待办APP中搜索框清空后RecyclerView列表项消失的问题咨询

你的问题核心出在SQLiteDataBaseClass的getTask()方法中：遍历Cursor创建TaskModel对象后，没有将创建好的任务对象添加到返回的列表里，导致搜索框清空时，适配器拿到的是空列表，RecyclerView自然没有数据可显示。

修复后的getTask()方法 #

// SQLite类中返回任务列表的方法
public List<TaskModel> getTask() {
    List<TaskModel> taskModel = new ArrayList<>();
    SQLiteDatabase sqLiteDatabase = getReadableDatabase();
    Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM " + TABLE_TASK, null);
    if (cursor.moveToFirst()) {
        do {
            TaskModel task = new TaskModel();
            task.setId(cursor.getLong(0));
            task.setTitle(cursor.getString(1));
            task.setCompleted(cursor.getInt(2) == 1);
            // 新增这行：把创建好的任务对象添加到列表中
            taskModel.add(task);
        } while (cursor.moveToNext());
    }
    // 关闭Cursor避免资源泄漏
    cursor.close();
    sqLiteDatabase.close();
    return taskModel;
}

额外优化建议 #

1. 规避SQL注入风险：当前searchBox()方法用字符串拼接SQL语句，存在注入漏洞，建议改用参数绑定的写法：

public List<TaskModel> searchBox(String query) {
    List<TaskModel> taskModel = new ArrayList<>();
    SQLiteDatabase sqLiteDatabase = getReadableDatabase();
    // 使用?作为占位符，避免SQL注入
    Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM " + TABLE_TASK + " WHERE title LIKE ?", 
            new String[]{"%" + query + "%"});
    if (cursor.moveToFirst()) {
        do {
            TaskModel task = new TaskModel();
            task.setId(cursor.getLong(0));
            task.setTitle(cursor.getString(1));
            task.setCompleted(cursor.getInt(2) == 1);
            taskModel.add(task);
        } while (cursor.moveToNext());
    }
    cursor.close();
    sqLiteDatabase.close();
    return taskModel;
}

2. 安全管理IO资源：Cursor和SQLiteDatabase属于IO资源，推荐用try-with-resources语法自动关闭，降低资源泄漏概率：

public List<TaskModel> getTask() {
    List<TaskModel> taskModel = new ArrayList<>();
    try(SQLiteDatabase sqLiteDatabase = getReadableDatabase();
        Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM " + TABLE_TASK, null)) {
        if (cursor.moveToFirst()) {
            do {
                TaskModel task = new TaskModel();
                task.setId(cursor.getLong(0));
                task.setTitle(cursor.getString(1));
                task.setCompleted(cursor.getInt(2) == 1);
                taskModel.add(task);
            } while (cursor.moveToNext());
        }
    }
    return taskModel;
}

内容的提问来源于stack exchange，提问作者Ehsan Taghizadeh