Re: How to access multiple controls thread safe in Windows Forms - C# Discussion Boards

Re: How to access multiple controls thread safe in Windows Forms

3-Oct-10 17:28

Many examples explains thread safe access over a single control,like updating a text of a
button or label etc.,How to change properties of multiple controls of a Form in thread safe manner.

private Thread CheckStatusThread = null;
public delegate void CheckStatusDelegate(int Count);
public CheckStatusDelegate CheckStatusHandler;

public Form1()
{
   InitializeComponent();
   CheckStatusThread = new Thread(new ThreadStart(CheckStatusThreadFunc));
   CheckStatusHandler = new CheckStatusDelegate(CheckPowerStatus);
}
private void Form1_Load(object sender, EventArgs e)
{
   CheckStatusThread.Start();
}   
public void CheckStatusThreadFunc()
{            
   int Cnt = 1;
   while (true)
   {
      this.Invoke(CheckStatusHandler,new object []{Cnt});//executed in Form1's own thread(?)
      Cnt++;
      Thread.Sleep(500);
   }
}

public void CheckPowerStatus(int Count)
{
   int Cnt=Count;            
                            
   //Update 3 controls properties
   StatusBarLabel1.Text = "Checking PowerStatus " + Cnt;                 
   dataGridView1.Rows[2].Cells[4].Value = Cnt;
   label1.Text = Convert.ToString("Cnt "+Cnt);                  
}

The CheckPowerStatus function change properties of 3 controls in Form1.
Do I need to use 3 delegates to update each control on 3 different functions.
Or the above code is thread safe?

Mycroft Holmes3-Oct-10 17:45

Mycroft Holmes

3-Oct-10 17:45

All threading issues get referred to Luc - see his articles[^] here.

Never underestimate the power of human stupidity
RAH

Re: How to access multiple controls thread safe in Windows Forms

Luc Pattyn3-Oct-10 17:49

Re: How to access multiple controls thread safe in Windows Forms

3-Oct-10 17:49

Interesting link.

Rose | [Rose]

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Luc Pattyn3-Oct-10 17:48

Re: How to access multiple controls thread safe in Windows Forms

3-Oct-10 17:48

you're not allowed to touch a Control from a random thread, so yes you need one or more Invoke calls. The proper way to handle simultaneous Control updates is by stuffing all the data you need in a little suitcase (i.e. a little class) and invoke once, let the delegate unpack the suitcase and do whatever needs to be done to the GUI. Assuming all GUI Controls got created on the main thread, all those Control.Invoke calls are equivalent anyhow, they all send the delegate to the main thread, no matter what they do to which Control.

This[^] article of mine explains the basics, you may know most of it already.

Smile | :)

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poda3-Oct-10 21:08

Re: How to access multiple controls thread safe in Windows Forms

3-Oct-10 21:08

In article, you suggest to use Control and the property as generic parameter.
But Control is the base class.The common property is only Text for all controls.
But in case of specific properties of a control,how can use generic method.

Suppose DataGridView.Rows[2].Cells[3].Value-how can use Control?
Because Control.Rows does not exists.

So if I need to update or access 3 controls 2 properties,
then have to write 6 delegates and 6 functions to do the job?

Luc Pattyn4-Oct-10 1:32

Re: How to access multiple controls thread safe in Windows Forms

4-Oct-10 1:32

Actually I already answered that; here is one way:

// the anonymous form (C# consumer)
public void SetCount(int count) {
    dataGridView1.Invoke(new MethodInvoker(delegate() {
       StatusBarLabel1.Text = "Checking PowerStatus " + count;                 
       dataGridView1.Rows[2].Cells[4].Value = count;
       label1.Text = Convert.ToString("Cnt "+count);                  
    }));
}

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poda4-Oct-10 5:40

Re: How to access multiple controls thread safe in Windows Forms

4-Oct-10 5:40

Thanks for your replies Luc Pattyn.

Here you only use dataGridView1.Invoke,
but update other controls also.Is that ok?

Luc Pattyn4-Oct-10 5:55

Re: How to access multiple controls thread safe in Windows Forms

4-Oct-10 5:55

poda wrote:
Is that ok?

Yes. I told you before:

all those Control.Invoke calls are equivalent anyhow, they all send the delegate to the main thread, no matter what they do to which Control.

And you're welcome.

Smile | :)

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#realJSOP4-Oct-10 2:03

#realJSOP

4-Oct-10 2:03

Required reading, if you ask me. Smile | :)

.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
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Re: How to access multiple controls thread safe in Windows Forms

poda4-Oct-10 5:42

4-Oct-10 5:42

Would you please kindly refer me some links.

