Accessing form components from Thread

[Umair.P]

Hi all,
I am trying to write a software where I want to put some UI in the form that would indicate the loading process(progress bar, loading image etc).
Please advice how to do it since when a form runs some code all the form gets static. Threading is also not helping either

[LizR]

You have to update components by calling them with pinvoke - theres some great examples that come in your helpfile

[Umair.P]

I know nothing abt PInvoke. I searched the net and All I get is that it is used to include functionality of different dlls.

how is going to solve my problem.

[dickersonka]

LizR you sure you are meaning pinvoke?

i do it by invokerequired

this example here, is setting a button enabled

private delegate void UpdateBtnContinueDelegate();
        private void UpdateBtnContinue()
        {
            if (this.InvokeRequired)
            {
                UpdateBtnContinueDelegate updateCount = new UpdateBtnContinueDelegate(this.UpdateBtnContinue);
                this.Invoke(updateCount);
            }
            else
            {
                this.btnContinue.Text = "Continue";
                this.btnContinue.Enabled = true;
            }
        }

from your code you would just call UpdateBtnContinue() and let the method take care of the invoke

[Umair.P]

I think I have been unable to eleborate the problem.

I want to load a combo box from a data base. Now, when I make a connection to the data base and retrieve the data, it takes time. and in that time the form remains statix and gives a look of hanged application. I want to overcome this. I want the form to display some sort of progress but its not working that way. I am unable to use thread since it does not allow to access form components and load them with value or alter their properties.

[dickersonka]

the concept is right, i gave you an example with a button, you can do the same with a progress bar

this assumes you have progressbar name pbStatus

private delegate void UpdatePbDelegate();
        private void UpdatePb()
        {
            if (this.pbStatus.InvokeRequired)
            {
                UpdatePbDelegate updateCount = new UpdatePbDelegate(this.UpdatePb);
                this.pbStatus.Invoke(updateCount);
            }
            else
            {
                if(this.pbStatus.Value == 100)
		{
			this.pbStatus.Value = 1;
		}
                this.pbStatus.PerformStep();
                this.pbStatus.Refresh();
            }
        }

[dickersonka]

sorry forgot the thread part

private void DownloadData()
{
//your code in here that downloads your values
}

private void GetDropDownValues()
{
 Thread t= new Thread(new ThreadStart(DownloadData));
            t.Start();

            while (t.IsAlive)
            {
                UpdatePb();
                System.Threading.Thread.Sleep(50);
            }
}

also, i wouldn't recommend it, but you can call UpdatePb() from anywhere in the code, because it will invoke itself if it is a cross thread call

[LizR]

LizR you sure you are meaning pinvoke?

Darn it, its what comes when Im mid code and doing something else .. (and then go out to do something) sigh - see previous version where I kept saying textbox not textbook.. :(

Yes, I meant invoke. The silly part is, if you try calling the UI from a thread, it would have told you in the helpfile what to do when it crashed..

[dickersonka]

Lol lizr i saw your textbox comment the other day, and thought you must have been a little preoccupied.

Ans as Lizr said, its in the helpfile along with the example i gave you.

[Jugortha]

To avoid the problem of Form freezing you can use the asynchrone mode to load data from the data base

using System;
using System.Data;
using System.Threading;
using System.Data.SqlClient;

class MainClass {
    public static void CallbackHandler(IAsyncResult result) {
        using (SqlCommand cmd = result.AsyncState as SqlCommand) {
            using (SqlDataReader reader = cmd.EndExecuteReader(result)) {
                lock (Console.Out) {
                    while (reader.Read()) {
                        Console.WriteLine("  {0} = {1}",
                            reader["ID"],
                            reader["FirstName"]);
                    }
                }
            }
        }
    }

    public static void Main()
    {
        using (SqlConnection con = new SqlConnection())
        {
            con.ConnectionString = "server=(local)\\SQLEXPRESS;database=MyDatabase;Integrated Security=SSPI;Asynchronous Processing=true;";

            SqlCommand cmd = con.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "SELECT ID, FirstName FROM Employee";

            con.Open();
            cmd.BeginExecuteReader(CallbackHandler, cmd);

            // Continue with other processing.
            for (int count = 0; count < 10; count++)
            {
                lock (Console.Out)
                {
                    Console.WriteLine("{0} : Continue processing...",
                        DateTime.Now.ToString("HH:mm:ss.ffff"));
                }
                Thread.Sleep(500);
            }
        }
    }
}