How to create a new object from within a method?

BlitzMax Forums/BlitzMax Beginners Area/How to create a new object from within a method?

Amon_old

(Posted 2005) [#1]

Strict

Incbin "ball.png"

Global ball_list:TList = CreateList()

Type ball

	Field x:Int,y:Int,s:Int
	Global ballcount = 0
	
	Method create()
	
		b:ball = New ball
		ListAddLast ball_list,b
		
		b.x = Rnd(10,630)
		b.y = Rnd(10,470)
		b.s = Rnd(3,8)
		ballcount :+1
					
	End Method
	
End Type


Graphics 640,480,16,0

Repeat

	Cls
	
	For b:ball = EachIn ball_list
		
		If b.ballcount < 100
				
		b.create
		
		EndIf
	
	Next 
	
	FlushMem;Flip
	
Until KeyHit(KEY_ESCPE)

The above code does not work. I have a method that creates a new ball. The problem is when I try to call the mothod from within a loop it throws an error. Can anyone help?

Just to say that I have been using BlitzMax now for quite some time but without trying any of the OOP stuff. This is my second attempt at OOP and its beyond me for now.

Amon_old

(Posted 2005) [#2]

This wont work will it? I think because I have to create an object of type ball first then call b.create. So maybe the way I have set it up is wrong.

Perturbatio

(Posted 2005) [#3]

Without testing, something like this might be more like what you want:

Strict

Incbin "ball.png"

Global ball_list:TList = CreateList()

Type ball

	Field x:Int,y:Int,s:Int
	Global ballcount = 0
	
	Method create()
	
		b:ball = New ball
		ListAddLast ball_list,b
		
		b.x = Rnd(10,630)
		b.y = Rnd(10,470)
		b.s = Rnd(3,8)
		ballcount :+1
		return b			
	End Method
	
End Type


Graphics 640,480,16,0

Repeat

	Cls
	
	For b:ball = EachIn ball_list
		
		If b.ballcount < 100
				
		b:ball = ball.create
		
		EndIf
	
	Next 
	
	FlushMem;Flip
	
Until KeyHit(KEY_ESCPE)

Beaker

(Posted 2005) [#4]

You need to use a Type Function (not a Method):

Strict

Incbin "ball.png"

Global ball_list:TList = CreateList()

Type ball

	Field x:Int,y:Int,s:Int
	Global ballcount = 0
	
	Function create()
	
		Local b:ball = New ball
		ListAddLast ball_list,b
		
		b.x = Rnd(10,630)
		b.y = Rnd(10,470)
		b.s = Rnd(3,8)
		ballcount :+1
					
	End Function
	
End Type


Graphics 640,480,16,0

Repeat

	Cls
	
	For Local b:ball = EachIn ball_list
		If b.ballcount < 100
			b.create
		EndIf
	Next 
	
	FlushMem;Flip
	
Until KeyHit(KEY_ESCAPE)

There were other problems with undeclared variables and a misspelled key const.

FlameDuck

(Posted 2005) [#5]

What Beaker said. You can only invoke methods on pre-existing objects. There is however nothing to pprevent you from creating objects in a method - provided you have your creational responsabilities sorted out.

For example: A Ball should not be able to spawn additional balls, however it is perfectly reasonable that the balls' collector object (TList here) spawns additional balls.