未将对象引用设置到对象的实例。 
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异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。

源错误: 


行 864:              #endregion
行 865:               // DataSet ds = FileManager_B.GetAllFileByFolderID(int.Parse(InfoUser_FolderList.Items[i].Value));
行 866:                for (int j = 0; j < ds_FileList.Tables[0].Rows.Count; j++)
行 867:                {
行 868:                    for (int k = 0; k < InfoUser_FileList.Items.Count; k++)
 

 protected void InfoUser_FolderList_SelectedIndexChanged(object sender, EventArgs e)
    {
        for (int i = 0; i < InfoUser_FolderList.Items.Count; i++)
        {         
            DataSet ds_FileList = FileManager_B.GetAllFileByFolderID(int.Parse(InfoUser_FolderList.Items[i].Value));

            if (InfoUser_FolderList.Items[i].Selected)
            {
                for (int j = 0; j < ds_FileList.Tables[0].Rows.Count; j++)
                {
                    for (int k = 0; k < InfoUser_FileList.Items.Count; k++)
                    {
                        if (InfoUser_FileList.Items[k].Value == ds_FileList.Tables[0].Rows[j]["ID"].ToString())
                        {
                            InfoUser_FileList.Items[k].Selected = true;
                        }
                    }
                }
            }
            else
            {
                for (int j = 0; j < ds_FileList.Tables[0].Rows.Count; j++)
                {
                    for (int k = 0; k < InfoUser_FileList.Items.Count; k++)
                    {
                        if (InfoUser_FileList.Items[k].Value == ds_FileList.Tables[0].Rows[j]["ID"].ToString())
                        {
                            InfoUser_FileList.Items[k].Selected = false;
                        }
                    }
                }
            }
        }
    }