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Why do you clear the table in the first place? I take it you're updating your containing DataSet using a DataAdapter derivative? If so, the table gets is not referenced when you 'new-up' another DataSet. You could just set DataGrid.DataSource to null.
Debug your code and see on what line (or after what line, since you're clearly not in the stack trace) or with what action this exception actually happens. This is common, for example, when you insert a new row into the DataGrid then update your data source using DataAdapter.Update. Your SQL INSERT statement (the DataAdapter.InsertCommand) should be a compound statement with a SELECT after it to re-select the data you just inserted (using the wizard, VS.NET will do this for you) so that you get the right keys (important with identity columns and incremental columns - your basic PK fields). But you don't seem to be doing that so I'm a little confused. The other information I requested above may help.
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Software Design Engineer
Developer Division Sustained Engineering
Microsoft
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Heath Stewart wrote:
I take it you're updating your containing DataSet using a DataAdapter derivative?
No. I'm enumerating the rows in the DataTable and updating the database manually because the data presented to the user is not exactly the same as in the database (not a perfect design, I know, but no time to change it now.)
When a sale is registered, all the controls are set to disabled state, and the DataGrid to read only, which allows the cashier to review the sale, and either cancel it or start a new one.
I have a button labeled Clear Sale that when clicked should clear the table (and the other controls, as well as enabling them) Setting a breakpoint at the very first line of the handler for that button's Click event is worthless, since the exception is thrown before, as the DataGrid is losing focus (clicking on another control proves this.)
After I click Continue on the exception dialog, nothing happens. And when I click that Clear Sale button again, everything works as expected.
The only difference I can see between the first and second clicks on the Clear Sale button is that the empty row (for add new record) isn't displayed the second time.
First time (before the exception):
http://www.luisalonsoramos.com/ww1.jpg[^]
Second time (after the exception):
http://www.luisalonsoramos.com/ww2.jpg[^]
What do you think?
Thanks in advance!!
-- LuisR
Luis Alonso Ramos
Intelectix - Chihuahua, Mexico
Not much here: My CP Blog!
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Luis Alonso Ramos wrote:
No. I'm enumerating the rows in the DataTable and updating the database manually because the data presented to the user is not exactly the same as in the database (not a perfect design, I know, but no time to change it now.)
That's what views and stored procedures are for.
Luis Alonso Ramos wrote:
What do you think?
There's a lot of things this could be. One thing you could do is create a strongly typed DataSet in the designer and set the PK DataColumn to auto-increment or something. You can also do this programmatically yourself if you don't want to define a new type (that's much easier, IMO). That way when a new row is created it will have a unique PK. If - while enumerating the rows and updating the database yourself - you don't want to use that PK (and you probably won't) then fine. But it's existence is there for when the DataGrid validates the data (which happens when the row is committed, which is, eseentially, when it loses focus - which of course happens when the DataGrid loses focus).
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles] [My Blog]
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Thanks for your quick reply (as always!).
I'm going to add that PK you mention, but in the meantime, I'll give you some more facts:
* I can trap the exception if I derive my own DataGrid and override the OnLeave handler. When I get the exception, the Click event for the Button never arrives. If I give the focus again (after the exception) to the DataGrid (by clicking on it) and click again the Clear Sale button, the Click event for the Button doesn't arrive either, but this time I get no exception.
* If, before calling the base class, I remove set ReadOnly to false, I get no exception, but still the Click event for the Button is swallowed.
* When the user adds a record to the table, and then deletes it (or if he types an erroneous product code, the row is deleted programatically), the record is still somehow in the table with the status set to Deleted (or Detached, would you explain me the difference?). This was giving me trouble until I found that out, and when enumerating the records, I skip Deleted and Detached records.
* I still get the exception if there are Deleted or Detached rows only (if I type a wrong product code, and then leave the table empty.)
Heath Stewart wrote:
That's what views and stored procedures are for.
I know. I've learnt a lot about SQL Server and ADO.NET recently, but when I started this project, I hadn't read as many books! 
Thanks again,
-- LuisR
EDIT: I added the primary key to my DataTable, I still get the exception.
Luis Alonso Ramos
Intelectix - Chihuahua, Mexico
Not much here: My CP Blog!
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Luis Alonso Ramos wrote:
the record is still somehow in the table with the status set to Deleted (or Detached, would you explain me the difference?).
As I always say, read the documentation: http://msdn.microsoft.com/library/en-us/cpref/html/frlrfSystemDataDataRowStateClassTopic.asp[^]. It's these sort of simple questions ("What does X do?") that are easily answered by the documentation.
