当我按下取消按钮时，以表格2显示消息框

我有三种形式的winform应用程序。其中form3有两个buton和一些文本框。我想知道为什么我的表格显示一个名为"；重复"；当我按下表格的取消按钮时。

事实上，我告诉3号表格取消并返回1号表格。它完成了任务。但在来到表格1之前，它向我显示了一个消息框"；重复"；我不想看到。

如何避免此弹出窗口？

表单3中的代码

   private void submit_Click(object sender, EventArgs e)
    {
        // this button click event handler will raise the 
        // event which can then intercepted by any listeners
    //some codes....
        this.Dispose();
    }
private void cancel_Click(object sender, EventArgs e)
    {
        this.Close();
    }

表单1中的代码

private void btn_open_form3_Click(object sender, EventArgs e)
    {
        Form3 f = new Form3();
        string l = "true";
        // Add an event handler to update this form
        // when the address form is updated (when AddressUpdated fires).
        f.AddressUpdated += new Form3.AddressUpdateHandler(AddressForm_ButtonClicked);
        f.ShowDialog();
        if (String.IsNullOrEmpty(file_NameTextBox.Text.ToString()))
        {
            frmShowMessage.Show("Try again!!!", "Missing!!!!", enumMessageIcon.Error, enumMessageButton.OK);
            //cell_check();
        }
        else
        {
            if (checkexistornot())
            {
                if (file_NameTextBox.Text == string.Empty)
                {
                    cell_check();
                }
                else
                {
                    SqlConnection con = new SqlConnection(@"Data Source=DVSQL'SQLEXPRESS;Initial Catalog=CncDB;Persist Security Info=True;User ID=CncDbUser;Password=*****");
                    con.Open();
                    SqlCommand cmd = new SqlCommand(@"INSERT INTO cncinfo (part,drawings,draftpath,comments) VALUES ('" + file_NameTextBox.Text + "','" + drawingsTextBox.Text + "','" + gcodeTextBox.Text + "','" + commentsTextBox.Text + "') ", con);
                    cmd.ExecuteNonQuery();
                    con.Close();
                    load_table();
                }
            }
        }
    }
    private void AddressForm_ButtonClicked(object sender, AddressUpdateEventArgs e)
    {
        // update the forms values from the event args
        file_NameTextBox.Text = e.File_Name;
        drawingsTextBox.Text = e.Drawings;
        gcodeTextBox.Text = e.Gcode;
        commentsTextBox.Text = e.Comments;
    }
    public bool checkexistornot()
    {
        SqlConnection con = new SqlConnection(@"Data Source=DVSQL'SQLEXPRESS;Initial Catalog=CncDB;User ID=CncDbUser;password=*****");
        con.Open();
        SqlCommand cmd = new SqlCommand("select part from cncinfo where part='" + this.file_NameTextBox.Text + "'  ;", con);
        cmd.CommandType = CommandType.Text;
        cmd.Parameters.Add("@part", SqlDbType.NVarChar).Value = Convert.ToString(dataGridView1.Rows[0].Cells["Part Number"].Value);
        object obj = cmd.ExecuteScalar();
        cmd.ExecuteNonQuery();
        con.Close();
        if (obj!=null)
        {
            frmShowMessage.Show(""Duplicate!!!!", enumMessageIcon.Warning, enumMessageButton.OK);//- - - ->>showing this line if i press the cancel_Click from FORM3
            cell_check();
            return false;
        }
        else  
            return true;
    }

private void cancel_Click(object sender, EventArgs e)
{
    this.DialogResult = DialogResult.Cancel;
    this.Close();
}

if (f.DialogResult == DialogResult.Cancel)
{
    return;
}