C# Discussion Boards - CodeProject

Russell Jones4-Apr-07 6:06

Russell Jones

4-Apr-07 6:06

I always make sure to dispose of Graphics objects as they have a bad habit of causing leaks if not thrown away after use.

liberal sprinklings of the using keyword don't hurt either.

Russ

HexaDeveloper4-Apr-07 7:44

4-Apr-07 7:44

hi ,

i draw alot of rectangles(one at each invalidate at a moment )

i draw in OnPaint but in it i cannot make dispose (what can i do)
also where i can use GC.Collect

Generator

Luc Pattyn4-Apr-07 11:06

4-Apr-07 11:06

Hi,

if you create some objects (a Pen, Brush or any other instance of a class that has
a public Dispose() method) inside your OnPaint method, you MUST call Dispose for them.

Additionally, if you need the same object over and over (such as new Pen(myColor)) then
I suggest you create it only once and keep it in a class member (rather than continuously
creating and disposing and collecting them).

And finally, if the objects you need correspond to system objects (such as the ones
available in SystemPens, SystemBrushes,...) I suggest you use these (without new,
without Dispose !).

And I do not recommend you call GC.Collect at all (the gc works fine all by itself),
and certainly not from inside any OnPaint method ! (GC.Collect is expensive and
should not be called by the UI thread, it might ruin the responsiveness).

Smile | :)

Luc Pattyn

[My Articles]

HexaDeveloper8-Apr-07 5:49

8-Apr-07 5:49

Hi,

from debug of my program i noticed that Update();
is making bad effect and may be the reason of memory leak

so can any one tell me what is the disadvantages of it

thanx

Generator

Luc Pattyn8-Apr-07 6:37

8-Apr-07 6:37

Hi,

if you mean Control.Update() I dont know why you think you need it. In all the programs
I have ever developed I never felt the need for it: correct program design (including
the use of background threads for longwinding tasks) results in good responsiveness
without problems.

On the other hand, Update does NOT cause memory leaks; only errors in your code
( or in .NET itself, rather unlikely) can do that, e.g. not calling Dispose().

If you want us to be able to help you, you should explain more about your app,
and publish the pieces of code you suspect yourself, rather than using
obscure observations (a very big space of memory, unreachable code, bad effect).

Smile | :)

Luc Pattyn

[My Articles]

HexaDeveloper8-Apr-07 6:49

8-Apr-07 6:49

hi,
ok you are right i am making a packet that moved on a line
when i click a button and stopped when i click stop
so i use thread but the stop button be not responsive and the app hang up

so one here advice me to use BackgroundWorker so i use it but i have a very large consuming of memory when i click the first button i donot no why so i try to solve it hardly
so last i remove update then the memory consuming decreased but not every time i start my application run i work well
some times it work bad so i tried also

so to ask a question if i called a method for a thread or backgroundworker and in this method other method is called
the second method would be run by the program process or by this thread

if by program then i will correct my code

else
i will publish the pieces of code to see(i miss understanding)

thanx alot

Generator

Luc Pattyn8-Apr-07 7:08

8-Apr-07 7:08

Hi,

I did not understand very much of what you wrote.
It seems like you want some animation to start when a "Start" button is pressed,
and stopped when a "Stop" button is pressed, and furthermore the "Stop" button does
not (always) work reliably.

There can be several causes for this:
- you might be doing too much stuff in the UI thread
- CPU load might be high at or above the priority of the UI thread
- some logical error in the communication bewteen the "Stop" button handler,
and the thread that does the animation.

Maybe this info will help:

methods are executed on the same thread as the code that calls them (unless you
do very special things, such as calling Invoke). Some asynchronous stuff is executed
on another method automatically (e.g. a tick handler for all timers, except a
Windows.Forms.Timer).

if you try to modify the user interface (i.e. add/remove/modify a Control) from
a thread other than the UI thread (the one you have at start) then:
- under .NET 1.1 your program may freeze, or behave unpredictably
- under .NET 2.0/3.0 you will get some "CrossThread" Exception (you could set some
flag false to skip the checks, but then the app may freeze again).

You may want to create your own background thread, so you can fully control it
(set priority, kill/abort it, etc).

You may want to find and read an MSDN article entitled
"How to: Use a Background Thread to Search for Files "
which probably explains more on InvokeRequired, Invoke, threads, etc.

