插入数据库后，从另一种形式更新组合框中的值

Question

Can i know why am i getting weird output whereby the combobox does not refresh and show new values when a value is added to database from another form. Below my sample code

This is form code where the combobox need to be updated

public partial class Form1 : Form
{
    OleDbConnection con = new OleDbConnection("Provider=MSDAORA;Data Source=orcl;User ID=nareen1093;Password=nareen1093;Unicode=True");

    public Form1()
    {
        InitializeComponent();
        loadButton();
    }

    public void loadButton ()
    {
        con.Open();
        OleDbDataAdapter oda = new OleDbDataAdapter("select serial_number from fingerprint_device where serial_number like '%'", con);
        DataTable dt = new DataTable();
        oda.Fill(dt);
        comboBox1.DataSource = dt;
        comboBox1.DisplayMember = "serial_number";
        comboBox1.SelectedIndex = -1;
        con.Close();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        Form2 form2 = new Form2();
        form2.ShowDialog();
    }
}

this is form2 where the insert into database takes place.

public partial class Form2 : Form
{
    OleDbConnection con = new OleDbConnection("Provider=MSDAORA;Data Source=orcl;User ID=nareen1093;Password=nareen1093;Unicode=True");

    public Form2()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        con.Open();

        try
        {
            OleDbCommand cmd = new OleDbCommand("insert into fingerprint_device values ('" + textBox1.Text + "','" + textBox2.Text + "','" + textBox3.Text + "')", con);
            cmd.ExecuteNonQuery();
            MessageBox.Show("Registration Success", "Status", MessageBoxButtons.OK, MessageBoxIcon.Information);
            con.Close();
            Form1 form1 = new Form1();
            form1.loadButton();

        }

        catch (Exception ex)
        {
            MessageBox.Show(ex + "", "Status", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }

        finally
        {
            con.Close();
        }
    }
}

Answer 1

You are doing couple of things that cause the problem.

First Problem

In your Form2 button click you create a NEW form, call loadButton of this INSTANCE and close Form2. So, any changes made to Form2 is gone now. This happens as execution of form2.ShowDialog(); finishes. So, you have updated your comboBox, but update happened on a new instance of Form1, and it is disposed without showing the result.

Second Problem

You are adding new values to DB on Form2, but you haven't updated your combo in Form1. Since new instance of Form1 created in Form2 is disposed(refer to First Problem), again, comboBox control in current instance of Form1 is not updated.

Solution

Remove Form1 form1 = new Form1(); and form1.loadButton(); from Form2 button1_Click . Now add loadButton() after form2.ShowDialog();

Now, when Form2 is closed your loadButton() will execute and update combo.

public partial class Form1 : Form
{
OleDbConnection con = new OleDbConnection("Provider=MSDAORA;Data Source=orcl;User ID=nareen1093;Password=nareen1093;Unicode=True");

public Form1()
{
    InitializeComponent();
    loadButton();
}

public void loadButton ()
{
    con.Open();
    OleDbDataAdapter oda = new OleDbDataAdapter("select serial_number from fingerprint_device where serial_number like '%'", con);
    DataTable dt = new DataTable();
    oda.Fill(dt);
    comboBox1.DataSource = dt;
    comboBox1.DisplayMember = "serial_number";
    comboBox1.SelectedIndex = -1;
    con.Close();
}

private void button1_Click(object sender, EventArgs e)
{
    Form2 form2 = new Form2();
    form2.ShowDialog();
    loadButton();
}
}

public partial class Form2 : Form
{
OleDbConnection con = new OleDbConnection("Provider=MSDAORA;Data Source=orcl;User ID=nareen1093;Password=nareen1093;Unicode=True");

public Form2()
{
    InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
    con.Open();

    try
    {
        OleDbCommand cmd = new OleDbCommand("insert into fingerprint_device values ('" + textBox1.Text + "','" + textBox2.Text + "','" + textBox3.Text + "')", con);
        cmd.ExecuteNonQuery();
        MessageBox.Show("Registration Success", "Status", MessageBoxButtons.OK, MessageBoxIcon.Information);
        con.Close();

    }

    catch (Exception ex)
    {
        MessageBox.Show(ex + "", "Status", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }

    finally
    {
        con.Close();
    }
}
}