Explicitly call IDispose() method - C# Discussion Boards

8-Jul-09 9:41

Hello all,

Does anyone know if the Dispose() method must be explicity called on every object that implements IDispose? In other words, will the Garbage collector call the Dispose() method when the object's life expires. Don't get me wrong, I know that it's good practice to clean up your own trash but I didn't know how serious of a memory leak this issue is.

In addition to that, what about un-wiring event handlers from a class before it's reference is set to null? I've code that removes handlers and code that doesn't.

Any thoughts?

The hurrier I go, the behinder I get.

Luc Pattyn8-Jul-09 10:46

Luc Pattyn

8-Jul-09 10:46

Hi,

this is how I understand it:

1. you should call Dispose(), it makes life easier for the GC, and it frees resources sooner.

2. Managed objects that die will be disposed by GC if and when it runs; it does not run when no more memory requests are needing a garbage collection, and in particular when an app terminates.

3. you must make sure Dispose() is called when unmanaged objects are involved.

4. you don't know (unless it is documented) whether managed classes create unmanaged objects internally, so call Dispose!

5. A process exiting will clean up everything, which does not imply your resources will be in a state you like; e.g. a process will close its open files, it may not have written the closing texts to it if you don't take care.

6. When you hand over a delegate, it includes a "this" pointing to the object on which the delegate is to be called. So passing a delegate to a live object keeps your object alive too. But not the other way around, so it is no problem most of the times.
Example1: your class instantiates a dialog and passes a delegate to one of the dialog buttons; the dialog keeps your class alive, but it was modal anyway. When the dialog closes, it gets disposed and the delegates are gone.
Example2: your form passes a delegate to an object (maybe a singleton) that lives for the life of your app, e.g. to get signaled when a logging component gets a problem, say a disk full condition. When you close your form, it remains alive because of the delegate. If all your forms do this, none of them ever releases its memory.

Smile | :)

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Richard Blythe8-Jul-09 11:08

8-Jul-09 11:08

Thanks Luc!

I agree that just because some class is managed, doesn't mean that it will not call unmanaged code. (Good point)

You've definitely cleared up some question marks in my brain!

The hurrier I go, the behinder I get.

N a v a n e e t h8-Jul-09 17:25

N a v a n e e t h

8-Jul-09 17:25

Richard Blythe wrote:
what about un-wiring event handlers from a class before it's reference is set to null? I've code that removes handlers and code that doesn't.

AFAIK, you don't have to unwire each event. Setting it to null will remove the invocation list.

Navaneeth

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Luc Pattyn8-Jul-09 22:50

Luc Pattyn

8-Jul-09 22:50

However, if consumer1 and consumer2 both wire to some event in producer3, and only consumer1 wants to exit the game, then noone is allowed to set the event to null since that would break the producer3-consumer2 relation.

Smile | :)

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N a v a n e e t h9-Jul-09 16:40

N a v a n e e t h

9-Jul-09 16:40

Yeah. That's right Smile | :)

Navaneeth

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Curtis Schlak.8-Jul-09 17:39

Curtis Schlak.

8-Jul-09 17:39

As far as I'm concerned, the definitive article on finalizers and disposable objects can be found over on Joe Duffy's Blog[^].

"we must lose precision to make significant statements about complex systems."
-deKorvin on uncertainty

Custom Treeview with Overridden OnPaint & WndProc

Daniel Grunwald9-Jul-09 3:38

Daniel Grunwald

9-Jul-09 3:38

I absolutely disagree with the "Dispose(bool)" pattern.
It's verbose and hard to use correctly. And it's only really useful when a class contains both managed and unmanaged resources, and there might even be derived classes that have their own unmanaged resources.
The solution is simple: don't do that.

Instead, create a sealed class for each unmanaged resource (bonus points if its derived from SafeHandle). Then your other classes only have to deal with managed resources, so they never need a finalizer and the Dispose method is trivial (just call Dispose on all members).

For more details, take a look at Stephen Cleary's article 'IDisposable: What Your Mother Never Told You About Resource Deallocation'[^].

VengefulSakhmet8-Jul-09 9:38

VengefulSakhmet

8-Jul-09 9:38

I am attempting to do a custom OnPaint on a custom Treeview with a lot of bumps along the way. At this point in the game, I'm just trying to get a purple rectangle to print out anywhere involving this TreeView. I'll work on the bounds afterwards.

