Why is this not working?

BlitzMax Forums/BlitzMax Beginners Area/Why is this not working?

altitudems

(Posted 2005) [#1]

When building the code below, I keep getting an error saying:

Compile Error
Unable to create new object of abstract "Type"

With no debugger, I'm clueless as to what I'm doing wrong. I am new to all this OOP stuff, but from what I've learned so far my code should be fine. Could someone enlighten me? :)

'CREATE GLOBAL LIST FOR SPRITE 
Global SpriteList:TList = CreateList()

'OBJECT:
'--- A simpler way to work with Images
Type tSprite
'--- SPRITE PROPERTIES ---
	Field Image:TImage
	Field Mode:Int
	Field ScaleX:Float
	Field ScaleY:Float
	Field Angle:Float
	Field Alpha:Float
	Field Tint:Int [3]
'-------------------------
	
'--- SPRITE CONSTRUCTOR ---
	Function Create:tSprite (_Image:TImage, _Mode:Int = SOLIDBLEND)
	'--- CREATE NEW SPRITE 
		Local o:tSprite = New tSprite
		'--- INITIATE SPRITE WITH DEFAULTS
			o.Image	= _Image
			o.Mode	= _Mode
			o.ScaleX	= 1.0
			o.ScaleY	= 1.0
			o.Angle	= 0.0
			o.Alpha	= 1.0
			o.Tint	= [255,255,255]
	'--- ADD NEW SPRITE TO LIST
		SpriteList.AddLast(o)
	'--- RETURN CREATED OBJECT 
		Return o
	End Function
'--------------------------

'--- RENDER METHOD ---
	Method Render (_X:Float, _Y:Float, _Frame:Int = -1)
	'--- CREATE TEMPORARY VARIABLES
		Local _ScaleX:Float
		Local _ScaleY:Float
		Local _Angle:Float
		Local _Alpha:Float
		Local _Mode:Int
		Local _Tint:Int [3]
		
	'--- STORE CURRENT SETTINGS
		_Angle		= GetRotation ()
		_Alpha		= GetAlpha ()
		_Mode		= GetBlend ()
		GetScale 		_ScaleX,_ScaleY
		GetColor 		_Tint[0],_Tint[1],_Tint[2]
		
	'--- SET OBJECTS SETTINGS	
		SetScale		ScaleX, ScaleY 		
		SetRotation	Angle
		SetAlpha		Alpha
		SetBlend		Mode
		SetColor		Tint[0], Tint[1], Tint[2]
		
	'--- SET FRAME
		If _Frame = -1 Then _Frame = Frame
		
	'--- DRAW IMAGE
		DrawImage		Image, _X, _Y, _Frame
		
	'--- RESTORE SETTINGS
		SetScale		_ScaleX, _ScaleY 		
		SetRotation	_Angle
		SetAlpha		_Alpha
		SetBlend		_Mode
		SetColor		Tint[0], Tint[1], Tint[2]
	End Method 		
'-----------------------
	
	Method Update() Abstract

End Type

Bot Builder

(Posted 2005) [#2]

Ah. You have an abstract method in there which makes it an abstract type. You can't create a sprite as you are trying to do in the create function because you can't create an abstract type.

altitudems

(Posted 2005) [#3]

Thanks for your reply.
Are you sure that's the problem?

If I completely take out the abstract method, it still does not compile.

Warren

(Posted 2005) [#4]

Right, abstract is saying that you want other types to derive from this one and that those derived types MUST implement your abstract functions. You can't instantiate any class that has a missing or declared abstract method.

And FYI, a debugger wouldn't be of any use here as this is a compile error...

Bot Builder

(Posted 2005) [#5]

Why would ou want anything to derive from sprite anyway? You should just make the update method a normal method. Also, when something "does not compile" It's handy to post the error message, and prefereably the line number, local to the top of the code snippet

altitudems

(Posted 2005) [#6]

@ WarrenM
Thanks for the clarification, I think I get abstract methods better now. But even without any abstract reference I still get a "compile error" :)

[edit] Actually you guys are right it was that I was abstracting tSprite. Still I wonder why your not allowed to create an instance of an abstract class.

@ Bot Builder
Your right I should have posted what line number the error pointed to. I did however post the error message. But to save anyone the time of reading previous posts the error and location are:

LINE 23< CHAR 3:
      "Local o:tSprite = New tSprite"
Compile Error
Unable to create new object of abstract "Type"

As for the reason why I wanted to use tSprite as a base class; I wanted to create a tAnimatedSprite class that derived from the tSprite class.

Am I going about this all wrong? Should static and animated sprites be in the same class?

Thanks for your help guys!

Bot Builder

(Posted 2005) [#7]

You can't create an abstract class because if its abstract, then that means that some of its elements are undefined. That's the point of an absract class. Some elements are udefined so you define them later in an inheriting class. If the class is not abstract you can still override the definition of a method in a child class, and create a child or base class.