Re: ObservableCollection Constructor - C# Discussion Boards

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)

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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Michael Sync11-Jan-09 7:21

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)

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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Michael Sync11-Jan-09 8:45

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)

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#]
_____________________________
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User 665811-Jan-09 7:51

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.

Michael Sync11-Jan-09 8:45

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)

Michael Sync12-Jan-09 4:49

List<T>.AddRange and ArgumentException?

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)

User 665811-Jan-09 4:05

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.

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

only two letters away from being an asset

User 665811-Jan-09 4:26

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.

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

User 665811-Jan-09 4:52

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.

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.

User 665811-Jan-09 4:56

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.

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.

User 665811-Jan-09 6:48

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.

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.

User 665811-Jan-09 8:18