从数据库中查看 ListView 中的项目

Posted 2023-04-19

【中文标题】从数据库中查看 ListView 中的项目

【英文标题】：Viewing Items in a ListView from Database

【发布时间】：2015-12-28 15:37:35

【问题描述】：

我正在 android Studio 中开发一个 android 应用程序。在这个函数中，我想将 ListView 中的项目保存到数据库中，并在另一个 java 页面上的 listView 中查看它。现在可以将arraylist中的元素添加到数据库部分，因为logcat正在工作。现在我想在另一个页面上查看它。我已经为此实现了一个代码。但是当我单击查看按钮时，它没有给出任何响应。下面我发布了 DBAdapter 类和 java 类的代码。谢谢:)

viewHistory.java

public class viewHistoryScr extends Activity implements View.OnClickListener
private Button viewHist;
private Button back;
private ListView historyView;
DBUserAdapter dbUserAdapter = new DBUserAdapter(viewHistoryScr.this);
String username = DBUserAdapter.KEY_USERNAME;

@Override
protected void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.historyitmscr);
    viewHist = (Button) findViewById(R.id.viewHistory);
    back = (Button) findViewById(R.id.goBack);
    historyView = (ListView) findViewById(R.id.historyList);
    viewHist.setOnClickListener(this);
    back.setOnClickListener(this);


private void viewHistoryItm()
    Cursor cursor = dbUserAdapter.viewItm(username);
    List<String> values = new ArrayList<String>();
    if (cursor != null && cursor.moveToFirst())
        do 
            String itmName = cursor.getString(Integer.parseInt(DBUserAdapter.KEY_ITMNAME));

            //String[]values = new String[]itmName;
            values.add(itmName);
            ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.historyitmscr, R.id.historyList, values);
            historyView.setAdapter(adapter);
            cursor.close();
        
        while (cursor.moveToNext());
    


@Override
public void onClick(View view) 
    if (view.getId() == R.id.addItems) 
        try 
            dbUserAdapter.open();
            viewHistoryItm();
            dbUserAdapter.close();
         catch (SQLException e) 
            e.printStackTrace();
        
    
    else if (view.getId() == R.id.goBack)
        Intent i = new Intent(viewHistoryScr.this, MainActivity.class);
        startActivity(i);
    

---

DBUserAdapter.java

---

public class DBUserAdapter
public static final String KEY_ROWID = "_id";
public static final String KEY_USERNAME = "username";
public static final String KEY_PASSWORD = "password";
public static final String KEY_PASSHINT = "passHint";
public static final String KEY_ITMNAME = "itmName";
//public static final String KEY_ITMNAME = ""
public static final String TAG = "DBAdapter";

String userN = KEY_USERNAME;

String manualUser = KEY_USERNAME;

public static final String DATABASE_NAME = "usersdb";
public static final String DATABASE_TABLE = "userInfo";
public static final String ITM_DATABASE_NAME = "manualItm";
public static final int DATABASE_VERSION = 320;

public static final String DATABASE_CREATE = "CREATE TABLE "+DATABASE_TABLE+"(username TEXT NOT NULL, password TEXT NOT NULL, passHint TEXT NOT NULL);";
public static final String ITM_DATABASE_CREATE = "CREATE TABLE "+ITM_DATABASE_NAME+"(username TEXT NOT NULL, itmName TEXT NOT NULL)";

private Context context = null;
private DatabaseHelper dbHelper;
public SQLiteDatabase db;

public DBUserAdapter(Context context)
    this.context = context;
    dbHelper = new DatabaseHelper(context);


private static class DatabaseHelper extends SQLiteOpenHelper
    DatabaseHelper(Context context)
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    

    @Override
    public void onCreate(SQLiteDatabase db) 
        db.execSQL(DATABASE_CREATE);
        db.execSQL(ITM_DATABASE_CREATE);
    

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
        Log.w(TAG, "Upgrading Database from Version "+oldVersion+" to "+newVersion+", Which will Destroy all old Data");
        db.execSQL("DROP TABLE IF EXISTS userInfo");
        db.execSQL("DROP TABLE IF EXISTS manualItm");
        onCreate(db);
    


public void open() throws SQLException
    db = dbHelper.getWritableDatabase();


public void close()
    db.close();


public SQLiteDatabase getDatabaseInstance()
    return db;


public boolean AddUser(String username, String password, String passHint)
    try 
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_USERNAME, username);
        initialValues.put(KEY_PASSWORD, password);
        initialValues.put(KEY_PASSHINT, passHint);
        db.insert(DATABASE_TABLE, null, initialValues);
        db.close();
        return true;
    
    catch (Exception e)
        e.printStackTrace();
    
    return false;


public boolean Login(String username, String password) throws SQLException
    Cursor cursor = db.rawQuery("SELECT * FROM " + DATABASE_TABLE + " WHERE username=? AND password=?", new String[]username, password);
        if(cursor != null)
        if (cursor.getCount() > 0)
            return true;
        
    
    return false;


public boolean register(String username, String password, String passHint)throws SQLException
    Cursor cursor = db.rawQuery("INSERT INTO " + DATABASE_TABLE + " VALUES('?', '?', '?', '?');", new String[]username, password, passHint);
    if(cursor != null)
        if(cursor.getCount() > 0)
            return true;
        
    
    return false;



public void insertItm(ArrayList<String>itemsList)
    try
        db = dbHelper.getWritableDatabase();
        for (int a = 0; a < itemsList.size(); a++)
            ContentValues contentValues = new ContentValues();
            contentValues.put(KEY_ITMNAME, itemsList.get(a));
            contentValues.put(KEY_USERNAME, manualUser);
            db.insert(ITM_DATABASE_NAME, null, contentValues);
        
        db.close();
    
    catch (Exception ex)
        Log.e("Error in Adding Items", ex.toString());
    


//public boolean viewItm(String userN)
    //String WHERE = KEY_USERNAME + "=" + username;
 //   Cursor cursor = db.rawQuery("SELECT * FROM " + ITM_DATABASE_NAME + " WHERE username=?", new String[]userN);
//    if(cursor != null)
 //       cursor.moveToFirst();
 //       return true;
//    
//    return false;
//

public Cursor viewItm(String userN)
    Cursor cursor = db.rawQuery("SELECT * FROM " + ITM_DATABASE_NAME + " WHERE username=?", new String[]userN);
    if (cursor != null)
        cursor.moveToFirst();
    
    return cursor;

【参考方案1】：

设置Adpater Outside 和Cursor.close() while 循环，或者每次它都会创建新的适配器并关闭光标，这样下次它就会返回null，就像

 private void viewHistoryItm()
        Cursor cursor = dbUserAdapter.viewItm(username);
        List<String> values = new ArrayList<String>();
        if (cursor != null && cursor.moveToFirst())
            do 
                String itmName = cursor.getString(Integer.parseInt(DBUserAdapter.KEY_ITMNAME));

                //String[]values = new String[]itmName;
                values.add(itmName);

            
            while (cursor.moveToNext());
          ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.historyitmscr, R.id.historyList, values);
                historyView.setAdapter(adapter);
                cursor.close();