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Hello,
I'm relatively new to C# and used C++ before. Perhaps you have a solution to my problem, I couldn't find one in several books:
When I write a class in C++ like
<br />
class MyClass<br />
{<br />
CFirst m_First;<br />
CSecond m_Second;<br />
<br />
MyClass()<br />
{<br />
}<br />
<br />
~MyClass()<br />
{<br />
m_First.DoSomething();<br />
}<br />
<br />
}<br />
This is what happens in C++ when MyClass gets instanciated:
m_First gets instanciated
m_Second gets instanciated
MyClass constructor is called
when the MyClass object gets destroyed:
MyClass destructor gets called
m_Second gets destroyed
m_First gets destroyed.
The problem in one of my C# classes is:
I wrote myself a small logger class with an internal buffer. The data only gets written to disk when the buffer is full. I use a streamwriter for this. When my destructor gets called, I want to check if theres any data left in the buffer ans write it to disk, so the user of my class doesn't have to use a close() method when he doesn't use my logger anymore. But when I try to write to the streamwriter in my destructor, I get an E/A exception. I figured out, that my streamwriter seems to be destroyed before my destructor gets called. How can I circumvent this? The IDisposable interface doesn't solve my problem because:
a) you cannot use it when you use my class as a member variable
b) it is not guaranteed that the user of my class uses it
This is the same problem as the streamwriter has. A small program like
StreamWriter sw = new StreamWriter(@"c:\hello.txt");
sw.WriteLine("Hello World");
will leave you with an empty hello.txt file when you forget to do an explicit sw.Close().
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Unfortunately, there's no way around this in C#, except using IDisposable. Because .NET is a garbage collected environment, there is no way to guarantee finalization of one object before/after another. And that's why StreamWriter works the way you described.
Stylez Daviz wrote: The IDisposable interface doesn't solve my problem because:
a) you cannot use it when you use my class as a member variable
I don't understand the reason for a). Class member variables can be types that implement IDisposable.
Stylez Daviz wrote: b) it is not guaranteed that the user of my class uses it
You're right, but that's how most classes in the BCL work. The "using" statement can help things a bit, but not much.
In case you are interested, C++/CLI (the new MC++) has deterministic destruction (simulated by the compiler, of course).
Regards
Senthil
_____________________________
My Blog | My Articles | WinMacro
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S. Senthil Kumar wrote: I don't understand the reason for a). Class member variables can be types that implement IDisposable.
They may implement IDisposable, but how do I use it then?
I can't use using(MyClass x = new MyClass()) outside of a class' method right? And I cannot invoke x.Dispose() from my destructor because than its already too late and my member variable could have been cleaned out by the GC.
If there's no way to get around of this problem I#ll have to accept it but I don't know why it's implemented this way. It transfers resposibility to the user of the class (like calling close() or Dispose()) where in C++ for example the user could rely on the class to handle this situation. Why can't my member variables be marked as "used" so they will only be collected by the GC when my destructor has finished? I don't know how JAVA does it, maybe I'll check it out.
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Hi!. I'm very new in C#. still i'm learning C#.
1) Will C# allow us to do some graphs such as tan, sin?
2) Will it support integration, differentiation and some more functions?
if so can i have some sample code pls
RAMA
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myrama wrote: Will C# allow us to do some graphs such as tan, sin?
Yes
myrama wrote: Will it support integration, differentiation and some more functions?
Yes
myrama wrote: if so can i have some sample code pls
The Graphics class contains the method to draw your points. If you type Math., the intellisense will show you all the Math functions, such as Math.Sin, Math.Cos, Math.Abs, etc.
Christian Graus - Microsoft MVP - C++
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 my english is so poor ....
so pardon me... XD
i got a problem since i used Nhibernate to access data.
it is in effect that xml-serialize a entity-object,
but there are something wrong when i xml-serialize the IList object by NHibernate o/r mapping framework
help me to through the dammit problem ... 3q 谢谢！
if there is anything you need,it won't be far. <<forest gump="">>
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Hi-
I've created an ImageList, and a Toolbar. I've 'hooked up' each toolbar button to its corresponding Image from the image list. The images are visible in design time, HOWEVER, when I build and run the application, the Toolbar Button images are NOT visible! The buttons are there, but they are blank!