Message Filter

electriac3-Oct-10 11:37

electriac

3-Oct-10 11:37

I do not understand why this will not compile. I have used it in other programs but I must be missing something here.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace mfwmp
{
    public partial class Form1 : Form, IMessageFilter
    {
        public Form1()
        {
            InitializeComponent();
            Application.AddMessageFilter(this);
        }
    }
}
//Error	1	'mfwmp.Form1' does not implement interface member //'System.Windows.Forms.IMessageFilter.PreFilterMessage(ref System.Windows.Forms.Message)'

Henry Minute3-Oct-10 11:49

Henry Minute

3-Oct-10 11:49

Well the PreFilterMessage() Method has been part of the interface since at least .Net 1.1.

It would be a pretty weird interface if it had no methods or properties.

Henry Minute

Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”

Dave Kreskowiak3-Oct-10 11:58

Dave Kreskowiak

3-Oct-10 11:58

Read the error message. You created a class that inherits from Form and IMessageFilter, but you never provided an implementation for IMessageFilter.PreFilterMessage(...).

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

electriac3-Oct-10 12:03

electriac

3-Oct-10 12:03

Thanks got it fixed with your help. Stupid me. I assumed the minimal code should have compiled.

Luc Pattyn3-Oct-10 12:03

3-Oct-10 12:03

Hi George,

electriac wrote:
public partial class Form1 : Form, IMessageFilter

when you promise to implement some interface, you must do so. Hence:
- either drop the IMessageFilter in that line;
- or provide all its members; that would be bool PreFilterMessage(ref Message m) { ... }

Cheers,

Luc

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Yield break

Brij3-Oct-10 8:12

Brij

3-Oct-10 8:12

Hi all,

I was learning yield operator. And made a function like this.

public IEnumerable<Guid> GetIds(int count, DateTime time)
        {
            
            Console.WriteLine("Start");
            {
                if (DateTime.Now > time)
                    yield break;
                else
                    yield return Guid.NewGuid();
            }
            Console.WriteLine("End");
        }

But End never get printed.Can anyone tell why? Because after break statement it should get out of the loop and print it.

Cheers!!
Brij
My Blog:http://brijbhushan.wordpress.com

Check my latest Article :ViewState - Various ways to reduce performance overhead

harold aptroot3-Oct-10 8:48

harold aptroot

3-Oct-10 8:48

(what loop?)

yield break does not break out of a loop, it "signals the end of the iterator", or as msdn also says:
"In a yield break statement, control is unconditionally returned to the caller of the iterator"
Source: http://msdn.microsoft.com/en-us/library/9k7k7cf0.aspx[^]

Henry Minute3-Oct-10 8:56

Henry Minute

3-Oct-10 8:56

From the relevant MSDN page for break:

The break statement terminates the closest enclosing loop or switch statement in which it appears. Control is passed to the statement that follows the terminated statement, if any.

So break breaks out of loops and switch statements. I am guessing that in this case it breaks out of your method.

Same for yield:

Used in an iterator block to provide a value to the enumerator object or to signal the end of iteration.

Once again yield is meant to be used in an iteration. if is not strictly speaking an iteration, although I suspect that your else block would run.

The pages I looked at did not say what these statements do when not used in iterations.

PIEBALDconsult3-Oct-10 8:58

PIEBALDconsult

3-Oct-10 8:58

Because you terminate the method before you get there.

Brij3-Oct-10 9:15

Brij

3-Oct-10 9:15

Thanks to all for answers.

I got the point. Whenever we write yield it returns IEnumerable to the caller.And once yield statement get executed, no statements get executed.

Thanks again..

Cheers!!
Brij
My Blog:http://brijbhushan.wordpress.com

Check my latest Article :ViewState - Various ways to reduce performance overhead

Pete O'Hanlon3-Oct-10 9:21

Pete O'Hanlon

3-Oct-10 9:21

One thing - when you built the code, did it not warn you that an unreachable condition had been detected? It's important to pay attention to warnings as well.

I have CDO, it's OCD with the letters in the right order; just as they ruddy well should be

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Brij3-Oct-10 9:28

Brij

3-Oct-10 9:28

Pete O'Hanlon wrote:
did it not warn you that an unreachable condition had been detected?

I am using VS2008 and there was no warning.

Cheers!!
Brij
My Blog:http://brijbhushan.wordpress.com

Check my latest Article :ViewState - Various ways to reduce performance overhead