Removing an EventHandler??? - C# Discussion Boards

4-Feb-04 10:34

HTTP is a stateless protocol, allowing only one-way communications (clients make a request, server returns a response). You couldn't use a callback because the server can't alert the client. You could, however, use a session variable to signify when a particular action is done so that when the client receives the response from the server after this variable is set, you can display something to link them to the generated Excel file. You don't even need XML Web Services to implement such a feature. This isn't an easy task, though, and you should better familiarize yourself with how ASP.NET works by reading the .NET Framework SDK, specifically the topics related to ASP.NET[^].

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IntPtr and Strings

Tristan Rhodes4-Feb-04 10:10

Tristan Rhodes

4-Feb-04 10:10

I'd like to experiment with an IntPtr and strings. How do i retrieve a string from an IntPtr and convert a string to an IntPtr for the purpose of marshaling?

Basicaly, I've built a version of SHGetPathFromIDList in my program and i'm converting a PIDL to the file path, however the pre created string I am marshaling to it does not get modified properly, so i would like to send a pointer to a string instead.

(There is a post about this problem in the COM forum that covers the finer details, but for now i'd just like to convert an IntPtr to a string or Vis Versa.)

Cheers

Cata

Edit: I suppose the question is - How do I construct a buffer (char array?) of size Max_Path, and then create a pointer to it?

Heath Stewart4-Feb-04 10:29

4-Feb-04 10:29

See the System.Runtime.InteropServices.Marshal class. It has a lot of static methods to facilitate marshaling between things like Strings and IntPtrs. For a specific method, see Marshal.PtrToStringAuto (methods exist for ANSI, BSTR, and Unicode as well when you know that a string will always be encoded a certain way, otherwise Auto is ANSI on Windows and Unicode on Windows NT.

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Tristan Rhodes4-Feb-04 10:38

Tristan Rhodes

4-Feb-04 10:38

Thanks heath.

Just tell me, am I on the right track for handling a buffer? I take it I am constructing a space in memory that will have the file path written to it.

It's not an out, or ref call is it? I just need to retain the pointer to the buffer so that once it has been written, I can read it.

How do I go about this? Using a pointer to a string?

Cheers

Cata

Edit: Thanks dude! I got it figured, switched the string into a pointer, and forwarded the pointer, pulled it out, converted it back... and bingo! Smile | :)

Gratz. My experimentation with COM goes very well indeed Smile | :)

Heath Stewart4-Feb-04 10:44

4-Feb-04 10:44

Did you ever read all that stuff on marshaling I gave you links for before? ref and out should only be used for [out] value types and pointers to pointers as declared in native code. If you need the address to a string, you simply do something like this:

IntPtr ptr = Marshal.StringToCoTaskMemAuto(myString);

If your method declaration expects a pointer, this is how you can get it. If you're passing a char[] array, the array itself is a reference type (even though Char is a value type) so you don't need ref or out. The address is what's already being passed since the array is a reference type.

It all just depends on the implementation, for which you've given no specifics. If you need help with something specifically, please provide the signature of the method you're trying to call or something similar.

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Removing an EventHandler???

Tristan Rhodes4-Feb-04 10:46

Tristan Rhodes

4-Feb-04 10:46

Yeah, sorted it all.

Thanks mate, probably posted too soon. Got it figured.

Gratz.

Cata

LongRange.Shooter4-Feb-04 9:21

LongRange.Shooter

4-Feb-04 9:21

I have one form that is subscribing as an EventHandler to an event on the parent form.

It is possible for the user to close this form but still have the parent open.

Is there a way that I can remove myself as a delegate to that event? You know...like a "parent.EventType -= this.EventHandler;"

_____________________________________________
_{Of all the senses I could possibly lose,
It is most often the one called 'common' that gets lost.}

Re: Removing an EventHandler???

Heath Stewart4-Feb-04 10:27

Re: Removing an EventHandler???

4-Feb-04 10:27

Yeah, same way you add it - you were close:

parent.Event -= new EventHandler(this.handler_Method);

You don't even need to hold a reference because a delegate is a managed function pointer and the function (actually, method) doesn't move.

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LongRange.Shooter5-Feb-04 2:22

LongRange.Shooter

5-Feb-04 2:22

Thanks Heath.

I thought about doing that....but it seems a bit counter-intuitive that you tell the parent to remove a new EventHandler.

Later,

Michael

_____________________________________________
_{Of all the senses I could possibly lose,
It is most often the one called 'common' that gets lost.}

Re: Removing an EventHandler???

Heath Stewart5-Feb-04 4:18

FileInfo.ValidateFIleName

5-Feb-04 4:18

It is only a new delegate but the delegate references the same method (of the same instance), so it will get removed. You can keep a reference to your delegate you added initially if you don't believe me, but trust that it works this way.

As far as who removes event handler is up to your design. If the child form is hooking into its parent form, then the child should remove the event handler for a better OO design. You could do this in the Closing or Closed event if you like, but know that the event handler will be nullified and garbaged collected if the child reference gets destroyed. It really isn't necessary in such a case.

