How can items in collection get collection count?How can items in collection get collection count?
Old forum URL: forums.lhotka.net/forums/t/4324.aspx
meierk posted on Saturday, February 09, 2008
I have a need for each item in my BusinessListBase to know how many items are in the collection, but I must be having a brain fart because the solution is eluding me.
I tried iterating through the list in my BusinessListBase and setting a count property immediately after the collection has been loaded, but that puts the collection into a Dirty state, and I don't want that behavior either.
I would greatly appreciate any help with this.
Thx,
Kevin
meierk replied on Saturday, February 09, 2008
Ok, brain started working again. I just removed the call to PropertyHasChanged to state doesn't become dirty. Still be interested in a better way to achieve this without having to interate over the list.
Kevin
Marjon1 replied on Saturday, February 09, 2008
Kevin,
There are three possible solutions that I can see off the top of my head:
- I assume you are using a property to set the count property; this would then call PropertyHasChanged. Is this necessary? Is this information only used by the business object or does the addition of a new item make all other items dirty? If not remove the PropertyHasChanged event.
- Can you retrieve the number of records from whatever source you are reading from and put this as part of the fetch? Changes to this would work somewhat like you are now.
- If this is even possible I have no idea, I haven't used the parent property for anything yet.
You could change the count property on the item to refer to it's parent and try and cast it to the correct list type and then refer to the count from that. In this way you wouldn't need to retrieve or update it. If this is possible, I'm not sure but if it was would be the way that I'd do it.
skagen00 replied on Saturday, February 09, 2008
You can absolutely use the parent reference and cast it to the type of the collection object to get the count.
But I would be really interested in what your use case is for this, because it seems odd to me that a child would need to know the number of items in the collection.
Chris
meierk replied on Sunday, February 10, 2008
Thanks for the replies.
I actually did remove the call to PropertyHasChanged, however, this has a small performance hit since I am loading the collection and then reinteracting over it again. Normally a small performance hit wouldn't be an issue, but because of the design of the interface, this hit is incurred often. In addition, this application is a rewrite of an existing Delphi application which is very fast so when the users saw the prototype they were a little disappointed.
As for the use case, I actually have two.
1) The child collection is edited in a grid. When the user changes the value in one of the columns, a calculated column is updated. That calculated column has a calculation that requires total number of rows in the child collection. The calculation is performed in the setter of the property that the user edited.
2) I have a collection of rows where the first column is labeled "Location" with a sequential number from 0 through n. When the data is displayed in the grid I need the first row (location 0) to read "Lead Tan" instead of "0". I also need the last row to say "Lag Tan". The way I approached this was to create a readonly property in my child to display the proper value, but when I originally created this property there was a rule that fixed the number of rows to 9. Now the number of rows is variable so I
need a way of determining the max location value.
Sorry for the lengthy explainations, but I'm trying to avoid a having solutions provided without the appropriate background information. Is there a better way to design this? I'm sure there is, but I am plagued with learning C# and CSLA at the same time and I am restricted by the fact that I have to work with a database that I cannot change and a UI that absolutely has to match the old Delphi app. I have some flexibility with behavior, just not the actual layout of the UI.
Thanks,
Kevin
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