从数据库列中获取值

Question

我正在尝试获取列 threadid 的值，其中 id（它是唯一的）等于我发送到 getthreadid 函数的 id。threadid 包含 long 数据类型的值，但我不知道为什么我的应用程序在执行此操作时崩溃，请帮助，提前致谢。

long id;
long threadid = datasource.getthreadid(id);
Toast.makeText(getActivity(), String.valueOf(threadid), Toast.LENGTH_SHORT).show();

public long getthreadid(long id)
{
    String ide = String.valueOf(id);
    String queryz = "SELECT " + "," + MySQLiteHelper.COLUMN_THREADID 
        + " FROM " + MySQLiteHelper.TABLE_NAME 
        + " WHERE " + MySQLiteHelper.COLUMN_ID + "=" + ide;
    Cursor cursor = database.rawQuery(queryz, null);
    long threadid = cursor.getLong(cursor.getColumnIndex("threadid"));
    return threadid;
}

我的数据库创建查询是：

static final String DATABASE_CREATE = "create table "+"message"+
            "( " +"id"+" integer primary key autoincrement,"+ "threadid long,parentid integer,message  text not null,messagestatus text); ";

Answer 1

我认为您的查询错误

 String queryz = "SELECT " + "," + MySQLiteHelper.COLUMN_THREADID 
        + " FROM " + MySQLiteHelper.TABLE_NAME 
        + " WHERE " + MySQLiteHelper.COLUMN_ID + "=" + ide;

预期输出“SELECT , COLUMN FROM TABLE WHERE COLUMNID = VALUE” 查询错误

应该是这个

  String queryz = "SELECT " + MySQLiteHelper.COLUMN_THREADID 
            + " FROM " + MySQLiteHelper.TABLE_NAME 
            + " WHERE " + MySQLiteHelper.COLUMN_ID + "=" + ide;

预期输出“SELECT COLUMN FROM TABLE WHERE COLUMNID = VALUE”

检查您的 database!=null，然后检查 database.isOpen()，如果执行

检查您的 cursor!= null，然后检查 cursor.getCount() > 0