Programming Forums > Application Development > C#

Jarod Silverstar · Sep 15th, 2007, 10:35 PM

Hi,
Got a little issue I am scratching my head over. In a program I am working on, I have a place where I have some basic output being writen to a window and what to have each line show up every second or so. But I can't see to get the timing to work.

I put together a little simple app to test some things, so maybe somebody could tell me why this is not working.

I start with one windows form, where a person enters a number and hits the button to call the next form.

(Toggle Plain Text)

private void btnDisplay_Click(object sender, EventArgs e)
        {
            int numItems = Convert.ToInt16(txtItems.Text);
            OutputList ost = new OutputList(numItems);

            ost.Show();
         }

The window that opens is simply a text box that I am writing lines to:

(Toggle Plain Text)

        public OutputList(int numItems)
        {
            InitializeComponent();
            int _numItems = numItems;

            int i = 0;
            string showItems;
            while (i < _numItems)
            {
                showItems = Convert.ToString("This is Item # " + i);
                txtListItem.Text += (showItems + "\r\n");
                Thread.Sleep(1000);
                i++;
            }
        }

But when I run this, the window opens after the number of seconds from the input and all the lines of text are already written.

I want the window to open first and then have each line of text written in it. Can I do it this way? Am I missing something simple? Or do I need to find another way of doing this?

Wizard1988 · Sep 15th, 2007, 10:43 PM

Try changing the parameter of Sleep()

Dameon · Sep 15th, 2007, 11:04 PM

The form is not shown until the ost.Show line. This does not happen until after the form is constructed. The form is not constructed until the list is fully populated, which takes a long time due to Thread.Sleep. You are probably looking to use a timer or background thread to add the list items after the form is already visible.

lectricpharaoh · Sep 15th, 2007, 11:17 PM

Your problem is that the UI runs on a single thread. This means event handlers too, such as the events that drive repainting of the controls. You set the control's text, then put the thread to sleep, so no updates happen. When the thread wakes up, it immediately proceeds to the next loop iteration (and thus is busy changing the control's text, and not updating the visual appearance). Once it's done updating the text (not the screen display of this text, mind you), you put it to sleep, and the cycle continues. In short, what is happening is that events are queued up, and handled in order. Until the event handler (btnDisplay_Click(), in this case) returns, no more events will be processed. If you've ever done any programming using the raw Win32 API, it's all driven by the 'message pump'; .NET thunks down to this within its guts.

A similar thing can be seen if you have a lengthy loop inside an event handler. Other events are deferred until the first one is handled.

Two good choices for resolving this would be to expose a property or method in your OutputList class whereby your regular class could update its display appropriately, or to have a timer in the OutputList class, and it could periodically update itself (you update txtListItem inside the timer tick event handler). Which is better really depends on what you're trying to do, and on whether OutputList will receive all necessary information in its constructor, or whether it needs periodic updating from another source (user, other form, database, whatever).

On a totally unrelated note, you might consider the TryParse() static method for converting primitive types; this allows you to avoid exception-handling semantics:

(Toggle Plain Text)

int value;
if(!int.TryParse(txtHopefullyItsANumber.Text, out value))
  MessageBox.Show("You must enter a valid number.", "Error");

[edit] What Dameon said, too. ;) [/edit]

Jarod Silverstar · Sep 16th, 2007, 4:20 PM

Thanks for the info, this explains what I was seeing.

I am still working on the actual program I am doing and was not sure if the thread.sleep method was going to be the best way of doing what I wanted anyway.

But it was still some good info. Just as long as I can remember this next time I run into the same situation, it was a worth while question.

