C# Discussion Boards - CodeProject

12-Jun-07 6:28

I have the situation where Form A is hidden when Form C is displayed and then when Form C is closed, Form A is displayed again. Almost all of the time it works as expected. Occasionally, though, both forms are seen displayed at the same time. For the most part, no one can tell me the steps they went through when it happens. It has been witnessed mostly in debug mode. The one time it happened in release mode was also the one time we knew the steps that led it to happen - a test procedure was being run. However, when the test procedure was repeated at a later date the 2 windows were correctly mutually exclusive. Any ideas?

Description of the code:
When ClassB is instantiated, it sets the member variable m_FormCOpen = false. Later, upon user selection, FormA will call method1 in ClassB. method1 instantiates FormC, subscribes to the closed event for FormC, sets m_FormCOpen = true, displays FormC, does some database updating, and returns. The method in FormA checks the property for m_FormCOpen and if it is true, hides FormA. The method in ClassB that is executed when FormC closes, triggers an event to which FormA has subscribed, and FormA is displayed.

public class FormA
{
   public FormA (ClassB)
  {
     m_ClassB = ClassB;
  }

  private void ClassA_Load ()
  {
    subscribe to ClassB ClosedFormC – routine to call: ClassB_ClosedFormC.
  }

  private void UserSelection_Click()
  {
     m_ClassB.method1();
     If FormCIsOpen 
    {
      Hide();
     }
  }

   ClassB_ClosedFormC()
   {
     Show();
   }
} // end of ClassA


public class ClassB
{
  public void ClassB()
  {
    m_FormCOpen = false;
  }

  public void method1()
  {
    FormC m_FormC = new FormC();
    subscribe to FormC.Closed – method to call FormC_Closed
    m_FormCOpen = true;
    m_FormC.Show();
    do some stuff
  }

  private void FormC_Closed
  {
     trigger ClosedFormC
     m_FormCOpen = false; 
  }

  bool FormCIsOpen
  {
    get
    {
      return m_FormCOpen;
    }
  }
}// end ClassB

Luc Pattyn12-Jun-07 6:48

12-Jun-07 6:48

Hi,

I am not surprised it behaves strangely:
the "code" shown is a complete mess; it is not valid C# code, and it is convoluted.

Why have variables m_FormC, m_FormCOpen and FormCIsOpen all side-by-side ?
It would be much better to have just one m_FormC somewhere, and one method to determine
whether this m_FormC is open or not, rather than having several bools that try to keep
track...

Smile | :)

Luc Pattyn

[My Articles] [Forum Guidelines]

theFrenchHornet12-Jun-07 8:05

12-Jun-07 8:05

I realize it is not valid C# code - I said it was a "Description" of the code. I did not put it in red as the code tag would do, and I mentioned that it works most of the time. If this were truly the 'code', it would not be compiling far less working most of the time. The true code has been executed by 11 people, 6 hours a day, for 2 years. In that time the error situation I am describing has occurred about 4 times. The code itself sits on another computer and is too voluminous to reproduce here. This is not a syntax problem. If someone is on the level where they could answer this question, I think they are at the level they can fill in the blanks in the outline and perfect C# is not needed.

I don't know what you mean by side-by-side and what that has to do with how code executes. The 3 items you mention serve different purposes. m_FormC is the class itself. m_FormCOpen is the boolean that tracks whether the form is dipslayed or not. Remember, the class can be instantiated but the form not necessarily displayed at a given time. FormCIsOpen is the property which allows other classes access to the member variable m_FormCOpen. Thus, you see, there are not several bools that try to keep track - there is only one. There are reasons why one class displays the form and another needs to know if it is displayed or not. The question is, that being the case, is there a safer way to accomplish it. Or, is there a known Windows/.NET problem where forms in hiding suddenly come out of hiding. You haven't given a meaningful alternative or any explanation for why the methodology here would fail.

My impression is you were too quick to respond. Slow down. If you don't want to take the time to understand something that isn't immediately obvious to you, it would be better to not respond at all than to do so in a nonconstructive manner. Saying the code is a complete mess is not constructive. Confusing a class with a bool with a property is not constructive. But, if you were truly trying to be helpful, then thanks for taking the time. Wink | ;)

Luc Pattyn12-Jun-07 8:33

12-Jun-07 8:33

A form knows whether it is visible or not, there is no need to try to keep that in a boolean.