Smile | :)

Luc Pattyn

[My Articles]

HexaDeveloper8-Apr-07 7:12

Re: Memory leak [modified]

8-Apr-07 7:12

private void btn_simulate_Click(object sender, EventArgs e)<br />
        {<br />
            this.btn_simulate.Enabled = false;<br />
            this.btn_stop.Enabled = true;<br />
            closeThreadRequested = false;<br />
            if (!packetsMovingThread.IsBusy)<br />
                packetsMovingThread.RunWorkerAsync();<br />
            <br />
        }<br />
        /// <summary><br />
        /// When press the button stop simulation <br />
        /// </summary><br />
        private void btn_stop_Click(object sender, EventArgs e)<br />
        {<br />
            closeThreadRequested = true;<br />
            this.btn_stop.Enabled = false;<br />
            this.btn_simulate.Enabled = true;<br />
            if (packetsMovingThread.IsBusy)<br />
                packetsMovingThread.CancelAsync();<br />
        }<br />
        /// <summary><br />
        /// An event handler that called when thread of background task begin   <br />
        /// </summary><br />
        private void packetsMovingThread_DoWork(object sender, DoWorkEventArgs e)<br />
        {<br />
            BackgroundWorker worker = sender as BackgroundWorker;<br />
            if (worker.CancellationPending)<br />
                e.Cancel = true;<br />
            else<br />
                dataPacket.simulate(lineArray, closeThreadRequested, ref source_pnt,<br />
                    ref destination_pnt, packetsMovingThread);<br />
        }<br />
        /// <summary><br />
        /// An event handler that called when thread of background task Aborted<br />
        /// for any reason(Error,Cancel,Normal Completion)  <br />
        /// </summary><br />
        private void packetsMovingThread_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)<br />
        {<br />
            if (e.Error != null)<br />
                MessageBox.Show(e.Error.Message);<br />
            else if (e.Cancelled)<br />
                MessageBox.Show("Cancelled");<br />
        }<br />
        /// <summary><br />
        /// An event handler that called when thread of background task has changes in <br />
        /// its state or by calling ReportChanges() method<br />
        /// </summary><br />
        private void packetsMovingThread_ProgressChanged(object sender, ProgressChangedEventArgs e)<br />
        {<br />
            if (closeThreadRequested == false && !(source_pnt.IsEmpty))<br />
            {<br />
                dataPacket.drawPacket(this.CreateGraphics(), source_pnt);<br />
            }<br />
            Invalidate(drawingFrame);<br />
            // update here make bad effect on memory<br />
            //Update(); <br />
        }

public void drawPacket(Graphics grfx, Point location)<br />
     {<br />
         Pen pen = new Pen(type);<br />
         SolidBrush solidBrush = new SolidBrush(type);<br />
         grfx.DrawRectangle(pen, location.X, location.Y, 4, 4);<br />
         grfx.FillRectangle(solidBrush, location.X, location.Y, 4, 4);<br />
         pen.Dispose();<br />
         solidBrush.Dispose();<br />
     }

movePacket method compute next point and call
packetMovingThread(declared object).ReportProgress(100);

Generator

Luc Pattyn8-Apr-07 11:21

8-Apr-07 11:21

Hi,

your code contains this.CreateGraphics() which CREATES a Graphics, and hence
requires a matching Dispose() which is not present. I expect this is your main problem.

I dont see how exactly your backgroundworker is working, how iterations are achieved,
and how the drawing is handled by the UI thread; so there might be additional
causes for problems.

ADDED: drawing a packet should be part of your paint handler (so it gets called
whenever anything needs to be repainted, i.e. also when something that was temporarily
hiding your form gets removed, or when your app gets restored from being minimized);
your animation should just modify the parameters that control the drawing
(such as coordinates) and then make sure a repaint gets ordered (typiucally by
calling Invalidate).

Smile | :)

-- modified at 17:48 Sunday 8th April, 2007

Luc Pattyn

[My Articles]

HexaDeveloper8-Apr-07 12:43

8-Apr-07 12:43

hi Luc Pattyn,

actually i wanna to thank u for ur efforts to help me.

first i think the problem is that i donot understand
BackgroundWorker well (it is very complicated)

so i tried before using it to use normal thread but i failed
but now i knew my error and i fix it in the normal thread not the BackgroundWorker Thread and now no(unreachable code,memory leak ...)these things are not found now

any way thanx to u very much
bye

Generator

Luc Pattyn8-Apr-07 13:05

How to specify an event handler

8-Apr-07 13:05

You're welcome.