Does anyone have any idea what the problem is? I've tried an imagelist of *.ico's and also an image list of *.gif's.
Any help would be greatly appreciated!
Thanks
Warwick
"I hear they've even got the internet on Computers now." - Homer Simpson
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For i = 0 To Controls.Count - 1<br />
Select Case TypeName(Controls(i))<br />
Case "TextBox"<br />
Controls(i).Text = ""<br />
Case "Label"<br />
Controls(i).Caption = ""<br />
End Select<br />
Next i
Kindly Please convert it to c# syntax
~Thanks
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for (int i = 0; i <= Controls.Count - 1; i++) \
{
if (TypeName(Controls(i)) == "TextBox")
{
Controls(i).Text = "";
}
else if (TypeName(Controls(i)) == "Label")
{
Controls(i).Caption = "";
}
}
Get Sharpdevelop. It is a free development environment, and it has a VB.net to C# converter.
Edit: You can get SharpDevelop at http://www.icsharpcode.net/
Pumk1nh3ad illustrates that Intelligent Design oft goes awry. - Ed Gadziemski
-- modified at 2:54 Sunday 13th November, 2005
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Thanks for the immediate reply but I still have the same error, we have the same syntax conversion.
The name 'TypeName' does not exist in the class or namespace 'Maintenance.Administration'
~dabuskol
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The automatic C# converter did not convert the TypeName function. It is exclusive to vb. try this.
for (int i = 0; i <= Controls.Count - 1; i++)
{
if (Controls[i].GetType().Name == "TextBox")
{
Controls[i].Text = "";
}
else if (Controls[i].GetType().Name == "Label")
{
Controls[i].Caption = "";
}
}
Pumk1nh3ad illustrates that Intelligent Design oft goes awry. - Ed Gadziemski
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Try this. It's not exactly the same code, but is more efficient and give the same results.
foreach (Control nextControl in this.Controls)<br />
{<br />
if (nextControl != null)<br />
{<br />
if (nextControl is Label)<br />
((Label)nextControl).Text = String.Empty;<br />
else if (nextControl is TextBox)<br />
((TextBox)nextControl).Text = String.Empty;<br />
}<br />
}
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hello...
I am using the htmleditorcontrol provided by microsoft consulting services..
i want be able to add videos and audios to the output:the html document.
i know a i have to change the
"HtmlControl.SelectedText" but i don't know the exact code and do i have to use any plugins.
can anyone please help me on this
your help will be appreciated
thanx
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how can i close child form?
debugger gives this error : An unhandled exception of type 'System.NullReferenceException' occurred in market.exe
Additional information: Object reference not set to an instance of an object.
and i use it this line for closing: this.ActiveMdiChild.Close();
pleae help me
Thanks
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And what does the call stack show? Where is this null reference occurring? What is null that wasn't expected to be null?
You need to find that point, then set a break point in the debugger just before that happens to see why you are getting a null.
My: Blog | Photos
"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucious
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lets say the form name which has MdiChild u want to close is market:
market.ActiveForm.ActiveMdiChild.Close();
i`m not sure if it works maybe u can give more detailts about the code
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thanks for your help but i thought wrong simply it closes like a other form e.g. this.close(); or just close();
thanks again
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I have an automation program in C# (latest version with .Net 2.0) that takes control of an instance of IE 6.0 using ShDocVw.dll reference. The other reference is the .NET Microsoft.mshtml.dll. When you navigate to a page with frames, only the top frame is available to use as a document object. I want to programmatically click on a link that is in a frame. I have tried everything to get a reference to the frame and I am getting casting errors in VS. For instance:
InternetExplorer ie = new InternetExplorerClass();
ie.Visible = true;
string url = "http://www.iopus.com/iim/demo/v4/frames/";
Object o = null;
ie.Navigate(url, ref o, ref o, ref o, ref o);
//put a stop here to give time to load all the frames
mshtml.HTMLDocument doc = (mshtml.HTMLDocument)ie.Document;
IHTMLElementCollection fcollection = (IHTMLElementCollection)doc.getElementsByTagName("FRAME");
IEnumerator fEnum = fcollection.GetEnumerator();
fEnum.Reset();
fEnum.MoveNext();
foreach (HTMLFrameElement fElement in fcollection)
{
Console.WriteLine(fElement.tagName + fElement.name);
if (fElement.name == "bottom")
{
object frmNo = 8;
// here it is...
mshtml.IHTMLWindow2 frame = (mshtml.IHTMLWindow2)doc.frames.item(ref frmNo);
}
}
The cast for IHTMLWindow2 does not work. I have tried casting to other things like HTMLDocument, etc and nothing will cast.
