android - 应用程序因 java.lang.IllegalArgumentException : column '_id' does not exist 而崩溃

Question

我正在制作一个从数据库中填充 ListView 的应用程序。但是每当我运行它时，应用程序都会因 java.lang.IllegalArgumentException: column '_id' does not exist 而崩溃。首先，我没有字段 ID。然后我做了一些谷歌搜索，发现我必须在使用 SimpleCursorAdapter 时添加 _id 。但问题仍然存在..

 private static final String TABLE_CLASS_LIST = "classlist";

 //class list column names
    private static final String KEY_LIST_ID = "_id";
    private static final String KEY_SUBJECT_NAME_LIST = "subjectname";
    private static final String KEY_CLASS_DIV_LIST = "classdivision";


private static final String CREATE_CLASS_LIST = "CREATE TABLE "
            + TABLE_CLASS_LIST + "(" + KEY_LIST_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_SUBJECT_NAME_LIST
            + " TEXT," + KEY_CLASS_DIV_LIST + " TEXT)";



public void addClassList(ClassList classList) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(KEY_SUBJECT_NAME_LIST, classList.getSubject());
    values.put(KEY_CLASS_DIV_LIST, classList.getClassd());
    //  values.put(KEY_CREATED_AT, user.getCreated_at());

    // insert row
    long user_id = db.insert(TABLE_CLASS_LIST, null, values);


}


public Cursor fetchTableList() {
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor mCursor = db.query(TABLE_CLASS_LIST, new String[]{KEY_SUBJECT_NAME_LIST,
                    KEY_CLASS_DIV_LIST},
            null, null, null, null, null);

    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;
}

以上是我的 dbhelper 类(不是全部)。

还有我的 Activity

public class ClassActivity extends ActionBarActivity {
    ListView classlist;

    String value;
    private SimpleCursorAdapter dataAdapter;
    DatabaseHelper databaseHelper;
    Cursor cursor;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_class); 
    classlist = (ListView) findViewById(R.id.listClass);
    databaseHelper = new DatabaseHelper(this);
    String[] arrayColumns = new String[]{"classdivision", "subjectname"};
    int[] arrayViewIDs = new int[]{R.id.classid, R.id.subject};

    cursor = databaseHelper.fetchTableList();
    dataAdapter = new SimpleCursorAdapter(
            this, R.layout.classlist_single_item,
            cursor,
            arrayColumns,
            arrayViewIDs,
            0);


    classlist.setAdapter(dataAdapter);
    value = getIntent().getExtras().getString("add");

Answer 1

您的查询投影缺少 _id 字段，

改变

 Cursor mCursor = db.query(TABLE_CLASS_LIST, new String[] { KEY_SUBJECT_NAME_LIST, KEY_CLASS_DIV_LIST},
        null, null, null, null, null);

到

 Cursor mCursor = db.query(TABLE_CLASS_LIST, new String[] { KEY_LIST_ID, KEY_SUBJECT_NAME_LIST, KEY_CLASS_DIV_LIST},
        null, null, null, null, null);