Question

我是android开发的新手。我想要的是从存储在数据库中的值填充我的列表。为此我创建了一个带有insert和select语句的数据库。同时我创建了一个模型来保存data。从列表适配器我已经将数据插入到数据库中，但是当我尝试检索该数据时，我得到了空。

DataBase Class

public class DbHandler extends SQLiteOpenHelper {

    private static final int dbVersion = 1;
    private static final String dbName = "HSsuraksha";
    private static final String tableName = "pocketDocs";
    private static final String userId = "userId";
    private static final String docId = "docId";
    private static final String fileName = "fileName";
    private static final String fileExt = "fileExt";
    private static final String title = "title";

    private static final String createTable = "CREATE TABLE " + tableName + "(" + userId + " Integer Primary Key," + docId + " Integer," + fileName + " Text," + fileExt + " Text," + title + " Text" + ")";

    public DbHandler(Context context) {
        super(context, dbName, null, dbVersion);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i2) {

    }

    public void insertData(DbModel dbModel) {
        SQLiteDatabase database = getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        database.beginTransaction();
        contentValues.put(userId, dbModel.userId);
        contentValues.put(docId, dbModel.docId);
        contentValues.put(fileName, dbModel.fileName);
        contentValues.put(fileExt, dbModel.fileExtension);
        contentValues.put(title, dbModel.title);
        if (contentValues != null) {
            Long id = database.insert(tableName, null, contentValues);
            Log.e("insert values", "" + id);
        }

        database.endTransaction();
        database.close();

    }

    public DbModel selectDocs(String id) {
        SQLiteDatabase db = this.getReadableDatabase();
        DbModel model = new DbModel();
        Cursor cursor = db.query(tableName, new String[]{fileName, fileExt, title}, docId + "=?", new String[]{id}, null, null, null, null);
        if (cursor.moveToFirst()) {
            model.fileName = cursor.getString(2);
            model.fileExtension = cursor.getString(3);
            model.title = cursor.getString(4);
        }
        db.close();
        return model;
    }
}

数据库模型

public class DbModel implements Serializable {
    public String userId, docId, fileName, fileExtension, title;

    public DbModel() {
    }

    public DbModel(String userId, String docId, String fileName, String fileExtension, String title) {
        this.userId = userId;
        this.docId = docId;
        this.fileName = fileName;
        this.fileExtension = fileExtension;
        this.title = title;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getDocId() {
        return docId;
    }

    public void setDocId(String docId) {
        this.docId = docId;
    }

    public String getFileName() {
        return fileName;
    }

    public void setFileName(String fileName) {
        this.fileName = fileName;
    }

    public String getFileExtension() {
        return fileExtension;
    }

    public void setFileExtension(String fileExtension) {
        this.fileExtension = fileExtension;
    }

    public String getTitle() {
        return title;
    }

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

ListAdapter

public View getView(int i, View view, ViewGroup viewGroup) {
        final ViewHolder holder;
        dbHandler = new DbHandler(context);
        dbModel = new DbModel("1", "1", "GoogleDocs", ".pdf", "Test");

        dbHandler.insertData(dbModel);
        if (view == null) {
            holder = new ViewHolder();
            view = LayoutInflater.from(context).inflate(R.layout.view_docs_custom_list, viewGroup, false);
            holder.docsImage = (ImageView) view.findViewById(R.id.iv_docs_image);
            holder.tvTitle = (TextView) view.findViewById(R.id.tv_file_name);
            holder.tvPostedOn = (TextView) view.findViewById(R.id.tv_posted_on);
            holder.btShare = (Button) view.findViewById(R.id.bt_share);
            view.setTag(holder);
        } else {
            holder = (ViewHolder) view.getTag();
        }


        dbHandler.selectDocs(dbModel.getDocId());    // here i am getting the values from db and displaying it in the list

        holder.tvTitle.setText(dbModel.title);

Answer 1

更改

 model.fileName = cursor.getString(2);
 model.fileExtension = cursor.getString(3);
 model.title = cursor.getString(4);

到

 model.fileName = cursor.getString(cursor.getColumnIndexOrThrow(fileName));
 model.fileExtension = cursor.getString(cursor.getColumnIndexOrThrow(fileExt));
 model.title = cursor.getString(cursor.getColumnIndexOrThrow(title));

getString基于零索引。它取决于您在query中提到的列数，而不是您在CREATE声明中使用它们的顺序

如果您尝试

cursor.getString(3);

你应该得到IllegalStateException陈述

java.lang.IllegalStateException: Couldn't read row 0, col 3 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.

因为您尝试访问cursor中的第4列，而它只有3列

选择语句不工作sqlite android

1 个答案: