Predicates and Lists
I have a generic list.
Some elements of this list belong to a parent element. I retrieved all these elements from a database and i want to recursively build a tree with them.
So, here's what i'm thinking:
Here is my predicate:
public static bool FindChildren(Int32 parentId,CategoryMapping catMapping)
{
if (catMapping.parentId == parentId)
{
return true;
}
else
{
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}
}
root = list[0];
root.childrenElements = root.FindAll(FindChildren(root.id,???)
I can't figure out how this would work. How can i do this kind of predicate?
PS: I'm using VS2005 :(
Try
root.childrenElements =
root
.Where( i => i.parentId == yourCatMapping.parentId)
.ToArray();
EDIT
In .net 2.0 I think it is
root.FindAll(
delegate(CategoryMapping mapping)
{
return mapping.parentId == root.Id;
});
You need to specify a delegate to pass to FindAll
, rather than a direct function call
(assuming root
is List<CategoryMapping>
)
root.childrenElements = root.FindAll(c => FindChildren(root.id, c));
You should check out this thread that I started on Forming good predicate delegates to Find() or FindAll() in a List for C# / .NET 2.0
It answers your question pretty clearly.
Gregoire's answer is the best, because it:
- Doesn't use LINQ (the asker is using VS 2005)
- Doesn't use a lambda expression (again, VS 2005)
That said, why not make things (slightly) easier for yourself by writing a function to generate your Predicate
for you:
public static Predicate<CategoryMapping> GetIsChildOf(int parentId) {
return delegate(CategoryMapping cm) {
return cm.parentId == parentId;
};
}
Then if you have a List<CategoryMapping>
and you want to find all elements with a certain parentId
property, you can just call:
root = list[0];
root.childrenElements = list.FindAll(GetIsChildOf(root.id));
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