Database not accessible

praveen maurya

Hello There

I am just learning user Control in Visual Studio 2015. Everything was going fine but when i tried to access the database in user control file i am getting null error

the same connection string is working fine in winform but not working in usercontrol the error comming when I am trying to drag the user control page to my winform. the image of error is attached

my app.config code is written here

app.config

"1.0" encoding="utf-8" ?>
"CC" connectionString="Data Source=DESKTOP-M5IBRH0\sqlexpress;Initial Catalog=RMS;Integrated Security=True" providerName="System.Data.SqlClient"/>
"v4.0" sku=".NETFramework,Version=v4.5.2" />

Code of User Control:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Configuration;
namespace usercontrol_with_sqlconnection
{
public partial class user_A : UserControl
{
public static string constring = ConfigurationManager.ConnectionStrings["CC"].ConnectionString;
SqlConnection con = new SqlConnection(constring);
public user_A()
{
InitializeComponent();
}
}
}

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Jignesh Kumar6y ago
Accepted answer
Hi Praveen,

Please find below link, I would suggest to read from App.config file connection string.
https://social.msdn.microsoft.com/Forums/vstudio/en-US/d45e2126-4d38-40f8-ba5d-f578adcb8b7d/configurationmanagers-connectionstrings-null-in-user-control-project?forum=wpf
+1
praveen maurya6y ago
HI Jignesh

that article realy helps me to understand the basic.
but still i am not able to assign the string globaly in user control
i need to write under btn click event.

have you any suggestions how i can get the solution.
this code working perfectly
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Configuration;

namespace usercontrol_with_sqlconnection
{
    public partial class user_A : UserControl
    {
        public user_A()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection(Form1.constring);
            con.Open();
            string qry = "insert into login values('" + textBox1.Text + "','" + textBox2.Text + "', '" + textBox3.Text + "', '" + textBox4.Text + "')  ";
            SqlCommand sc = new SqlCommand(qry, con);
            int i = sc.ExecuteNonQuery();
            con.Close();
            if (i >= 1)
                MessageBox.Show("ITEM INSERTED SUCCESSFULLY", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
            else
                MessageBox.Show("SOMETHING WENT WRONG \n PLEASE CHECK", "Failed", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
}
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Rajanikant Hawaldar6y ago
It looks like your control is trying to establish a connection with a database on designtime, and the database cannot be found (probably because the designer tries to look in the Visual Studio bin directory). Your best bet is not to connect a database to a user control in design time, but dynamically link it during runtime. Wrap your user control load methods with: private void myUserControl_Load(object sender, EventArgs e) { if (!this.DesignMode) { //....stuff } }
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