Question

我试图从tableName使用SELECT *来获取Array列表。但我只是以奇怪的方式获得最后一排。我举例说明了我们。我只有两行数据，我手动放置。假设数据分别是StackOverFlow和Google与Ids 1和2。我得到的只是谷歌和谷歌两次。这是我的代码;

在投资组合类中;

    trainingArrayList = new ArrayList<Training>();

    //creates and open the database so we can use it
    DatabaseHelper db = DatabaseHelper.getInstance();

    // Getting a cursor to fetch data from the database
    final Cursor cursor = db.select("SELECT * FROM training");

    if (cursor.moveToFirst()) {

        while (cursor.isAfterLast() == false) {
            Training training = Training.getInstance();
            training.setId(cursor.getInt(cursor
                    .getColumnIndex(DatabaseHelper.TRAINING_ID)));
            training.setTitle(cursor.getString(cursor
                    .getColumnIndex(DatabaseHelper.TRAINING_TITLE)));
            training.setDescription(cursor.getString(cursor
                    .getColumnIndex(DatabaseHelper.TRAINING_DESCRIPTION)));
            training.setDate(cursor.getString(cursor
                    .getColumnIndex(DatabaseHelper.TRAINING_DATE)));
            training.setLocation(cursor.getString(cursor
                    .getColumnIndex(DatabaseHelper.TRAINING_LOCATION)));

            this.trainingArrayList.add(training);
            cursor.moveToNext();
        }
    }

我的培训课程是：

public class Training {

private static Training instance = null;

// global variables
public int id;
public String title;
public String description;
public String date;
public String location;
private Trainer trainer;

private ArrayList<Trainee> traineeArrayList;

private Training(){
    //Restrict the constructor from being instantiated
}

public static Training getInstance(){
    if(instance == null){
        instance = new Training();
    }
    return instance;

}

// Constructor
public Training(int _id, String title, String description, String date,
        String location) {

    this.id = _id;
    this.title = title;
    this.description = description;
    this.date = date;
    this.location = location;
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;

}

public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

public String getDate() {
    return date;
}

public void setDate(String date) {
    this.date = date;
}

public String getLocation() {
    return location;
}

public void setLocation(String location) {
    this.location = location;

}

public Trainer getTrainer() {
    return trainer;
}

public Training (Context context) {

    DatabaseHelper db = DatabaseHelper.getInstance();

    traineeArrayList = new ArrayList<Trainee>();

    Cursor cursor = db.select("SELECT * FROM person p JOIN attendance a ON p.person_id = a.person_id WHERE training_id="+this.getId()+";");

    while (cursor.moveToNext()) {
        Trainee trainee = new Trainee();
        trainee.setID(cursor.getInt(cursor.getColumnIndex(DatabaseHelper.PERSON_ID)));
        trainee.setFirstname(cursor.getString(cursor.getColumnIndex(DatabaseHelper.PERSON_FIRSTNAME)));
        trainee.setLastname(cursor.getString(cursor.getColumnIndex(DatabaseHelper.PERSON_LASTNAME)));
        //TODO

        // Pass to the arraylist
        this.traineeArrayList.add(trainee);
    }
}

/* returns the title of training in training ;ist. 
 * @see java.lang.Object#toString()
 */
@Override
public String toString() {

    return title;
}

我的主要活动课程：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    portfolio = new Portfolio(this);

    trainingListAdapter = new ArrayAdapter<Training>(this,
            android.R.layout.simple_list_item_1,
            portfolio.getTrainingArrayList());

    setListAdapter(trainingListAdapter);

Answer 1

使用

while (cursor.moveToNext()) {
...
}

光标在第一行之前开始。在第一次迭代中，如果存在，则移动到第一个结果。如果光标为空，或者最后一行已经处理，则循环退出

Answer 2

使用：

 // move the cursor pointer to position zero.
        cursor.moveToFirst();

            // if there is data after the current cursor position, add it
            // to the ArrayList.
            if (!cursor.isAfterLast())
            {
                do
                {
        // get `training` data          
        trainingArrayList.add(training);
                }
                // move the cursor's pointer up one position.
                while (cursor.moveToNext());
            }

Answer 3

<强>问题：

您要将数据分配到Training课程中Portfolio的同一个实例。

Training training = Training.getInstance();

以上行将为您提供相同的实例，并且每次都将此相同的引用添加到ArrayList。由于对象是静态的，这就是为什么最后一次迭代的数据将在Training类变量中更新，因此你得到google和google，因为google是你最后一次迭代的数据。

<强>解决方案：

在每次迭代中创建新的Training对象，如下所示：

Training training = new Training();

Answer 4

您只是创建了Training对象的一个实例。实际上，您已经实现了单例模式。每次将光标前进到下一条记录时都要创建一个新的Training对象 -

if (cursor.moveToFirst()) {

    while (cursor.isAfterLast() == false) {


        Training training = new Training(cursor.getInt(cursor
                .getColumnIndex(DatabaseHelper.TRAINING_ID)),
                cursor.getString(cursor
                .getColumnIndex(DatabaseHelper.TRAINING_TITLE))
                cursor.getString(cursor
                .getColumnIndex(DatabaseHelper.TRAINING_DESCRIPTION))
                cursor.getString(cursor
                .getColumnIndex(DatabaseHelper.TRAINING_DATE))
                cursor.getString(cursor
                .getColumnIndex(DatabaseHelper.TRAINING_LOCATION))
            );
        this.trainingArrayList.add(training);
        cursor.moveToNext();
    }


public class Training {

private static Training instance = null;

// global variables
public int id;
public String title;
public String description;
public String date;
public String location;
private Trainer trainer;

private ArrayList<Trainee> traineeArrayList;

public Training(int id, String title, String description, String date, String location) {
  this.id = id;
  this.title = title;
  this.description = description;
  this.date = date; 
  this.location = location;
}

只在arraylist中获得最后一行

4 个答案: