从 Android Studio 中的 SQLite 数据库中以字符串形式检索数据

Question

我想将名称保存在 SQLite 数据库中，稍后在另一个活动中我想将该名称作为字符串值检索。但我无法从数据库中获取数据。请帮帮我。我的代码如下，

数据库助手：

    private static final String TAG = "DatabaseHelper";
    private static final String TABLE_NAME = "user";
    private static final String COL1 = "ID";
    private static final String COL2 = "name";

    public void onCreate(SQLiteDatabase db) {String createTable = 
    "CREATE TABLE " + TABLE_NAME + " (ID INTEGER PRIMARY KEY 
    AUTOINCREMENT, " + COL2 +" TEXT)"; 
    db.execSQL(createTable);}

    public boolean addData(String item) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues = new ContentValues();
    contentValues.put(COL2, item);

            Log.d(TAG, "addData: Adding " + item + " to " + TABLE_NAME);

            long result = db.insert(TABLE_NAME, null, contentValues);

            if (result == -1) {
                return false;
            } else {
                return true;
            }
        }

主活动：

    mDatabaseHelper=new DatabaseHelper(this);
    Username=(EditText)findViewById(R.id.user);
    saveBtn=(Button)findViewById(R.id.button);

    saveBtn.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
    String newEntry = Username.getText().toString();
                            AddData(newEntry);
                            Username.setText("");

    Intent intent = new Intent(MainActivity.this, HomeActivity.class);
                        startActivity(intent);
                    }
                });

            }
            public void AddData(String newEntry) {
                boolean insertData = mDatabaseHelper.addData(newEntry);
        }
        }

家庭活动：

public class HomeActivity extends AppCompatActivity {

    DatabaseHelper mDatabaseHelper;
    String Username;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);

        mDatabaseHelper = new DatabaseHelper(this);

    }

}

在这里，在这个家庭活动中，我想将用户名作为字符串获取，但我不知道该怎么做。请帮帮我...

Answer 1

要检索数据，请运行将数据提取到光标中的查询。游标将由 0-n 行组成，并且将具有查询中定义的尽可能多的列。然后您移动行并使用适当的光标get?????方法获取实际数据。

例如，您可以将以下方法添加到 DatabaseHelper 中：-

public String getName(long id) {

    String rv = "not found";
    SqliteDatabase db = this.getWritableDatabase();
    String whereclause = "ID=?";
    String[] whereargs = new String[]{String.valueOf(id)};
    Cursor csr = db.query(TABLE_NAME,null,whereclause,whereargs,null,null,null);
    if (csr.moveToFirst()) {
        rv = csr.getString(csr.getColumnIndex(COL2));
    }
    return rv;
}

String name = mDatabaseHelper.getName(1); 可以使用上述内容。

• 请注意，这假定存在 ID 为 1 的行。

Answer 2

您的数据库助手：

    private static final String TAG = "DatabaseHelper";
    private static final String TABLE_NAME = "user";
    private static final String COL1 = "ID";
    private static final String COL2 = "name";



private static final String createTable = "CREATE TABLE " + TABLE_NAME + " (" + COL1 +" INTEGER PRIMARY KEY AUTOINCREMENT, " + COL2 +" TEXT)"; // You have written ID inplace of COL1






 public  DatabaseHelper(Context context)
    {

        super(context,DB_NAME,null,1);
    }

 public void onCreate(SQLiteDatabase db)
    {
        db.execSQL(createTable);

    }

public boolean insertData(String name) {

    SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
    ContentValues contentValues1 =  new ContentValues();
    contentValues1.put(COL2,name);


    long result1 = sqLiteDatabase.insert(TABLE_NAME,null,contentValues1);
    return result1 != -1;
}
public Cursor viewData()
{
    SQLiteDatabase sqLiteDatabase = this.getReadableDatabase();
    Cursor cursor ;

    String query = "Select * from " +TABLE_NAME;
    cursor= sqLiteDatabase.rawQuery(query, null);


    return cursor;
}

您的主要活动：

 mDatabaseHelper=new DatabaseHelper(this);
    Username=(EditText)findViewById(R.id.user);
    saveBtn=(Button)findViewById(R.id.button);

    saveBtn.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
    String newEntry = Username.getText().toString();
                            mDatabaseHelper.insertData(newEntry);
                            Username.setText("");

    Intent intent = new Intent(MainActivity.this, HomeActivity.class);
                        startActivity(intent);
                    }
                });

            }

        }

您的家庭活动：

public class HomeActivity extends AppCompatActivity {

    DatabaseHelper mDatabaseHelper;
    String Username;


ArrayList<String> listItem;
    ArrayAdapter adapter;
    ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);

        mDatabaseHelper = new DatabaseHelper(this);
listView = (ListView) findViewById(R.id.listView);
        listItem = new ArrayList<>();
viewData1();

    }

private void viewData1() {

        Cursor cursor = mDatabaseHelper.viewData();

        if (cursor.getCount() == 0) {

            Toast.makeText(this, "No data to show", Toast.LENGTH_SHORT).show();
        } else {
            while (cursor.moveToNext()) {
                Log.i("message","Data got");

                listItem.add(cursor.getString(1)); // Adding data received to a Listview
            }
            adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listItem);
            listView.setAdapter(adapter);

        }
    }

    }

Answer 3

看看这个库

很容易实现

https://github.com/wisdomrider/SqliteClosedHelper