If you want to get the changes that have been made to the underlying DataSet, use DataSet.GetChanges (optionally specifying the types of changes you want to get).
Luis Alonso Ramos wrote:
I know. I've learnt a lot about SQL Server and ADO.NET recently, but when I started this project, I hadn't read as many books!
I've read almost no books (and I usually skim the once I do evaluate or read). Reading the documentation is essential. Digging into the implementation (since managed languages compile to Intermediate Language (IL), you can easily read them using ildasm.exe (from the .NET Framework SDK) or .NET Reflector (a decompiler and disassembler). Digging into the DataGrid and its related classes (like how it uses DataGridTableStyles and DataGridColumnStyles can really help understand how it works.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles] [My Blog]
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Heath Stewart wrote:
I've read almost no books
I find books useful, not to teach how to do something, but to tell me that something exists in the first place. Most times I read books and learn about something and then forget, and whenever there's a need for that feature, I remember and then go search in the docs (or in the book.) It's just not good when you face a problem, and solve it somehow with a thousand lines of code, when there was this class that you could have used and achieved the same result with just fifty lines.
This app I'm fixing right now was my first Windows Forms application, so there are a lot of things I would do different if I were to rewrite it.
Heath Stewart wrote:
.NET Reflector (a decompiler and disassembler)
Great tool!! Finding it was worth the day!! 
At least I found exactly where my exception is coming from. Tomorrow I'll try to find a workaround!
Once again, thank you very much for your time,
-- LuisR
Luis Alonso Ramos
Intelectix - Chihuahua, Mexico
Not much here: My CP Blog!
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Luis Alonso Ramos wrote:
I find books useful, not to teach how to do something, but to tell me that something exists in the first place.
How is reading page after page of something that typically only covers one subject (like Windows Forms, ASP.NET, .NET Remoting, etc.) any easier or faster than browsing the class library? You'll learn much more that way - perhaps even more than the book author (writing a book doesn't necessarily make you an expert, nor could you possibly cover the hundreds of classes that exist in the BCL - and that number keeps growing with each version).
You can learn even more than books can tell you by learning and understanding IL, the CLI, and the other technologies that comprise the .NET Framework. I know exactly how most classes work in the BCL (the ones I've reviewed, anyway) and a book won't tell you that. They typically only cover how to use a class - not how it works.
Also making the articles on http://msdn.microsoft.com/library[^] daily reading is beneficial. You'll read articles from Microsofties and third-parties alike and it's all free. Many of these authors are even authors of books that you may have read. You can also pick up the Patterns and Practices PDFs (same content as the books) for free from http://msdn.microsoft.com/patterns[^], where these hard-cover books typically cost between $40 and $50 (USD). They're not really books, though, they're references that go deeper into a technology than a "how-to" book.
If books work for you, great - to each his own. But don't discount the importance of understanding how things work and reading the documentation for classes, members, etc. because a book typically won't go into that much detail (unless you waste your money on the class library reference book, which is just a printed copy of the free .NET Framework SDK that you can download from http://msdn.microsoft.com/netframework[^]).
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles] [My Blog]
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Heath Stewart wrote:
How is reading page after page of something that typically only covers one subject any easier or faster than browsing the class library?
I believe it's a bit easier, since the author takes you between related topics in order. I know the only way to become an expert is to use the technology and learn how it works, and no book will give you that (maybe a Windows Internals-type book but those are hard to find and still not deep enough in every area.) But still reading introductory texts can help you get started, and on the right track for doing additional research.
Heath Stewart wrote:
But don't discount the importance of understanding how things work and reading the documentation for classes, members, etc. because a book typically won't go into that much detail
Of course I know of its importance. But for example, if I want to get data from a database, I would have to know about DataSets and DataAdapters and DataReaders (at least of their existance) and then serach for them in the docs. But a book may introduce me to those, and even tell me when each might be better. Then, of course, I would go to the docs to find more about each object and how to use it to its full potential.
Heath Stewart wrote:
If books work for you, great - to each his own.
Don't think of me as that one who buys 5 or 6 books everytime I go to the bookstore. I really own very few programming books for a specific technology (say ASP.NET or Windows Forms.) Petzold's Programming Windows with C#, Prosise's Programming Microsoft .NET, Sceppa's Programming ADO.NET and Tom's Inside C#, and that's about it (for recent books.)
But still, reading those can give you a broad idea of everything (or most things) the BCL has to offer. I don't pretend to be an expert in everything (you can't nowadays.) But when I need something I don't throughly understand, it's time to dive into the class library documentation.
-- LuisR
Luis Alonso Ramos
Intelectix - Chihuahua, Mexico
Not much here: My CP Blog!
