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Hi Gareth,
no problem!
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Hi!
I am using MS Visio control in an application developed in C# (for .Net 1.1). I have a class MyAppContext that extends ApplicationContext. The application is started by calling Application.Run(myAppContext) where myAppContext is an instance of class MyAppContext.
The problem I face, is this, only under Vista, if a form containing Visio control is initialized, a NullRefrenceException is thrown. However, if I load the same form before initializing myAppContext, it works fine.
The same code works under XP and Windows 2003. I have also used 'Run as Administrator' option in Vista but the result is same.
Does anyone have a clue, what should I do to fix this problem?
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Kashif Iqbal Khan wrote: a NullRefrenceException is thrown
by whom? at what line? catch the exception, look at its ToString() output, tell
Visual Studio to always show line numbers, and identify the faulty line.
A wild guess: you did something that is not thread-safe, your XP machine is single core
so it runs fine nevertheless, and your Vista machine is dual core, so it is bound to fail.
As I said, this is just a guess.
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Thanks for your prompt reply.
The exception stack trace shows that it is thrown somewhere in AxHost class. Unfortunately, I am not at my work place right now, so cannot attach the exact StackTrace. But will update as soon as I get it.
To explain further, I am writing the code flow that is something like as follows
<br />
<br />
VisioForm f = new VisioForm();<br />
f.Show();<br />
f.Close();<br />
<br />
MyApplicationContext c = new MyApplicationContext; <br />
Application.Run( c );<br />
<br />
<br />
There is a button on MainForm that has the same code as mentioned in Line 1-3 above in its click event. Now If I comment the code as in Line 1-3, the application will crash if the button on main form is clicked. But works fine, if I leave it there.
More interestingly, If the lines 1-3 are moved between line 4 and 5, the application will still crash with the same message.
This makes me believe that there is something wrong when using ActiveX controls inside a custom application context on Vista.
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Hi,
I have some remarks, not sure how relevant they are:
1. are you sure about your f.Show f.Close sequence? it shows then hides the form, without
waiting for anything? or did you mean ShowDialog()?
2. I would put everything in one big try-catch as in:
try {
... all about VisioForm
... all about MyApplicationContext
} catch(Exception exc) {
Console.WriteLine(exc.ToString());
}
that will catch everything in the main thread that you may have forgotten to catch
elsewhere. Note the ToString, it is important to see the entire exception.
3.
Are you manipulating apartment models? is everything STAThread? MTAThread?
Maybe the Visio stuff needs it to be STAThread. I don't know the details, I do know
it often is an issue when using COM.
4.
Are you using the same version of Visio on both machines?
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Thanks for all your effort.
1. Yes, it is form.Show() and form.Close(). This is actually a work around to make the application work on Vista. After placing these lines, VisioForm opens fine whenever the button on MainForm is clicked.
2. The code does has try-catch. Problem is I cannot get my form open. I will put the exception log here.
3. Main module has STA Attribute.
4. Yes.
Actually if I open and close the form containing Visio control (Line 1-3 in my previous post), before application context initialization, my application works fine on Vista. but If I remove these lines, it starts crashing whenever the VisioForm is initialized.
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Hi Guys. I have an opendiledialoge. If I click Cancel then the whole project closses. Any idea how I can set it to return to the main form if the user clicks on cancel instead of having the whole app closing??
Here is the code.
if (openFileDialog1.ShowDialog() != DialogResult.OK)
{
this.Close();
}
Excellence is doing ordinary things extraordinarily well.
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I have solved it.
I set it as follows:
if (openFileDialog1.ShowDialog() != DialogResult.OK)
{
return;
}
Excellence is doing ordinary things extraordinarily well.
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Ah, that was a good laugh.
"I told my app to close, and it closes; but I don't want it to close, how do I get it not to close? (Help urgent please)" 
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He figured it out and fixed it. Obviously not a Hlp Urgnt Pls at all, just a beginner. Just like you and I were
Jon
Smith & Wesson: The original point and click interface
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Oh I wasn't laughing at him in particular. 
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Hi,
You can use the below also.
if (openFileDialog1.ShowDialog() == DialogResult.Cancel)
return;
Regards,
Charith
Charith Jayasundara
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Hi,
IMO the best way is by testing for a positive, as in:
if (openFileDialog1.ShowDialog() == DialogResult.OK) {
} }
That way, if for whatever reason something other than OK and Cancel gets returned,
nothing will happen.