I found out the long way that WndProc turns off OnPaint and am trying to now to override WndProc, but I have absolutely no idea what to pass to OnPaint seeing this is my first attempt at GDI and from all the examples I've been looking at OnPaint appears to be called implicitly by other Win Forms. Please point me in the right direction.

public class myProfileTree : System.Windows.Forms.TreeView
{
protected override void OnPaint(PaintEventArgs e)
{
Graphics g = e.Graphics;
SolidBrush brush = new SolidBrush(Color.MediumOrchid);
Rectangle blueRectangle = new Rectangle(50, 50, 200, 100);
g.FillRectangle(brush, blueRectangle);
}

protected override void WndProc(ref Message m)
{
switch (m.Msg)
{
case(15):
{
OnPaint( Confused | :confused:

);
break;
}
default:
{
break;
}
}
base.WndProc(ref m);
}
}

Re: Custom Treeview with Overridden OnPaint & WndProc

Richard Blythe8-Jul-09 9:44

Re: Custom Treeview with Overridden OnPaint & WndProc

8-Jul-09 9:44

As obvious as it seems, have you set the DrawMode to: TreeViewDrawMode.OwnerDrawAll?

The hurrier I go, the behinder I get.

VengefulSakhmet8-Jul-09 10:55

VengefulSakhmet

8-Jul-09 10:55

Not entirely sure that is the direction I want to be taking. This just appears to erase my entire custom treeview with no call to OnPaint.

I'm trying to keep the way the rest of the nodes aside from a selected node to look the norm. I need to keep the selected node the focus color as buttons are pressed even though this goes against standard convention. The thought was to make a custom treeview with custom onpaint to repaint this one node with a rectangle using onpaint and then putting back the original text on top.

Then I read this: http://www.codeproject.com/Messages/685886/Re-Custom-Tree-View-Painting.aspx and came to the overriding WndProc, but was unsure on how to procede with the call to OnPaint.

Re: Custom Treeview with Overridden OnPaint & WndProc

Richard Blythe8-Jul-09 11:14

Re: Custom Treeview with Overridden OnPaint & WndProc

8-Jul-09 11:14

I need to keep the selected node the focus color

If that's all your after then set the: "HideSelection" property to false. This setting allows you to retain visibility of the selected node once the treeview has lost focus.

If you still want your own paint, just manualy set the node's properties:

tv.SelectedNode.BackColor = SystemColors.Highlight;
...

The hurrier I go, the behinder I get.

VengefulSakhmet8-Jul-09 11:57

VengefulSakhmet

8-Jul-09 11:57

HideSelection will not work for this instance and changing the BackColor will not address the issue I have. My button moves the selected node up and down. Since it is no longer the focus, it turns from medium blue to light gray. I did however figure out how to override WndProc:

protected override void WndProc(ref Message m)
{
base.WndProc(ref m);

switch (m.Msg)
{
case (15):
{
PaintEventArgs pae = new PaintEventArgs(
Graphics.FromHwnd((m.HWnd)),
new Rectangle(0, 0, this.Width, this.Height));

OnPaint(pae);
break;
}
default:
{
break;
}
}
}

Thanks for trying!

Copy Excel Rows using C#

kasi148-Jul-09 9:01

kasi14

8-Jul-09 9:01

Hi All,

I am working on a c# tool to copy part of excel rows to another excel sheet.

i.e i want to copy row 5 to row 10 in Excel1 and create a new exce2.

any sample code will be helpfull.

Regards,
Kasi

Manas Bhardwaj8-Jul-09 9:35

Manas Bhardwaj

8-Jul-09 9:35

Well, there are a couple of options.
You can use Office Interops to read the excel file and then create the second with the data of your interest.
Another way can be to read the excel sheet using the ADO connection into a dataset and you can write the selected rows as a xml file (using Dataset.writeTo method). Excel can easily read the xml file. Rose | [Rose]

Manas Bhardwaj
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kasi148-Jul-09 10:52

kasi14

8-Jul-09 10:52

Hi,

Thanks for your quick reply. Can you send me some sample code.

Regards,
Kasi

EliottA8-Jul-09 11:04

EliottA

8-Jul-09 11:04

What have you tried already? Have you researched how to do read and write from excel files? Many people don't like doing work for free, and 'sample' code exists on the internet everywhere, if you have tried using google that is.

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