System.NullReferenceException: Object reference not set to an instance of an object.

this is same as your previous question...

apply the same thing here...

https://www.experts-exchange.com/questions/29049777/System-NullReferenceException-Object-reference-not-set-to-an-instance-of-an-object.html?notificationFollowed=195837547&anchorAnswerId=42250239#a42250239

but it is a searching from database how i do it?

which line is giving that error?
put a breakpoint and see all the variables and expressions on that line to see what is wrong

from your codes posted, without the actual logic, few variables to check and make sure they are not null.

• Session["JOBCATE"]
• Session["QUALI"]
• Session["skill"]
• CDT.Rows[0]["CID"]

As mentioned by HainKurt, place the break points so that you know which line hits the error

Your first line makes a lot of assumptions without checking the nullability of many object/property references:

CDT = Cadapter.SELECT_SEARCH_COMPANY(Session["JOBCATE"].ToString(), Session["QUALI"].ToString(), Session["skill"].ToString());

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As others have stated, you need to check your many references, namely:

• Cadapter
• Session["JOBCATE"]
• Session["QUALI"]
• Session["skill"]

This would essentially look like:

protected void Page_Load(object sender, EventArgs e)
{
    var jobcate = Session["JOBCATE"];
    var quali = Session["QUALI"];
    var skill = Session["skill"];

    if (Cadapter != null && jobcate != null && quali != null && skill != null)
    {
        CDT = Cadapter.SELECT_SEARCH_COMPANY(jobcate.ToString(), quali.ToString(), skill.ToString());
        if (CDT != null)
        {
            if (CDT.Rows.Count > 0)
            {
                Session["CID"] = CDT.Rows[0]["CID"].ToString();
            }
            else
            {
                DataList3.DataSource = CDT;
                DataList3.DataBind();
            }
        }
    }
}

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-saige-