Sep 15th, 2007, 10:35 PM	#1
Jarod Silverstar Newbie Join Date: Dec 2006 Posts: 7 Rep Power: 0	Thread.sleep issue Hi, Got a little issue I am scratching my head over. In a program I am working on, I have a place where I have some basic output being writen to a window and what to have each line show up every second or so. But I can't see to get the timing to work. I put together a little simple app to test some things, so maybe somebody could tell me why this is not working. I start with one windows form, where a person enters a number and hits the button to call the next form. (Toggle Plain Text) private void btnDisplay_Click(object sender, EventArgs e) { int numItems = Convert.ToInt16(txtItems.Text); OutputList ost = new OutputList(numItems); ost.Show(); } private void btnDisplay_Click(object sender, EventArgs e) { int numItems = Convert.ToInt16(txtItems.Text); OutputList ost = new OutputList(numItems); ost.Show(); } The window that opens is simply a text box that I am writing lines to: (Toggle Plain Text) public OutputList(int numItems) { InitializeComponent(); int _numItems = numItems; int i = 0; string showItems; while (i < _numItems) { showItems = Convert.ToString("This is Item # " + i); txtListItem.Text += (showItems + "\r\n"); Thread.Sleep(1000); i++; } } public OutputList(int numItems) { InitializeComponent(); int _numItems = numItems; int i = 0; string showItems; while (i < _numItems) { showItems = Convert.ToString("This is Item # " + i); txtListItem.Text += (showItems + "\r\n"); Thread.Sleep(1000); i++; } } But when I run this, the window opens after the number of seconds from the input and all the lines of text are already written. I want the window to open first and then have each line of text written in it. Can I do it this way? Am I missing something simple? Or do I need to find another way of doing this?

Sep 15th, 2007, 10:43 PM	#2
Wizard1988 Professional Programmer Join Date: Oct 2005 Location: Chitown Posts: 422 Rep Power: 4	Try changing the parameter of Sleep() __________________

Sep 15th, 2007, 11:04 PM	#3
Dameon Troll Join Date: Apr 2005 Location: Texas Posts: 732 Rep Power: 4	The form is not shown until the ost.Show line. This does not happen until after the form is constructed. The form is not constructed until the list is fully populated, which takes a long time due to Thread.Sleep. You are probably looking to use a timer or background thread to add the list items after the form is already visible. __________________ MD5(sig) = bcef75433db02e9ad9bf81d6f7c5c270

Sep 15th, 2007, 11:17 PM	#4
lectricpharaoh Caffeinated Neural Net Join Date: Jun 2005 Location: Wet west coast of Canada Posts: 1,122 Rep Power: 5	Your problem is that the UI runs on a single thread. This means event handlers too, such as the events that drive repainting of the controls. You set the control's text, then put the thread to sleep, so no updates happen. When the thread wakes up, it immediately proceeds to the next loop iteration (and thus is busy changing the control's text, and not updating the visual appearance). Once it's done updating the text (not the screen display of this text, mind you), you put it to sleep, and the cycle continues. In short, what is happening is that events are queued up, and handled in order. Until the event handler (btnDisplay_Click(), in this case) returns, no more events will be processed. If you've ever done any programming using the raw Win32 API, it's all driven by the 'message pump'; .NET thunks down to this within its guts. A similar thing can be seen if you have a lengthy loop inside an event handler. Other events are deferred until the first one is handled. Two good choices for resolving this would be to expose a property or method in your OutputList class whereby your regular class could update its display appropriately, or to have a timer in the OutputList class, and it could periodically update itself (you update txtListItem inside the timer tick event handler). Which is better really depends on what you're trying to do, and on whether OutputList will receive all necessary information in its constructor, or whether it needs periodic updating from another source (user, other form, database, whatever). On a totally unrelated note, you might consider the TryParse() static method for converting primitive types; this allows you to avoid exception-handling semantics: (Toggle Plain Text) int value; if(!int.TryParse(txtHopefullyItsANumber.Text, out value)) MessageBox.Show("You must enter a valid number.", "Error"); int value; if(!int.TryParse(txtHopefullyItsANumber.Text, out value)) MessageBox.Show("You must enter a valid number.", "Error"); [edit] What Dameon said, too. ;) [/edit] __________________ And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot. - Vaarsuvius, Order of the Stick

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Sep 16th, 2007, 4:20 PM	#5
Jarod Silverstar Newbie Join Date: Dec 2006 Posts: 7 Rep Power: 0	Thanks for the info, this explains what I was seeing. I am still working on the actual program I am doing and was not sure if the thread.sleep method was going to be the best way of doing what I wanted anyway. But it was still some good info. Just as long as I can remember this next time I run into the same situation, it was a worth while question.

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Thread.sleep issue