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elena123454-Feb-04 8:07

elena12345

4-Feb-04 8:07

Is there a way to validate a file name in C#?

I know I could easily code this up myself, but this is something everyone always needs, so I am in total denial that there is no function like that in C# libraries. OMG | :OMG:

Thanks,

Elena

Re: FileInfo.ValidateFIleName

Not Active4-Feb-04 8:38

Not Active

4-Feb-04 8:38

What do you mean validate a file name? Validate how? That it matches some naming scheme, is a certain length? Then the answer is no.

Re: FileInfo.ValidateFIleName

John Kuhn4-Feb-04 8:48

John Kuhn

4-Feb-04 8:48

Try creating a file using an invalid file name and see if an exception happens, and handle the exception.

XML Web Services question

Chen Venkataraman4-Feb-04 7:23

Chen Venkataraman

4-Feb-04 7:23

After playing with XML Web Services a little bit, it looks like all the data members of any custom object that need to be serialized across should be marked as public. This seems so non O-Oish or is this a limitation of the WSDL that gets generated automatically that it only supports public data members.

For e.g.

  [Serializable]<br />
	public class SomeData <br />
	{<br />
		public string	_id;   // if this is marked private, WSDL ignores it<br />
<br />
		public string Id <br />
		{<br />
			get { return _id; }<br />
		}<br />
	}<br />

Is there a way around this?

Chen Venkataraman

Re: XML Web Services question

Andy Brummer4-Feb-04 8:56

Andy Brummer

4-Feb-04 8:56

It's due to the way xml serialization works. It doesn't actually remote the object like you would think. What happens is that wsdl.exe creates a class on the client that is serialziation comatible with your class, with none of the methods. It will just be a simple struct with data fields only.

Re: XML Web Services question

Heath Stewart4-Feb-04 8:59

Re: XML Web Services question

4-Feb-04 8:59

Only the property needs to be public. Your field that stores the actual value should be marked private. You want WSDL to ignore it and only pay attention to the public property. After all, why include values for both _id and Id, which actually are the same object?

If you want more control over the WSDL that's generated, see the attributes in the System.Xml.Serialization namespace, as well as those in the System.Web.Services and System.Web.Services.Protocols namespaces.

There is plenty of documentation about these in the .NET Framework SDK.

Besides, remember that the Web Service is just another class that code can call via a proxy. Classes can only access public members of other classes unless they're derived from that class. This is how code access is supposed to work.

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Michael Potter4-Feb-04 9:15

Michael Potter

4-Feb-04 9:15

XML Serialization only serializes public data.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpovrSerializingObjects.asp

Chen Venkataraman wrote:
Is there a way around this? Yes
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemRuntimeSerializationISerializableClassTopic.asp

Or you can do a binary serialization to a MemoryStream and send it as a byte array. I have used this method successfully with an intermediate compression/encryption pass.

Tab control question

Shizam4-Feb-04 5:47

Shizam

4-Feb-04 5:47

What I'm trying to do is have a tree view on the left of my SDI view, and depending on what's selected in that, display a different "form" or view on the right hand side. I'll want to have a dynamic amount of views, depending on how many items are in the tree view. All the data in the different views will be updated constantly, but only the selected one will display.

Any ideas how to accomplish this?

The Tab Control looks promising, but I'm wondering if there's another way, and I don't want the actual tab, because selection will be done via the tree control.

Thanks,

Peter

Heath Stewart4-Feb-04 6:04

4-Feb-04 6:04

All you need to do is associate a Type with your TreeNode and create an instance of that when needed. You could also instantiate an instance with each TreeNode, but that would make memory consumption very high (depending on how many TreeNodes you have).

For example, derive from TreeNode with your own class and add a ControlType property (or whatever you want to call it) of type Type. In the handler for the TreeView.AfterSelect method, you can do something like this:

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
  Type t = ((MyTreeNode)e.Node).ControlType;
  Control c = (Control)Activator.CreateInstance(t);
  containerControl.Controls.RemoveAt(0); // Assumes single control
  containerControl.Controls.Add(c);
}

The containerControl represents the Panel or whatever hosts the control to be created in your form on the right side. Please note that this is a very simplistic example but should give you some idea.

There's also a few articles here on CodeProject that use a similar approach for tree-driven preference dialogs/controls. For one example, see A Designable PropertyTree for VS.NET[^].

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Shizam4-Feb-04 8:00

Shizam

4-Feb-04 8:00

Thanks, that's exactly what I needed.

Peter

Alex Korchemniy4-Feb-04 8:02

Alex Korchemniy

4-Feb-04 8:02

But is there a way of preventing the tab from drawing?

(I have a similar problem that has to do with the CrystalReportViewer. I'm trying to customize the control more than it allows. It would be great if I can just take the control and parent it to a panel, but part of the implementation is in the tabcontrol so that didn't work out.)

Heath Stewart4-Feb-04 8:44