can't see next previous or last and first records

Question

1.00/5 (1 vote)

See more:

I am trying this tutorial from online to add delete search and navigate a database. I have successfully made the connection. I could call the NavitegateRecords from Form_load But btnNext or btnLast such is not happening. Im getting a NullReferenceException bcoz the dRow has null value. Also just to check if correct value is passed I used a messageBox to check the content of objConnect.Sql...But this is giving an error saying "property cannot be used in this context because it lacks the get accessor"(So I not understanding how to solve it commented it out for the time being). My code is as follows:

C#

    DatabaseConnection objConnect;
    string conString;

    DataSet ds;
    DataRow dRow;
        
    int MaxRows;
    int inc = 0;
    SqlConnection cnn = new SqlConnection();
    SqlDataAdapter daAdapter = new SqlDataAdapter();
        
    private void Form1_Load(object sender, EventArgs e)
    {
        DataSet ds=new DataSet();
        String SQ;
            
        objConnect = new DatabaseConnection();
        conString = Properties.Settings.Default.EmployeesConnectionString;
        //MessageBox.Show(conString);
        objConnect.connection_string = conString;
        SQ=Properties.Settings.Default.SQL;
        objConnect.Sql = SQ;
        MessageBox.Show(objConnect.Sql);
        ds = objConnect.GetConnection;
                
        MaxRows = ds.Tables[0].Rows.Count;
        MessageBox.Show(MaxRows.ToString());
        try
        {
            NavigateRecords(ds);
        }
        catch (Exception err)
        {
            MessageBox.Show(err.Message);
        }
    }
    private void NavigateRecords(DataSet ds)
    {
        dRow = ds.Tables[0].Rows[inc];
                       
        txtFirstName.Text = dRow.ItemArray.GetValue(1).ToString();
        txtSurname.Text = dRow.ItemArray.GetValue(2).ToString();
        txtJobTitle.Text = dRow.ItemArray.GetValue(3).ToString();
        txtDepartment.Text = dRow.ItemArray.GetValue(4).ToString();
    }

private void btnNext_Click(object sender, EventArgs e)
    {
        if (inc != (MaxRows-1))
        {
           inc= inc+1;
            NavigateRecords(ds);
        }
        else
        {
            if (inc != (MaxRows - 1))
            {
                inc = (MaxRows-1);
                NavigateRecords(ds);
            }
            MessageBox.Show("No More Rows");
        }
    }

    private void btnPrevious_Click(object sender, EventArgs e)
    {
        if (inc > 0)
        {
           inc= inc-1;
           NavigateRecords(ds);
        }
        else
        {
            if (inc != 0)
            {
                inc = 0;
                NavigateRecords(ds);
            }
            MessageBox.Show("First Record");
        }
    }

    private void btnLast_Click(object sender, EventArgs e)
    {
        if (inc != MaxRows - 1)
        {
            inc = MaxRows - 1;
            NavigateRecords(ds);
        }
    }

    private void btnFirst_Click(object sender, EventArgs e)
    {
        if (inc != 0)
        {
            inc = 0;
            NavigateRecords(ds);
        }
    }

Posted 11-Jul-15 9:06am

Member 11341510

Updated 11-Jul-15 9:54am

Wendelius

v6

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Wendelius · Accepted Answer · 2015-07-11T09:39:00

Solution 1

From the code you have provided as far as I can see you don't populate the dataset anywhere. You do set the SQL statement and the connection and so on but I can't find a call to Fill[^] method anywhere. If this is true there's no data fetched from the database thus leaving your data row non existent.

Posted 11-Jul-15 9:39am

Wendelius

Comments

Member 11341510 11-Jul-15 15:43pm

I have used a separate class for it:
using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace testNavData
{
class DatabaseConnection
{
private string sql_String;
private string strCon;
System.Data.SqlClient.SqlDataAdapter da_1;

public string Sql
{
set { sql_String = value; }
}

public string connection_string
{
set { strCon = value; }

}
public System.Data.DataSet GetConnection
{
get { return MyDataSet(); }
}
private System.Data.DataSet MyDataSet()
{
System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(strCon);
con.Open();
da_1 = new System.Data.SqlClient.SqlDataAdapter(sql_String, con);
System.Data.DataSet dat_set = new System.Data.DataSet();
da_1.Fill(dat_set, "Table_Data_1");
con.Close();
return dat_set;
}
public void UpdateDatabase(System.Data.DataSet ds)
{
System.Data.SqlClient.SqlCommandBuilder cb = new SqlCommandBuilder(da_1);
cb.DataAdapter.Update(ds.Tables[0]);
}
}

}
Also I rephrased the question...If u can please check once...

Wendelius 11-Jul-15 15:49pm

If you debug the program, what is the value of the MaxRows in
MaxRows = ds.Tables[0].Rows.Count;

Member 11341510 11-Jul-15 15:53pm

5(I have 5 records so the value is correct)

Wendelius 11-Jul-15 15:56pm

Is the error occurring on this row:

dRow = ds.Tables[0].Rows[inc];

If it is, place a breakpoint on that row and check, what is the value of inc If the error occurs on later rows, still check the value of inc.

Member 11341510 11-Jul-15 15:55pm

The first time the NavigateRecords function is working fine and the textboxes are populated. I think it has to do with the scope of ds dataset arguement that is passed. But don't know how to solve it.

Wendelius 11-Jul-15 15:59pm

That's true, you actually use different dataset in constructor.

So instead of having

private void Form1_Load(object sender, EventArgs e)
{
DataSet ds=new DataSet();
String SQ;

modify it to

private void Form1_Load(object sender, EventArgs e)
{
this.ds=new DataSet();
String SQ;

This should populate the dataset that is defined on form level.

Member 11341510 11-Jul-15 15:59pm

yes the error is occuring on that line itself.

Member 11341510 11-Jul-15 16:03pm

Wow...it's working fine now. Can you please expain how 'this' works

Wendelius 11-Jul-15 16:06pm

You actually don't necessarily need this. I just added it for clarity.

this refers to the window object and ensures that you're using the variable from 'correct scope'. The problem was that in the constructor you actually created a new ds variable with the scope of constructor only. You filled this variable but the one defined at module level remain empty thus causing the problem.

Hope this clarifies the situation :)

Member 11341510 11-Jul-15 16:13pm

Yes...Thank u a ton for your guidance :)

Wendelius 11-Jul-15 16:17pm

You're most welcome :)

Member 11341510 12-Jul-15 0:30am

There is one more thing I am not clear about. How to work this out in the above code...
MessageBox.Show(objConnect.Sql);

Wendelius 12-Jul-15 3:09am

Based on the error message (property lacks get accessor) it only has a setter so you'd need to implement get in order to get the SQL statement from the property.

Have a look at https://msdn.microsoft.com/en-us/library/ms228503.aspx[^]