Error - Use the "New" keword to create the object, Object Reference not set to an instance

Question

4.00/5 (2 votes)

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Errors are - 1 ) Use the "New" keword to create the object
2) Object Reference not set to an instance

Error is giving in this line -

C#

rs = ds.Tables["registration"].Select("email='" + sa + "'");

My code in cs is

protected void Button1_Click(object sender, EventArgs e)
    {
        SqlConnection CON = new SqlConnection(System.Web.Configuration.WebConfigurationManager.ConnectionStrings["tuitionConnectionString"].ConnectionString);
        CON.Open();
        ds = new DataSet();
        string sql = "select *  from registration";
        da = new SqlDataAdapter(sql, CON);
        da1 = new SqlDataAdapter(sql, CON);
        string sa = txtEmail.Text;
        string pw = txtPass.Text;
        int r = 0, r1 = 0;
        DataRow[] rs;
        DataRow[] rs1;
        rs = ds.Tables["registration"].Select("email='" + sa + "'");
        r = rs.Length;
        
        rs1 = ds.Tables["registration"].Select("pass='" + pw + "'");
        r1 = rs1.Length;
        
        if (r!=0 && r1!=0)
        {
            txtEmail.Text = r.ToString();
            txtPass.Text = r1.ToString();
          
        }
        else
        {
            System.Web.UI.WebControls.Label lbl1 = new System.Web.UI.WebControls.Label();
            lbl1.ForeColor = System.Drawing.Color.Yellow;
            lbl1.BackColor = System.Drawing.Color.Blue;
            lbl1.Text = "Please Enter a Valid User ID and Password";
            ph1.Controls.Add(lbl1);
        }
        CON.Close();
    }

[edit]Code block added, "Treat my content as plain text..." option disabled - OriginalGriff[/edit]

Posted 18-Dec-11 21:12pm

Janardan Pandey

Updated 18-Dec-11 21:14pm

OriginalGriff

v2

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4 solutions

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Amir Mahfoozi · Answer 1 · 2011-12-18T21:24:00

Solution 4

Put a break point at that line and when program execution reached to that point check whether ds.Tables["registration"] or sa not to be null.
If one of them where null do proper actions .

Hope it helps.

Posted 18-Dec-11 21:24pm

Amir Mahfoozi

Abhinav S · Answer 2 · 2011-12-18T21:24:00

Solution 3

You need to look at how to populate a Dataset[^].

Use the fill method of the Data Adapter on the Dataset.
Something like

da.fill(ds,"registration");

Posted 18-Dec-11 21:24pm

Abhinav S

OriginalGriff · Answer 3 · 2011-12-18T21:20:00

Look at your code:

C#

ds = new DataSet();
string sql = "select *  from registration";
da = new SqlDataAdapter(sql, CON);
da1 = new SqlDataAdapter(sql, CON);
string sa = txtEmail.Text;
string pw = txtPass.Text;
int r = 0, r1 = 0;
DataRow[] rs;
DataRow[] rs1;
rs = ds.Tables["registration"].Select("email='" + sa + "'");

Taking out all the lines which do not refer to (and thus affect) ds in any way:

ds = new DataSet();
rs = ds.Tables["registration"].Select("email='" + sa + "'");

Which means that you are ctreateing a new, empty DataSet, and then trying to use a table from it. It is empty, so no tables, so you get the "object Reference..." error.
I suspect that you need an SqlDataAdapter.Fill(ds) from either da or da1 before you try to use the DataSet.
I don't know why you have two identical SqlDataAdapters, though...

Sergey Alexandrovich Kryukov · Answer 4 · 2011-12-18T21:19:00

Solution 1

It looks like ds.Tables["registration"] returns null. You could have misspelled this hard-coded string index or something like that. Not a big deal. Always use the Debugger to avoid such problems. And such questions, by the way.

"Use 'new'…" is a bogus suggestion. Sometime you need to use "new", sometimes not.

—SA

Posted 18-Dec-11 21:19pm

Sergey Alexandrovich Kryukov

Updated 18-Dec-11 21:21pm

v3

Comments

Amir Mahfoozi 19-Dec-11 3:26am

+5

Sergey Alexandrovich Kryukov 19-Dec-11 4:08am

Thank you, Amir.
--SA

koolprasad2003 19-Dec-11 3:35am

Yes, simple ds.Tables["registration"] is NULL. 5.