Unreal Development Kit Game Programming with UnrealScript：Beginner's Guide

上QQ阅读APP看书，第一时间看更新

Time for action – All classes are created equally

What does this mean for us in practical terms? Let's take a look at our friend AwesomeActor to see if he can help demonstrate.

Write the following code in our AwesomeActor class:

class AwesomeActor extends Actor
    placeable;

var() int MyInt;

function PostBeginPlay()
{
    `log(self @ MyInt);
}

defaultproperties
{
    MyInt=4

    Begin Object Class=SpriteComponent Name=Sprite
        Sprite=Texture2D'EditorResources.S_NavP'
        HiddenGame=True
    End Object
    Components.Add(Sprite)
}

We'll use an editable MyInt variable to see class behavior.

Compile the class and open up the editor. Next to our existing AwesomeActor, place another one.
Save the map and run it from the editor, then close out the game and editor.
Now let's take a look at our Launch2.log file:
```
[0010.61] ScriptLog: AwesomeActor_0 4
[0010.61] ScriptLog: AwesomeActor_1 4
```
We can see that class instances are created with the class name and then a number added to the end. Remembering that in programming everything starts with 0, in our case we have AwesomeActor_0 and AwesomeActor_1. Since we haven't changed anything about them yet, both have the default value of MyInt, 4.
How do we know which one's which? A handy bar at the bottom of the editor can help us. Reopen the editor and click on one of the AwesomeActors to select it. At the bottom of the editor we can see that instance's name.
From our log we can see that each instance of AwesomeActor has been created in the same manner. Now let's change one of them. Double-click on one to open up its properties, and change MyInt to 23.

Save the map and run the game, then exit and take a look at Launch2.log.

[0007.76] ScriptLog: AwesomeActor_0 4
[0007.76] ScriptLog: AwesomeActor_1 23

What just happened?

We can see that even though both instances were created from the same class blueprint, we can change them after they have been created. This is an important principle of object-oriented programming. Having classes lets us quickly create objects of the same type without having to have a separate file or code for each instance we're going to use. An object is created from the class with all of that class' properties, and then we can change them after they have been created.