The only thing I have found so far that works is to take the src url of the frame and navigate directly to it, then I have the document object available to work with. This method seems wrong. I should be able to enumerate the frames collection and then work with each frame individually.
Has anyone had any luck doing this correctly?
David Bicknell
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Hello,
I am having a problem with set AllowDrop from a callback function for
any types of control boxes, ie. ListView. The following is the example
code that creates the problem. The listView1.AllowDrop never get set
and there is no error or warning as well. Also, if there is any code
after the line "listView1.AllowDrop = false;" will never get excuted.
It seems only happen to the AllowDrop property, others, such as color,
Enabled, are fine.
There is no problem to set AllowDrop from the main thread. For example,
it can be set successfully from the button2 (see below).
I am using .NET 1.1 on Windows XP(SP2).
I appreciate if anybody can help me out here.
Thanks.
John
-------------------------------------------------------------------------------------------
public delegate void ipcEventCallback();
public static ipcEventCallback ipcEventHandler;
private void Form1_Load(object sender, System.EventArgs e)
{
// Init ipcEventCallback interface
ipcEventHandler = new ipcEventCallback(IpcEventHandler);
}
void IpcEventHandler()
{
listView1.AllowDrop = false;
}
private void button1_Click(object sender, System.EventArgs e)
{
ipcEventHandler.BeginInvoke(null, null);
}
private void button2_Click(object sender, System.EventArgs e)
{
listView1.AllowDrop = false;
}
-------------------------------------------------------------------------------------------
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button1_Click(object sender, System.EventArgs e)
{
ipcEventHandler.BeginInvoke(null, null);
}
This invokes the delegate on a different thread. When the delegate is invoked and it attempts to change the ListView's AllowDrop property, it is doing so from a different thread than the one the ListView is running on. That's a no-no. You're only suppose to modify controls on the thread in which they are running.
Is there a reason to use a callback here? Why not do it the way you have in the button2_Click event handler?
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Thanks for reply.
I understand it's from another thread, but only this AllowDrop cannot be modified. Other properties can be changed without any problem. Do you know why is that? I think it may be a problem for .NET.
My application is a process with two threads, GUI and a background running thread. The backgroud thread running as a client communicates with a server and sometimes it needs to update the GUI. The GUI provides a set of callback interface for background thread to use to update the GUI. One of the callback function wants to change a controller's AllowDrop field. From the articles I read, it's the right way to modify GUI through callback thread... I cannot think any other better way since I don't want to block the GUI in anyway.
Thanks,
John
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xjsun wrote: I understand it's from another thread, but only this AllowDrop cannot be modified. Other properties can be changed without any problem. Do you know why is that?
Not a clue. That is strange. Which version of Visual Studio are you using?
xjsun wrote: From the articles I read, it's the right way to modify GUI through callback thread...
Hmm, interesting! I would have thought that since the callback is running on a different thread, via the delegate's BeginInvoke method, that it would be prohibited from modifying the GUI, but there must be some things here I'm not aware of.
xjsun wrote: I cannot think any other better way since I don't want to block the GUI in anyway.
I can understand that. And it rules out suggestiong that you use the Form's BeginInvoke method because it would marshal the delegate invocation to the GUI's thread.
Sorry I can't be of more help.
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xjsun wrote: From the articles I read, it's the right way to modify GUI through callback thread
No, this[^] clearly says that
There are four methods on a control that are safe to call from any thread: Invoke, BeginInvoke, EndInvoke, and CreateGraphics. For all other method calls, you should use one of the invoke methods to marshal the call to the control's thread.
I have a strong suspicion that that is what is causing the problem.
Regards
Senthil
_____________________________
My Blog | My Articles | WinMacro
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