ComboBox slow to populate with DataSource

Question

public class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

        Application.Run(new MainWindow());
    }
} 

class MainWindow : Form
{
    string[] list = new string[1548];
    TableLayoutPanel panel = new TableLayoutPanel();

    public MainWindow() : base()
    {
        Height = 2000;
        Width = 1000;

        Random rand = new Random();

        for (int i = 0; i < 1548; i++)
        {
            list[i] = rand.Next().ToString();
        }

        Button button = new Button();
        button.Text = "Press me";
        button.Click += Button_Click;

        panel.Controls.Add(button, 0, 0);

        panel.Height = 2000;
        panel.Width = 1000;

        Controls.Add(panel);

        Show();
    }

    private void Button_Click(object sender, EventArgs e)
    {
        for (int i = 0; i < 36; i++)
        {
            ComboBox box = new ComboBox();
            box.DataSource = list;

            panel.Controls.Add(box, 0, i+1);
        }
    }
}

This up here will create a window with a button and will pre-generate a list of 1548 random integers.

When you press the button 36 ComboBoxes will be created and populated with the pre-generated list. It will hang for a second or two.

Change it with box.Items.AddRange(list); and it will be even slower.

If you now comment line box.DataSource = list;, it will be significantly faster.

I don't understand why does it take so long to bind a data source to a comboBox. I'm guessing it has something to do with drawing the drop down menu.

Anyway, the comboBoxes I use in my program are all the same. They show the same list, but are binded to different "data slots" (they enable you to select an inventory item - list of items is same for every slot, but what is selected isn't).

Is there any way I can somehow force the program to draw only one ComboBox and use it for all 36? Od do something similar. Seems like a waste of resources to have it do same thing for 36 times...

It would speed up the startup time of the program.

user_7055665 · Answer

I don't understand why does it take so long to bind a data source to a comboBox. I'm guessing it has something to do with drawing the drop down menu.

I don't know how you have implemented your solution but it's not normal. What i firstly sugest you is to:

Create a loop with the number of combobox you want to display

for(x = 0; x < 36; x++)
{

}

Initialise your combobox and bind her, and finally store into an data structure

//intialize combobox
ComboBox cmb = new ComboBox();

//populate with a Datasource

List lstCmb = new List();

for(x = 0; x < 36; x++)
{
    // store controller into an data strucuture
    lstCmb.Add(cmb);
}

With all combobox pre-populated and loaded into that data struture you just need to use one of that 36 combobox's.

ComboBox slow to populate with DataSource

1 Answers