Question

我不明白为什么我的笔记应用程序不断崩溃。我单击一个按钮以插入一个注释，该注释使用SQLite数据库显示在listView中。

给出的错误是：

(1) no such column: TITLE
 FATAL EXCEPTION: main
Unable to resume activity: android.database.sqlite.SQLiteException: no such column: TITLE (code 1 SQLITE_ERROR): , while compiling: SELECT ID, TITLE FROM note_table

位于mainactivity.java中的此处：

cursor = database.query(table_name, columns, where, where_args, group_by, having, order_by);

数据库：

public class DBOpenHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "notes.db";
public static final String TABLE_NAME = "note_table";
public static final String ID_COLUMN = "ID";
public static final String TITLE_COLUMN = "TITLE";
public static final String TEXT_COLUMN = "ITEM2";
public static final String DATE_COLUMN = "DATE";

SQLiteDatabase db = this.getWritableDatabase();



public DBOpenHelper(Context context) {
    super(context, DATABASE_NAME, null, 1);
}

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

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("drop table notes_table");
    onCreate(db);
}

Mainactivity.java：

public class MainActivity extends AppCompatActivity {
private ListView listView;
private ArrayList<String> notes_list;
private ArrayAdapter adapter;
private DBOpenHelper helper;
private SQLiteDatabase database;
private TextView noNotesView;
private Cursor cursor;

@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(MainActivity.this, Edit_notes.class);
            startActivity(intent);
        }
    });
    noNotesView = findViewById(R.id.empty_notes);

    listView = (ListView) findViewById(R.id.listView);
    notes_list = new ArrayList<>();
    helper = new DBOpenHelper(this);
    database = helper.getWritableDatabase();
}

private void ViewData(){

    String table_name = "note_table";
    String[] columns = {"ID", "TITLE"};
    String where = null;
    String where_args[] = null;
    String group_by = null;
    String having = null;
    String order_by = null;
    cursor = database.query(table_name, columns, where, where_args, group_by, having, order_by); // the error is here

    String total_text = "total number of rows: " + cursor.getCount() + "\n";
    cursor.moveToLast();

    notes_list = new ArrayList<>();
    adapter = new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,notes_list);

    for(int i = 0; i < cursor.getCount(); i++) {
     //   total_text += c.getInt(0) + " " + c.getString(1) + "\n";
        notes_list.add(cursor.getString(1));
        listView.setAdapter(adapter);
        cursor.moveToPrevious();
    }
//    noNotesView.setText(total_text);
}

private void hide_or_show() {
    if (cursor.getCount() == 0) {
        noNotesView.setVisibility(View.VISIBLE);
    } else {
        noNotesView.setVisibility(View.GONE);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.delete_all) {
        Delete_all();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onResume()
{
    super.onResume();
    ViewData();
    hide_or_show();
}

public void Delete_all() {
    database.execSQL("delete from " + "note_table");
    adapter.clear();
}

由于列名正确，我不明白为什么收到此错误消息。我尝试删除并重新编译我的应用程序，但没有成功。

Answer 1

您的问题出在数据库类的构造函数上：

public DBOpenHelper(Context context) {
    super(context, DATABASE_NAME, null, 1);
}

特别是1的最后一个参数中的super()。那是您的数据库版本，是对数据库结构进行更改的关键。您在评论中提到TITLE以前称为ITEM1，但在您的设备上它仍称为ITEM1，因为您的应用程序不知道数据库结构已更改。

您可以通过在类中引入版本常量来解决此问题，如下所示：

private static final int DB_VERSION = 2;

并在构造函数中使用此变量：

public DBOpenHelper(Context context) {
    super(context, DATABASE_NAME, null, DB_VERSION);
}

无论何时对数据库进行任何结构更改，都应递增DB_VERSION，这将导致SQLiteOpenHelper调用其onUpgrade()方法。

Android Studio没有这样的列SQL数据库

1 个答案: