Re: ObservableCollection Constructor - C# Discussion Boards

Re: Password protect information in an application

Not Active11-Jan-09 8:30

11-Jan-09 8:30

Add login to the application and check the credentials when displaying the dialog. It isn't that difficult and there are plenty of examples here and elsewhere. What have you tried so far?

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Help Creating Sql Class

Calferreira11-Jan-09 7:06

Calferreira

11-Jan-09 7:06

Hi there , i'm trying to create a class in C# to use my Sql operations but i'm facing some problems.
Although i'm using the code to import SQL objects(using system.data.sqlclient;) i can't declare variables such as Sqlcommand or sqlclient for ex.That way the class get's kind meaningless.How can i use them?

Thanks for your help and pacience as you will figure it out i'm learning C# i was a Vb6 coder.

Re: Help Creating Sql Class

User 665811-Jan-09 7:41

User 6658

11-Jan-09 7:41

You mean the compiler doesn't find the SqlCommand and other types? You need to add a reference to the System.Data.dll. In Visual Studio right click on the project and select "Add Reference".

regards

modified 12-Sep-18 21:01pm.

Re: Help Creating Sql Class

Calferreira11-Jan-09 8:09

Calferreira

11-Jan-09 8:09

Already done that.
You can see better here http://img171.imageshack.us/my.php?image=screenshotvz3.jpg[^]

Re: Help Creating Sql Class

User 665811-Jan-09 8:14

User 6658

11-Jan-09 8:14

You also have to import the namespace (also just typing SqlCommand into the editor VS will automatically suggest you to import the necessary namespace):

http://msdn.microsoft.com/de-de/library/system.data.sqlclient.sqlcommand(VS.80).aspx[^]

using System.Data.SqlClient;

modified 12-Sep-18 21:01pm.

Re: Help Creating Sql Class

Calferreira11-Jan-09 10:59

Calferreira

11-Jan-09 10:59

Thanks!

ObservableCollection Constructor

Michael Sync11-Jan-09 6:20

Michael Sync

11-Jan-09 6:20

I'm facing some problems with ObservableCollection constructor..

Any idea why this code is not working?

entity.Currencies = new ObservableCollection<CurrencyEntity>(CurreniesList.Where( c => c.IsSelected));

Note:

1. entity.Currencies is ObservableCollection<CurrencyEntity>().
2. CurrenciesList is ObservableCollection<CurrencyEntity>().
3. CurrencyEntity class has a proprety called "IsSelected".

Thanks in advance.

Thanks and Regards,
Michael Sync ( Blog: http://michaelsync.net)

Re: ObservableCollection Constructor

S. Senthil Kumar11-Jan-09 6:40

S. Senthil Kumar

11-Jan-09 6:40

ObservableCollection < T > 's constructor takes a List < T >, and not IEnumerable < T >, presumably because only then can it "observe" addition and removal of elements. Simply wrapping the result of CurrenciesList.Where in a list should solve the problem.

new ObservableCollection <CurrencyEntity>(
                new List<CurrencyEntity>(currenciesList.Where(c => c.IsSelected)));

Regards
Senthil [MVP - Visual C#]
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Re: ObservableCollection Constructor

Michael Sync11-Jan-09 7:21

Michael Sync

11-Jan-09 7:21

Hi Senthil,

Thanks but I'm still getting the error. There are 3 constructors[^] in ObservableCollection.

IEnumerable[^] is one of them.

Or, Am I missing something??

Thanks and Regards,
Michael Sync ( Blog: http://michaelsync.net)

Re: ObservableCollection Constructor

S. Senthil Kumar11-Jan-09 8:24

S. Senthil Kumar

11-Jan-09 8:24

My bad, I missed out the third overload.

Can you paste the error that you are getting?

[EDIT] .NET 3.0 has only two overloads (http://msdn.microsoft.com/en-us/library/ms658737(VS.85).aspx[^])

Regards
Senthil [MVP - Visual C#]
_____________________________
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Re: ObservableCollection Constructor

Michael Sync11-Jan-09 8:45

Michael Sync

11-Jan-09 8:45

The error message is like it doesn't a constructor that takes 1 argument.

I'm using 3.5.... Am i referencing the wrong dll or need to import some namespaces? it's very strange

Thanks and Regards,
Michael Sync ( Blog: http://michaelsync.net)

Re: ObservableCollection Constructor

S. Senthil Kumar11-Jan-09 8:58

S. Senthil Kumar

11-Jan-09 8:58

What does hitting F12 (Go to Definition) on the ObservableCollection show?

Regards
Senthil [MVP - Visual C#]
_____________________________
My Home Page |My Blog | My Articles | My Flickr | WinMacro

Re: ObservableCollection Constructor

User 665811-Jan-09 7:51

User 6658

11-Jan-09 7:51

This sounds a bit strange, because this is working for me:

public class CurrencyEntity
{
	public bool IsSelected
	{
		get { return true; }
	}
}

This is just a stub, and here's the code:

List<CurrencyEntity> c1 = new List<CurrencyEntity>() { new CurrencyEntity() };
ObservableCollection<CurrencyEntity> ob = new ObservableCollection<CurrencyEntity>(c1.Where(c => c.IsSelected));

modified 12-Sep-18 21:01pm.

Re: ObservableCollection Constructor

Michael Sync11-Jan-09 8:45

Michael Sync

11-Jan-09 8:45

I will try again and let you know. it's very strange..

