table " + Reg_TABLE_NAME + " (id integer primary key, email text, password text)");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + Reg_TABLE_NAME);
    onCreate(db);
}

public User insertUser(User user) {
    java.util.Date date = new java.util.Date();
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues = new ContentValues();
    contentValues.put("email", user.getEmail());
    contentValues.put("password", user.getPassword());
    long insertId = db.insert(Reg_TABLE_NAME, null, contentValues);
    db.close();
}

public void deleteComment(int id) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(Reg_TABLE_NAME, "id =" + id, null);
    db.close();
}

public User getUser(String email, String password) {
    User user = new User();
    SQLiteDatabase db = this.getReadableDatabase();
    String selectQuery = "SELECT  * FROM " + Reg_TABLE_NAME + " WHERE email=" + email + " AND password=" + password;
    Cursor c = db.rawQuery(selectQuery, null);
    if (c != null) {
        c.moveToFirst();
        while (c.isAfterLast() == false) {
            user.email = (c.getInt(c.getColumnIndex("email")));
            user.password = (c.getString(c.getColumnIndex("password")));
            c.moveToNext();
        }
    }
    c.close();
    db.close();
    return user;
}
}

然后执行插入，更新，读取，删除等操作，将其插入活动和片段中。

        DB db=new DB(this); // if fragment then pass getActivity()
    User user=new User();
    user.setEmail("sdf");
    user.setPassword("sdf");
    db.insertUser(user);

Answer 4

您不能从Java中的方法返回多个值。没有语法可以像您一样返回多个字符串。您可以使用String Builder，Buffer或Array列表来完成此工作。

如果使用数组列表，请执行以下操作：-

ArrayList<String> arr= new ArrayList<String>();
arr.add(refereeInfo1);
arr.add(refereeInfo2);
arr.add(refereeInfo3);
arr.add(refereeInfo4);

然后您可以将该列表返回为：-

return arr;

还将方法的返回类型从String更改为List。

Answer 5

您可以使用元组-匿名/不相关元素的集合。阅读本文http://www.baeldung.com/java-tuples。 AFAIK Android SDK包含对元组。 Kotlin语言具有成对和三重。如果愿意，可以编写带有N个参数的元组，其中0

从方法返回多个值

5 个答案: