Can someone explain 'Using ..." and "MonoBehaviour" in C#

using has a number of uses in C#. There are two that go at the top of a file that you are asking about and a third that you don't use too often in Unity.

1. using _; imports namespace. Namespaces are a collection of classes ands other data types that are used to categorize the library. UnityEngine for example is a collection of all the classes related to Unity. System.Collections is all the classes in .Net related to holding groups of data such as hashtable and array list. It is required whenever you use a class in that namespace. For example if you want to write to files then you need "System.IO."

2. Another use is that you can use it to disambiguate between different classes or to shorten a lengthy type declaration. This functions similar to a macro that you can use it to replace text.

      using System;
         using UnityEngine;
        //This is a common use for this to.  Both UnityEngine and System have a class called object so you should specify which one "Object" refers to.
        using Object = UnityEngine.Object;
    
         //BE CAREFUL DOING THIS BECAUSE IT CAN MAKE YOUR CODE HARD TO READ
         // BUT IT IS OCCASIONALLY USEFUL.
         using MyDictionary = System.Collections.Generic.Dictionary<int, string>;
   
   

The : MonoBehaviour tells Unity what class your class is derived from. Inheritance is a fundamental part of object-oriented programming (OOP) because it gives you several special features. It let's objects share common functionality, and it allows you to treat descendants like the base class. This behavior is called polymorphism and the wiki page explains it fairly well. You don't need to explicitly declare classes in javascript, but that's a common practice in C#.

The using statement will allow you to "use" (duh) other classes in your code.

If you didn't declare Using UnityEngine you would have to write: UnityEngine.Debug.Log("Hello World");

It allows you to exclude typing the namespace all the time.

Same rules apply for the System namespace.

There are actually two different ways to use using in C#

This is the less used way, the using statement. http://msdn.microsoft.com/en-us/library/yh598w02(v=vs.80).aspx

The way I suspect that you are using it is the using directive: http://msdn.microsoft.com/en-us/library/sf0df423(v=vs.80).aspx

The monobehaviour is the class that your script inherits from. http://unity3d.com/support/documentation/ScriptReference/MonoBehaviour.html

You will not have seen that before if you had been using Javascript as all javascript scripts automatically inherit a monobehaviour.

I would suggest that yo read up on inheritance in object orientated programming if you are not sure. http://www.csharp-station.com/Tutorials/lesson08.aspx

Hey MonkeyAssassin8,

I have been using C# for a little while, but I am certainly not a guru... Anyway, you almost never have to change the line "using UnityEngine;"; all that does it tell the Mono Engine that you are going to be programming in Unitys C#. Then next line "using System.Collections;"... Well, I am not quite sure myself, but if I had to guess I would say it might be the style that you are going to write in... Also, it might contain various information about what Syntax you can you...

-Hope I Helped!

-Edit-

I looked it up on MSDN, and they give the following explanation "The System.Collections namespace contains interfaces and classes that define various collections of objects, such as lists, queues, bit arrays, hash tables and dictionaries."

-Edit 2-

Okay, let me try to explain again...

Line1: "using UnityEngine;" Basically, this tells MonoDevelop that you are using Unity's version of C#. Notice you can reference GameObjects and CharterControllers?

Line2: "using System.Collections;" As I understand it, this tells MonoDevelop that you will be programming using things like arrays, hash tables, and queues. There are other things you can put there, such as System.Collections.Concurrent, System.Collections.Generic, System.Collections.ObjectModel, and System.Collections.Specialized. If you are just starting out, I don't suggest you change it, as System.Collections is very similar to Unity's Java Script. Also, you don't need to add anything extra to your code if your using System.Collections.

Line3: "public class ClassName : MonoBehaviour {" The first part "public" tells the code that this script can be accessed by other scripts. The next part "class" is telling the script that the next line will be the title of your code. "ClassName" this can be changed to what ever you want, but make sure you change the script's name to the same thing. Now "MonoBehaviour"... this is the base class every script derives from.

More details about ...C# using statement

robert