List<> remove item issue

We are using List<object> type as datasource for dropdownlist.

Process flow:

1. Assign value (List<objec开发者_如何学运维t>) to the session in the pageload event(!ispostback).
2. Retrieve value from session in ddl_SelectedIndexChanged event
3. Remove a particular item from the list and bind to the ddl

Code:

List<Loc> locList = new List<Loc>();
locList =  (List<Loc>)Session["Loc"];
locID = "xxx";

locList.RemoveAt(locList.FindIndex(FindLocation));

Problem:

Item is getting removed from the base source also (session).

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The problem is that you're manipulating the list that is stored in the session, not a copy. Instead, if you do something like this:

List<Loc> locList = new List<Loc>((List<Loc>)Session["Loc"]);
locID = "xxx";

locList.RemoveAt(locList.FindIndex(FindLocation));

you're operating on a copy of the list, and the original won't change.

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It sounds like you are storing the list in session, fetching it out, and mutating it. Actually, you might see different results if you switch from the in-process state to distributed state or database state.

The problem is that with in-process state there is only one list. It isn't serialized / deserialized, so when you remove an item it stays removed. You could clone the list easily enough:

locList = new List<Loc>(locList);

which should solve this. With the other state implementations the data is serialized, and each deserialized copy is separate, so you won't see this. But I wouldn't depend on the state implementation. Personally I've never understood why such behaviour-changing subtleties are allowed with state; I would have preferred it to always serialize/deserialize, even when in-process.