How do I re-access the usercontrol that i've been declared before in a child control?

Question

I want to reaccess some of my child usercontrol from my main form..I want to access the object "watch" that i've declared from WatchListUC watch = new WatchListUC();

from my main I've declared this user control on a panel of the main form

 private void MyList_Load(object sender, EventArgs e)
    {
        LogInScreen screen = new LogInScreen();
        panel2.Controls.Clear();
        panel2.Controls.Add(screen);
        loadDB();
        grid.ContextMenuStrip = OpenDetails;

    }

then after that i created a login and there i was able to call the WatchListUC watch = new WatchListUC(); which i want to recall later

on the login screen here's the code

private void LogIn_Click(object sender, EventArgs e)
    {
        SuspendLayout();
        try
        {
            MySqlConnection conn = new MySqlConnection(myConnection);
            conn.Open();
            MySqlCommand command = new MySqlCommand("SELECT * FROM maindatabase.users where user=?parameter1 and pass=?parameter2;", conn);
            command.Parameters.AddWithValue("?parameter1", User.Text);
            command.Parameters.AddWithValue("?parameter2", Pass.Text);
            MySqlDataReader reader = command.ExecuteReader();

            int ctr = 0;
            while (reader.Read())
            {
                ctr++;
               // controlnum = reader["idnum"].ToString();
                MyList.AccountControlNum = int.Parse(reader["idnum"].ToString());
               // MessageBox.Show(MyList.AccountControlNum.ToString());
            }
            if (ctr == 1)
            {
                this.Parent.Controls.Remove(this);
                MyList my = MyList.ActiveForm as MyList;
                UserAccount acc = new UserAccount();
                my.panel2.Controls.Add(acc);
                my.label1.Text = reader["user"].ToString()+" 'List";
                WatchListUC watch = new WatchListUC();
                my.panel3.Controls.Clear();
                my.panel3.Controls.Add(watch);
                FinishListUC finish = new FinishListUC();
                my.panel4.Controls.Clear();
                my.panel4.Controls.Add(finish);
              //  MessageBox.Show("Success!");
            }
            else
            {
                MessageBox.Show("Invalid Username or Password!");
            }

            conn.Close();
            ResumeLayout();
        }
        catch (Exception ex)
        {
            MessageBox.Show("error" + ex);
            ResumeLayout();
        }
        ResumeLayout();
    }

now on my main form how I do I reaccess here after the "insertWL()" method??

void ConfirmedWL()
    {
        SuspendLayout();
        try
        {
            MySqlConnection conn = new MySqlConnection(myConnection);
            conn.Open();
            MySqlCommand command = new MySqlCommand("SELECT * FROM maindatabase.watchlist where ControlNum=?CN and idnum=?ID;", conn);
            command.Parameters.AddWithValue("?CN", int.Parse(a.ToString()));
            command.Parameters.AddWithValue("?ID", MyList.AccountControlNum);
            MySqlDataReader reader = command.ExecuteReader();

            int ctr = 0;
            while (reader.Read())
            {
                ctr++;

            }
            if (ctr == 1)
            {
                MessageBox.Show("Already Existed!");
            }
            else
            {
                insertWL();                    
                //WatchListUC watch1 = panel3.Controls.Find("watch", true).DefaultIfEmpty() as WatchListUC;
                //watch1.dvgRefresh();

              //here i want to recall the watch so i can call the method dvgRefresh();
            }


            conn.Close();
            ResumeLayout();
        }
        catch { }
    }<br>

I was hoping someone could help me here's my full code and screen shots http://www.mediafire.com/download/1l18e6v8158mi16/Help_please.rar

Answer 1

So if I've understood you correctly, you create your WatchListUC (UserControl) inside of a panel that is on your main form? What I'm confused about is where is this login code located? Is that also inside of your main form?

Main Form
   | - Panel
        | - WatchListUC

As long as you're creating WatchListUC from code inside of your main form, all you need to do is save it to a variable that is outside the scope of your method.

Answer 2

UserControl are visual objects, and can be used like every object.

That means that you can store their references in any variable within the scope that fits the best for you.

In your example, I would define watch at the Form level:

WatchListUC watch;

Then, in the LogIn_Click event method, there is nothing wrong doing this:

watch = new WatchListUC();
my.panel3.Controls.Clear();
my.panel3.Controls.Add(watch);

Finally, in the ConfirmedWL method, just use the watch instance you have.

...
else
{
    insertWL();                    
    watch.dvgRefresh();
}

The drawback of this approach is that you have to be careful about your control lifecycle:

• watch will be null if it is not instantiated, and this can lead to NullReferenceException if you try to use it without putting a new control inside it.
• Also, remember to call .Dispose() on the controls you created on the fly when you are finished with them. This is not required if you plan to have only one instance of WatchListUC during your application life cycle.