I tend to avoid negative tests, they tend to confuse people sometimes.
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Hi Luc. I used to have it that way but then for some reason the openfiledialog would show again if you selected the file and clicked on OK. When I changed it to a negative test then it worked fine.
Thanks for taking the time to help and reply. It is greatly appreciated. Someday I will be able to help the guys out as well and be a great programmer like most of the guys here.
Excellence is doing ordinary things extraordinarily well.
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Hi,
Kwagga wrote: for some reason the openfiledialog would show again
Seeing the dialog more than once cannot depend on how you formulate the condition;
it would need either a loop (for, while, ...) or the method being called more than once.
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This is code from another project I am working on. This is where the openfiledialoge is opened twice instean of once.
private void btnOpenFix_Click(object sender, EventArgs e)
{
if (openFileDialog1.ShowDialog() == DialogResult.OK)
{
txtboxFixed.Text = openFileDialog1.FileName;
}
if (openFileDialog1.ShowDialog() == DialogResult.Cancel)
this.Close();
Now that I know how to resolve this in one code statement I can fix it.
So, I would rather have it like this:
private void btnOpenFix_Click(object sender, EventArgs e)
{
if (openFileDialog1.ShowDialog() != DialogResult.OK)
{
return;
}
else
txtboxFixed.Text = openFileDialog1.FileName;
}
Excellence is doing ordinary things extraordinarily well.
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Ah, see? You're calling ShowDialog twice.
You could store the result in a local variable:
DialogResult res = openFileDialog1.ShowDialog() ;
if ( res == DialogResult.OK ) ... ;
if ( res == DialogResult.Cancel ) ... ;
or use a switch:
switch ( openFileDialog1.ShowDialog() )
{
case DialogResult.OK : ... ; break ;
case DialogResult.Cancel : ... ; break ;
}
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Hi,
adding to what PIEBALD told you, I find it rather strange that your program would
do something when CANCEL is clicked; normally cancel means "don't do anything, since I have
changed my mind". This also means you should NOT close the form itself.
I trust the above is part of the Microsoft recommendations for a Graphical User Interface.
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Hi all,
I used this code for computing total price<b></b> of all item that customer ordered them:
public Double total <br />
{<br />
get<br />
{<br />
double t;<br />
if (items == null)<br />
{<br />
return 0;<br />
}<br />
foreach (cartitem Item in items)<br />
{<br />
t += Item.Totalline;<br />
}<br />
return t;<br />
}<br />
}but this error occured when i run above code:
Use unassigned local variable 't'
Now where i should define 't'?
Hoda
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Hoda,
The line
<br />
double t; <br />
should be changed to:
<br />
double t = 0;<br />
You need a default value. The first iteration of your foreach statement is trying to add a double value to null which doesn't work. So give 'er a default value and be off
Hogan
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Dear Hogan,
thank you very much for you response.
Hoda
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I am developing an application where multiple users will have concurrent access to a database for reads, writes/adds, deletes and updates. Much of the user interface will be through the DataGridView control. I am trying to come up with as elegant a solution as possible to dynamically update a DataGridView for, say, User #2 if User #1 makes a database change to the same table that User #2 is viewing. It seems that I have to programatically refresh the grid no matter how I have it bound to the database (connected or disconnected recordsets). Am I missing something? Is there something in ADO.Net that will enable me to bind data to a grid such that any changes to the database will almost immediately be reflected in the grid with no forced/programmatic refresh?
Thank you...
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No There is no such facility. The closest thing to what you want is SQL Server Notifications, but that is cumbersome and overkill here.
Your idea to update user1 of changes by user2 may not be as good a design as you think. Some questions to consider:
1. How likely is it that multiple users will be modifying the same data?
2. What is the likelyhood they will be viewing the same data (same subset of rows in the same table).
3. If user1 edites field A of row 2 just as your update notification arrives for User B having done the same, what will you do - overwrite user1's change? how annoying might that be?
In most cases both 1 and 2 are relatively rare, so all the network round trips needed to even determine if users need to be synchronized is not worth the negative impact on performance and scalability. The normal practice here is to detect collisions only when the user commits changes, and refuse them if the modified data had additional changes after the first user read them, but before he posted changes (typically by adding a timestamp field to each row, and comparing the timestamps - only allow update if they are still equal).
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