Less code = less bugs
Better readability = better code

Smile | :)

Luc Pattyn

[My Articles] [Forum Guidelines]

theFrenchHornet14-Jun-07 3:43

14-Jun-07 3:43

For this design, there is. Note that 'the boolean' is in ClassB - not FormC. FormC does know when it closes, but method1 has already finished its execution by this time. FormC alerts others to its closing via an event. ClassB sets the boolean based on this event. ClassA can now access the information via a property provided by ClassB. ClassB has visibility to FormC. FormA does not. Thus, FormA cannot ask FormC are you open or closed.

Shy Agam12-Jun-07 9:11

Shy Agam

12-Jun-07 9:11

Well... I realize that this is not the real code, but rather a pseudo code of it...
However, it looks like this code is not thread-safe.
This means that there might be a chance that sometimes, under certain circumstances, m_FormCOpen is misleading your program because of thread-safety issues.

If you don't know what "thread-safe" means, I'de suggest reading on the following topics:
- Thread Safety
- Threads Synchronization
- Locking Mechanisms.

Smile | :)

Good luck,
Shy.

Guffa12-Jun-07 9:13

Guffa

12-Jun-07 9:13

Here's a theory:

If someone clicks twice in FormA fast enough for the second click to be queued before the form is hidden, it would open two instances of FormC. When closing one of the instances, FormA would be shown.

You can prevent multiple instances of FormC to be opened:

private void UserSelection_Click() {
   if (!m_ClassB.FormCIsOpen) {
      m_ClassB.method1();
      if (m_ClassB.FormCIsOpen) {
         Hide();
      }
   }
}

---
single minded; short sighted; long gone;

theFrenchHornet14-Jun-07 3:25

14-Jun-07 3:25

This is a very good theory - especially from the excerpt I put out. I had greatly simplified UserSelection_Click. The selection comes from a VS 2003 data grid - the code is determining a double click based on MouseUp, etc. Things stop, i.e., the clock doesn't start for a second double click, until method1 has completed, so I don't think this is exactly the problem. Maybe something similar to what you are describing is happening earlier in the pipe, though. I just haven't been able to find it yet. And, your code suggestion is good to put in as a fail-safe. If nothing else, if the problem pops up again with this code in, then it will narrow down the possibilities some more. Thanks.

theFrenchHornet1-Jul-07 7:29

How to change the (DevExpress .NET v7.1) checkedit's ForeColor?

1-Jul-07 7:29

Fix turned out to be:
Application.DoEvents();
Hide();

Caching data

AndrusM12-Jun-07 5:51

AndrusM

12-Jun-07 5:51

I'm creating C# WinForms client-server database application.
This application reads data from PostgreSQL server using npgsql Dataadapter and DataReader classes and stores data mostly in Datasets and sometimes in business object properties.

A lot of lookup tables (payment terms, currency list etc) are static.
Currently application reads them from server always over TCP connection.

This makes application slow.

How to cache data in client side ?
Where to find caching module for .NET application ?

It it reasonable to use .NET 2 Web Cache object for this ?
Web Cache object doc says that it is designed only for ASP .NET application.
Is it reasonable to use it in WinForms application or are there better
caching object available.

I cannot use MS Caching application block since my application needs to run in
Linux also.

Andrus

Re: Caching data

Colin Angus Mackay12-Jun-07 5:59

Colin Angus Mackay

12-Jun-07 5:59

AndrusM wrote:
How to cache data in client side ?
Where to find caching module for .NET application ?

Have you looked at the Enterprise Library?

AndrusM wrote:
I cannot use MS Caching application block since my application needs to run in
Linux also

I take it that it doesn't compile in Mono then?

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Re: Caching data

AndrusM12-Jun-07 6:41

AndrusM

12-Jun-07 6:41

I this I can compile in under MONO since this is open source.
However Microsoft licence prohibits its using on non-windows environment.

Is it reasonable to use AppDomain cache:

AppDomain.CurrentDomain.SetData("key", value);<br />
DataSet ds = (DataSet)AppDomain.CurrentDomain.GetData("keyname");<br />

or are there any better soluton ?

Andrus

sichensoft12-Jun-07 5:13

sichensoft

12-Jun-07 5:13

We know the label in DevExpress .NET v7.1 controls can change its forecolor augomatic when the skin changed.But I found that the checkedit can not change its forecolor augomatic when the skin changed.

My question is How to change the checkedit's forecolor augomatic when the skin changed.

Thanks a lot!

Re: How to change the (DevExpress .NET v7.1) checkedit's ForeColor?

