C# Discussion Boards - CodeProject

Re: Regarding calling Event

26-Dec-05 23:28

Events by convention take two parameters, object sender and System.EventArgs e. The sender tells you from where the event has been fired, and the eventargs is a reference to a class where you can define your entry and exit parameters for the event. You can derive a new class from EventArgs for this where necessary, although in your example you're in the realm where everything has been defined for you, so you really shouldn't be doing this.

Alternatively, if you want to break with convention and best practices you can define your own events which don't follow this pattern, but you won't be able to attach these to things like the button click event, as it expects this sender/arguments prototype.

You can do this by defining a delegate which describes your callback prototype, and then creating an event of type said delegate.

I'd stick with convention if I were you...

Regards,
Rob Philpott.

peshkunta27-Dec-05 3:28

peshkunta

27-Dec-05 3:28

Alternatively you can do:

this.button1.Click += new System.EventHandler(this.button1_Click);

private void button1_Click(object sender, System.EventArgs e)
{
demo();
}

private int demo()
{
MessageBox.Show("Called");
return;

}

//OR

this.button1.Click += new System.EventHandler(this.button1_Click);

private void button1_Click(object sender, System.EventArgs e)
{
MessageBox.Show("Called");
return;
}

-- Don't worry about the world coming to an end today. It's already tomorrow in Australia --

problem displaying text in a textBox

zt.Prog26-Dec-05 23:03

26-Dec-05 23:03

I have an application with a form and a class.

The form has a textbox, and it creates an instance of the class when it loads.
In the class there is a thread that, let's say, calculates a number, and wants to display this number in the textbox on the form.

How can I do this?
(I can't seem to get access to the textbox from the class)

Rob Philpott26-Dec-05 23:15

26-Dec-05 23:15

Your textbox belongs to a class as well, the form class and by default this textbox has private access so you can't get at it.

Take a step back though, what you are trying to do here is tightly couple the GUI to the logic. You end up with a calculation class which can only be used in conjunction with a particular form. You should call out from the form class to the calculation class, collect the answer in the form class and then assign it to the textbox. The calculation class should be made as reusable as possible and not have a clue about the GUI of the application it is to be used in.

You need to be particularly careful if using worker threads - these should not access GUI components without a thread switch provided by BeginInvoke.

Regards,
Rob Philpott.

zt.Prog26-Dec-05 23:34

26-Dec-05 23:34

Ok, about not calling a certain form in the class, I agree with you, but I have a problem with "collecting the answer in the form class and then assigning it to the textbox" as you said, because I have to change the text in the textbox everytime the thread calculates a new value for the number. how can I do this in the form? how can I know when to collect the number?

about the last sentence you wrote:
"You need to be particularly careful if using worker threads - these should not access GUI components without a thread switch provided by BeginInvoke."
I didn't understand what u meant.
I'm fairly new to C#, and to threads in particular..
if u could explain further..

The thread I wrote is like this (it actually reads data and then does some calculation)

public class classA
{
Thread ReadThreadProc;

classA() //constructor
{
ReadThreadProc = new Thread(new ThreadStart(OpticsReadThread));
ReadThreadProc.Name = "ReadThread";
ReadThreadProc.IsBackground = true;
ReadThreadProc.Start();
}

private void ReadThread()
{
while (true)
{
Receive();
}
}

public void Receive()
{
//function that handles what the thread reads...
}

public void CloseThread()
{
ReadThreadProc.Abort();
}
}

I don't know if this is called a worker thread...

hope I was clear. if u need any further explanations, let me know.

I'm really stuck here...
thanks Smile | :)

))

Rob Philpott26-Dec-05 23:47

26-Dec-05 23:47

Hi again,

Yes, that's a worker thread you are creating there. A worker thread is a thread which doesn't contain a message pump (ie. GUI message handler). It's not a simple subject but the golden rule is that only the thread which creates a control should access it. Your main thread creates the textbox, and only it should access it, so you need to do a BeginInvoke to switch from the worker thread to the main thread to do the update.

Firstly though, try to decouple the calculations class from the GUI completely. A nice way to do this would be instantiate your calculations class and register the forms interest in an update event it exposes. You can then get the calculations class to run its thread and it will notify the form class via events when it needs to update the GUI. In the forms event handler we will have our BeginInvoke thread switch to ensure the correct thread does the update and the job's a goodun.

Incidentally, I'm not sure about the use of Abort for terminating a thread - I think that's bad but need to check the correct way to do it.

There are some tricky concepts here - thread switching/delegates/events etc., so if I've lost you completely let me know and I'll bosh you together a sample app...

Regards,
Rob Philpott.

zt.Prog27-Dec-05 0:04

27-Dec-05 0:04

I don't undersatnd what u meant by: "In the forms event handler we will have our BeginInvoke thread switch to ensure the correct thread does the update and the job's a goodun."
what is BeginInvoke thread switch?
can u please write an example of code?

about the termination of the thread - I went by an example I found, and I'm also not sure it's the best way to end a thread. If u have any suggestions, they will be welcomed...

thanks Smile | :)

Rob Philpott27-Dec-05 0:18

27-Dec-05 0:18

Your app will have two threads in it - the primary thread which creates your form and control and then spends most of its life idling but handles button clicks and the like, and the worker thread which churns away in the background.

This worker thread wants to update the GUI but we can't allow this - this must be done by the primary thread. If you do the update on worker thread all will seem well and then one day your program will hang and your life goes down the toilet. This is where BeginInvoke comes in, the worker thread calls this to get the primary thread to do the update for it. I'm not 100% on this but I think it does a PostMessage under the covers.

I'll put a sample together and email it to you. Are you using VS2003 or VS2005? Incidentally, I understand that VS2005 complains if you attempt to update the GUI from the worker thread - this is not the case in 2003.

Regards,
Rob Philpott.

zt.Prog27-Dec-05 1:25

27-Dec-05 1:25

I'm using VS2005 beta version..

cbhkenshin27-Dec-05 0:19

cbhkenshin

27-Dec-05 0:19

Will for just an easy way to get access to the text box in simple thoughts

you just have to go to the Form Designer Code And Then change

private System.Windows.Forms.TextBox textBox1;

to

public static System.Windows.Forms.TextBox textBox1;

and also change all

this.textBox1....etc

to

Form1.textBox1....etc

and then you can control the textbox from the class or any where...;D

public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
}

class testing_textbxx
{
int a;

public void change()
{
Form1.textBox1.Text = "This is a good way for Solving";
}
}

Rob Philpott27-Dec-05 0:37