Luc Pattyn

[My Articles]

Get Controls by name

swjam4-Apr-07 5:03

swjam

4-Apr-07 5:03

Is there a way to access each of the controls in a form by name programmatically?
i.e. without having to loop through each one
Tia.

I am a SysAdmin, I battle my own daemons.

Re: Get Controls by name

B.King4-Apr-07 5:50

B.King

4-Apr-07 5:50

Yes,
use the Controls Property of a Contailer like Form or Panel:

<br />
Control c = Controls.Find("name", true);   // if this is a Form<br />
Control c = panelXYZ.Controls.Find("name", true);   // if panelXYZ is a Panel ...<br />

peterchen4-Apr-07 5:02

peterchen

4-Apr-07 5:02

If I have a class with an event, and a class that wants to attach to the handler:

class A
{
  public event EventHandler<SomeEventArgs> SomeEvent;
}

class B
{
  public void AttachToHandler(A a)
  {
    a.SomeEvent += ***;  // << here's my question
  }
   
  void SomeEventHandler(object sender, SomeEventArgs e) {... }
 
}

The VC# Express IDE ("press TAB to insert..") suggests:

a.SomeEvent += new EventHandler<SomeEventArgs>(SomeEventHandler);

However, the following also seems to work:

a.SomeEvent += SomeEventHandler;

Now the questions:
Is there a difference between the two? A "preferred style"?

We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
My first real C# project | Linkify!|FoldWithUs! | sighist

Re: How to specify an event handler

mikanu4-Apr-07 6:48

mikanu

4-Apr-07 6:48

I've always used the first method (using the New operator to instantiate a new delegate that will handle the event).
You can alway declare a variable that holds the reference to the event handler in advance and then use that as your handler like so:

<br />
<pre>   
   EventHandler eh;
   eh = New EventHandler(SomeEventHandler);
   a.SomeEvent += eh;
</pre><br />
<br />
this way you could later detach the event handler too, like so:<br />
<br />
<code lang="C#"><br />
<pre>
   a.SomeEvent -= eh; //(as long as eh still references your event handler!)
</pre><br />
<br />
The second way seems to be a shortcut for the first (in which the compiler automatically generates the code that instantiated the delegate and than passes it your function).<br />
<br />
Hope this helps, but your best bet is to do some reading on delegates and event handlers in C#. <br />
<br />
 <br />
<br />
<div class="ForumSig">----<br />
<a href="www.digitalGetto.com">www.digitalGetto.com</a></div>

Multi-select ComboBox

Amatista4-Apr-07 4:46

Amatista

4-Apr-07 4:46

Hi,

I would like to have a ComboBox with multi-select, which is similar to ListBox (but ListBox has no DropDown). Could someone here give me some help? Thanks in advance.

BTW, I use Microsoft Visual Studio .Net 2005.

Regards,
Amatista

Douglas Troy4-Apr-07 6:00

Douglas Troy

4-Apr-07 6:00

Why would you want to do this? A ComboBox can only show a single selection at a time, when the list is not dropped, so therefore, a MultiSelect ComboBox makes no sense; which is why it's not an option ...

:..::. Douglas H. Troy ::..

Bad Astronomy |VCF|wxWidgets|WTL

Amatista4-Apr-07 22:27

Amatista

4-Apr-07 22:27

Thanks for your reply.

I am in charge of designing a full-text searching tool, a windows application, and the ComboBox is used for user to select file types for searching. I think it would be better if the user can select more than one file types. For the selected file types, if more than one item, they should be displayed, either comma or semicolon separated. Or is there another tool instead of ComboBox that I can use?

Does anyone have any suggestions to solve this issue?

Douglas Troy5-Apr-07 5:34

Douglas Troy

5-Apr-07 5:34

You should either be using a group of check box controls or a CheckedListBox. What you're wanting to do, goes against the standard design for that control.

:..::. Douglas H. Troy ::..

Bad Astronomy |VCF|wxWidgets|WTL