Colin Angus Mackay12-Jun-07 5:17

Colin Angus Mackay

12-Jun-07 5:17

You are seeking assistance with a third party tool. DevExpress has their own support forums, you should seek assistance there.

Here are the forums: http://www.devexpress.com/Support/Forums.xml[^]

how to cast string with characters to int

Bahaa Hany12-Jun-07 4:22

Bahaa Hany

12-Jun-07 4:22

Hi plz if anyone can help
this is the code
{
string str = "bahaa";
int result = Convert.ToInt32(x);
}
it gives an exception "Input string was not in a correct format."

Luc Pattyn12-Jun-07 4:25

12-Jun-07 4:25

??
there is something wrong I think.
Convert.ToInt32() normally takes a string; I dont know what x is.
if you meant Convert.ToInt32(str);
then obviously that would fail because str does not look like a number at all.

Smile | :)

Luc Pattyn

[My Articles] [Forum Guidelines]

Bahaa Hany12-Jun-07 4:36

Bahaa Hany

12-Jun-07 4:36

yes that what i meant but can't i change it to assci code

Luc Pattyn12-Jun-07 4:59

12-Jun-07 4:59

Convert.ToInt32() expects a string that represents an integer, such as "123" in which case
it would return 123

if you want the integer value of an ASCII character you could do something like:

string str="bahaa";
char c=str[0]; // gets first char
int i=(int)c;

Luc Pattyn

[My Articles] [Forum Guidelines]

Guffa14-Jun-07 11:27

Guffa

14-Jun-07 11:27

Luc Pattyn wrote:
if you want the integer value of an ASCII character you could do something like:

string str="bahaa";
char c=str[0]; // gets first char
int i=(int)c;

Strictly speaking it's not at all an ASCII character, it's a Unicode character, as strings in .NET are Unicode, not ASCII.

---
single minded; short sighted; long gone;

Luc Pattyn14-Jun-07 12:07

C# Member initialization question

14-Jun-07 12:07

Right.
I should have written "if you want the integer value of a character ..."

Smile | :)

Luc Pattyn

[My Articles] [Forum Guidelines]

jayart12-Jun-07 4:12

jayart

12-Jun-07 4:12

Hi All,
What is difference between these two initializations of _obj:
1)

<br />
public class Class1<br />
{<br />
	public Class1()<br />
	{<br />
		//<br />
		// constructor logic here<br />
		//<br />
	}<br />
    private Class2 _obj = null;<br />
}<br />

<br />
public class Class1<br />
{<br />
	public Class1()<br />
	{<br />
		//<br />
		// constructor logic here<br />
		//<br />
                _obj = null; // initialization inside constructor<br />
<br />
	}<br />
    private Class2 _obj = null;<br />
}<br />

Would there be difference between 1) and 2), if Class2 is a class from another referenced dll?

Re: C# Member initialization question

Luc Pattyn12-Jun-07 4:23

Re: C# Member initialization question

12-Jun-07 4:23

Hi,

with your code it is the same because both contain a line
private Class2 _obj = null;
furthermore an object reference is null by default when it is a class member.

There are circumstances where there would be a difference; examples:

1) when _obj has to be initialized to something other than null, and its value is
required before an object of Class1 is being instantiated (maybe its needed by some
public static methods/properties).

2) when the constructor would fail (throw an exception) and hence not reach the
initialization statement.

Smile | :)

Luc Pattyn

[My Articles] [Forum Guidelines]

jayart12-Jun-07 4:43

jayart

12-Jun-07 4:43

Me too thought that the initilizations in 1) and 2) were same.
But I had a problem in Design mode when 2) was used.
I could solve the problem when 1) was used instead.
I am just too confused. I dotn find any reason why it behaves differntly.

Let me explain in deatil.
MyClass1 is a UserControl class. MyClass1 is to be used in frmMain (Main Form)class.
MyClass2 is a class in another dll which is referenced in the project and used in MyClass1.

I have two Confusions:
Confusion-A) The designer of MyClass1 opens fine even if 1) or 2) is used.
Confusion-B) assuming I use method 2) - When I try to add the UserControl class MyClass1 in the designer of frmMain, I get an error that it could not add the control. Mysteriously enough if I use method 1) instead, everything worked fine.

Since MyClass2 is in another dll, would it initialize it differently if initialized in constructor or while declaring it?
Note: Both ways the _obj is initialized as null.

Re: C# Member initialization question

Luc Pattyn12-Jun-07 5:09