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Luis Alonso Ramos wrote:
But for example, if I want to get data from a database, I would have to know about DataSets and DataAdapters and DataReaders (at least of their existance) and then serach for them in the docs.
That's what the table of contents (TOC) is for. When I first started developing for the .NET Framework (back in 1.0 beta 1) I expanded the TOC namespace by namespace and took a glimpse at the available namespace members. Even if you don't have a great memory, most people would at least get a feeling of deja vu if you required a class to do something.
The point I'm trying to make in this instance is that your specific problem could be understood and fixed if you did understand how the DataGrid works (for example; you don't need a DataSet or DataTable - just an IList or IListSource implementation - so the question becomes "How does the DataGrid bind to lists?"), especially when it comes to defined DataSets (those with explicit table and column definitions). Unfortunately - not knowing your implementation well enough - I can't help as much, but I can at least give you ideas about how to fix it. If you were to dig into the IL disassembly (or decompile using .NET Reflector - but learning IL really is helpful) it would most likely help in figuring out how to work around your particular problem.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles] [My Blog]
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Heath Stewart wrote:
Unfortunately - not knowing your implementation well enough - I can't help as much, but I can at least give you ideas about how to fix it
I think I've fixed it. The problem is that when I set the DataGrid to read only, the add-new-record row is removed. During the OnLeave_grid (private, called by DataGrid's OnLeave handler), if the control is read only, it tries to create a new AddNewRow at the very end (don't ask me why.) See the following code (from .NET Reflector):
if (this.gridState[0x100000])
{
this.listManager.CancelCurrentEdit();
DataGridRow[] rowArray1 = this.DataGridRows;
rowArray1[this.DataGridRowsLength - 1] = new DataGridAddNewRow(this, this.myGridTable, this.DataGridRowsLength - 1);
this.SetDataGridRows(rowArray1, this.DataGridRowsLength);
}And since the DataTable does not contain any rows, the exception is thrown for accessing index -1.
I wanted to set the DataGrid to read only instead of disabling it, so the user could scroll to review sales, and also to remove the add new row. My fix was to disable the DataGrid if it contains no records (the add new row is still displayed), or make it read only otherwise. That fixed the problem.
Thank you very much for all your help,
-- LuisR
Luis Alonso Ramos
Intelectix - Chihuahua, Mexico
Not much here: My CP Blog!
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Hi, is there any way to trigger an event on a minute change with a DateTime object or something like that?
I would like my program to be noticed when the computer's clock changes. I don't want to do it with a Timer object because it is not synchronized with the PC's clock.
Thanks!
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The computers clock is changing constantly! What are you trying to do?
Are your trying to get notified of a USER change to the system clock? No event like this exists...
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Actually, there is: Microsoft.Win32.SystemEvents.TimeChanged.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
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Doh 
So there is! It'll be 2010 before I remember that namespace exists!
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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No, I want to get notified every minute!
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This isn't the forum for that (it's a not a C#/.NET problem). Ask in either the Operating Systems directory or visit the Microsoft newsgroups at http://msdn.microsoft.com/newsgroups/[^].
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles] [My Blog]
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I have a request from a client who wishes to use either the Enter Key or the Arrow Key, as well as the Tab key, to move from field to field in a Windows Form.
Is it possible?
Fred S. Parker
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Yes. Look into KeyPreview, OnKeyPress, and TabIndex.
KeyPreview instructs the framework to send you the keys pressed on the form. OnKeyPress will allow you to see what key is pressed. TabIndex will help you determine which control to give focus to.
This posting is provided "AS IS" with no warranties, and confers no rights.
Alex Korchemniy
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Instead of walking the tab indexes yourself, just use the Control.GetNextControl method like so in your Form:
if (ActiveControl != null)
ActiveControl.GetNextControl(ActiveControl, true); Use can pass false to the second param to go backward. You should do this when the shift key is down.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles] [My Blog]
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* ducks *
Probably overslept a little too much 
Alex Korchemniy
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We can use these methods,such as ZeroMemory() and memcpy() in VC++ to manage memory,so what about those matters in C#?
Thanks!
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Since C# runs in a MANAGED execution environment, these functions are pretty much useless. If you create a new array, the memory is automatically zero'd out. Copying memory is not exactly a feasible operation because of the nature of how objects can be stored in memory. It's always better to use the objects Copy() or Clone() methods, if they support it.
There are always ways to duplicate the functionality to you need in C# other than using the shortcuts these functions provide to C++.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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get it.
^_^Thanks!
Good luck!
momer
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is there anything like ShellExecute in C# to launch other applications?
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