Thanks and Regards,
Michael Sync ( Blog: http://michaelsync.net)

Re: ObservableCollection Constructor

Michael Sync12-Jan-09 4:49

Michael Sync

12-Jan-09 4:49

Thanks. I think it doesn't work because of Silverlight. I'm using Prism v2 (with multi-targeting feature). so, i need to create the class in SL project and link that class from wpf. that's why the code doesn't work.

Thanks for your help.

Thanks and Regards,
Michael Sync ( Blog: http://michaelsync.net)

List<T>.AddRange and ArgumentException?

User 665811-Jan-09 4:05

User 6658

11-Jan-09 4:05

Hi everyone,

I'm experiencing a strange exception in the List<T>.AddRange[^] method.
Sometimes (maybe in 1 out of 100 runs with the same data) I get a System.ArgumentException inside AddRange that the destination array is not large enough for the collection. Here's what I'm doing:

if (itemsToAdd > 0)
{
   existingItems.AddRange(itemsToAdd); // boom
   itemsToAdd.Clear();
}

Now MSDN clearly states:

If the new Count (the current Count plus the size of the collection) will be greater than Capacity, the capacity of the List<(Of <(T>)>) is increased by automatically reallocating the internal array to accommodate the new elements, and the existing elements are copied to the new array before the new elements are added.

Did anyone else experience this weird behaviour?

regards

modified 12-Sep-18 21:01pm.

Re: List<T>.AddRange and ArgumentException?

Not Active11-Jan-09 4:16

Not Active

11-Jan-09 4:16

Sounds like it is a problem of the allocation of new memory to expand the collection is slower than expected by the framework. Have you tried to set the expected number of elements when you create the List? You may not have an exact number, but an large estimate should prevent this from occurring. The TrimExcess method can free up any extra resources after you've filled the List

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Re: List<T>.AddRange and ArgumentException?

User 665811-Jan-09 4:26

User 6658

11-Jan-09 4:26

Mark Nischalke wrote:
Have you tried to set the expected number of elements when you create the List?

That's what I will actually try next. But since the error is quite hard to reproduce I'm not sure if this will help. I do have an estimated number how many items the list will contain, so I could set it. It's a very small number of items, so I don't think it's some sort of memory problem (but in this case I think OutOfMemoryException would be the proper one).

modified 12-Sep-18 21:01pm.

Re: List<T>.AddRange and ArgumentException?

Not Active11-Jan-09 4:33

Not Active

11-Jan-09 4:33

I didn't say it was a memory problem per se. If the framework were trying to place a element into the collection before the memory allocation and redistribution had completed, then it would be an ArguementExcepetion, not an OutOfMemoryException.

only two letters away from being an asset

Re: List<T>.AddRange and ArgumentException?

User 665811-Jan-09 4:52

User 6658

11-Jan-09 4:52

This sounds like a valid point. I just wonder if there's something I can do against it apart from setting the capacity myself - but it shouldn't be a real problem, so I think this is fine.

modified 12-Sep-18 21:01pm.

Re: List<T>.AddRange and ArgumentException?

Daniel Grunwald11-Jan-09 4:35

Daniel Grunwald

11-Jan-09 4:35

I can imagine two possible causes:
- existingItems or itemsToAdd is accessed from multiple threads and the item count changes during the insertion.
- itemsToAdd implements the ICollection<T> interface incorrectly. What type is itemsToAdd?

Given that you're getting the exception only in 1 of 100 cases, I'm pretty sure that it's the first case: either existingItems or itemsToAdd is accessed from multiple threads.

Re: List<T>.AddRange and ArgumentException?

User 665811-Jan-09 4:56

User 6658

11-Jan-09 4:56

Daniel Grunwald wrote:
- existingItems or itemsToAdd is accessed from multiple threads and the item count changes during the insertion.

No threads involved (at least none that I know of). However, itemsTooAdd is modified by a different event callback which I have no access to.

Daniel Grunwald wrote:
- itemsToAdd implements the ICollection<t> interface incorrectly. What type is itemsToAdd?

It's also a List<T> of the same type.

modified 12-Sep-18 21:01pm.

Re: List<T>.AddRange and ArgumentException?

Daniel Grunwald11-Jan-09 5:01

Daniel Grunwald

11-Jan-09 5:01

Greeeg wrote:
No threads involved (at least none that I know of). However, itemsTooAdd is modified by a different event callback which I have no access to.

And on which thread does that event callback run?
Try using "System.Diagnostics.Debug.WriteLine(Thread.CurrentThread.ManagedThreadId);" to see if it runs on the same thread as the rest of your code.

If you use AddRange to add a List<T> to another List<T> and get that exception, I'm pretty sure that the event runs on a separate thread or uses the thread pool.

Re: List<T>.AddRange and ArgumentException?

User 665811-Jan-09 6:48

User 6658

11-Jan-09 6:48

Daniel Grunwald wrote:
I'm pretty sure that the event runs on a separate thread or uses the thread pool.

You're right:

TID Normal: 1
TID Event: 16

I guess my only solution is to lock the entitiesToAdd, right?

modified 12-Sep-18 21:01pm.

Re: List<T>.AddRange and ArgumentException?

Guffa11-Jan-09 7:47

Guffa

11-Jan-09 7:47

You can't lock an object, you can only lock code blocks.

You have to use a lock around the code in both threads, using the same object as identifier.

Despite everything, the person most likely to be fooling you next is yourself.

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