Is 'e' a method, a property or what?

Duncan Lithgow

In a piece of code as below what is 'e'? I thought that in C# all variables have to be declared, so it isn't a variable. Is 'e' a member of the Element class ( a property) ? I don't understand what is is or how it knows what it is... I don't see it being declared ... have I missed the lesson about how to declare a new method?

foreach (Element e in new FilteredElementCollector(doc)
        .OfClass(typeof(FamilyInstance)).OfCategory(BuiltInCategory.OST_Doors))
{
         FamilyInstance fi = e as FamilyInstance;
         FamilySymbol fs = fi.Symbol;
         Family family = fs.Family;
         info += family.Name + ": " + fs.Name + ": " + fi.Name + Environment.NewLine;
}

I appreciate that this is a beginner question, but I don't know where to look to fully understand this code.

And how is fi being declared, what type is it, and how does it know what type it is?

(this code uses the Autodesk Revit API)

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes12y ago
Although Element is not a built-in type, Duncan, it's no doubt a type in the Autodesk Revit API as are FamilyInstance, FamilySymbol and several others which appear in this piece of code.

In C# any class, struct, interface, enum, delegate or array is a type and you can therefore declare variables of that type.

Consider for example this short little program. Here we've defined a class, MyType, and declared a variable 'mt' of that type:

using System;

class MyType
{
public void MyMethod()
{
Console.WriteLine("Hello from MyType");
}
}

class Program
{
static void Main()
{
MyType mt = new MyType();
mt.MyMethod();
Console.ReadKey();
}
}

The output is:

Hello from MyType

One of the most powerful features of any object oriented language is that you are not just limited to built-in types but can create an unlimited number of custom types to represent whatever concepts or 'real life' objects you're trying to model.
Duncan Lithgow12y ago
Hi Vulpes

Thanks for your answer. Thanks for the concept of control variables - useful term to remember.

I get that e is a variable, and when you say it is a variable of type Element that answers my confusion about the variables type not being declared. But 'Element' is not a type in C# - is it?

Variable types are
* string
* bool
* int
and so on.

How can Element be a type of variable?
Vulpes12y ago
Well 'e' is a variable of type Element.

It is in fact the 'control variable' of the foreach statement and it only exists within the context of that statement.

You can also do this with a for statement:

for(int i = 0; i < 10; i++)
{
Console.WriteLine(i);
}

Here, 'i' is the control variable of type int of the for statement. Once the for statement ends 'i' is no longer defined i.e. its scope only extends over the for statement.

Any clearer?