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Types n stuff

BlitzMax Forums/BlitzMax Programming/Types n stuff

Raz(Posted 2006) [#1]
I have a type "Tiles" and two sub types that extend it called "background" and "foreground"
Type Tiles
	Field X,Y
	Method Draw()
	
	End Method
End Type
Global Tile_List:TList = CreateList()

the sub types have their own draw methods
' Back
Type B_Type Extends Tiles
	Field F
	
	Method Draw()
		If x > Screen_X - Screen_Border And x < Screen_X_Max + Screen_Border
			If y > Screen_Y - Screen_Border And y < Screen_Y_Max + Screen_Border	
				DrawImage gfxTileset,x,y,f
			EndIf
		EndIf
	End Method
	
End Type

and when I create one of either sub types they get added to the main list 
Tile_List.AddLast( NewB )

I want to be able to easily draw all of the tiles with one command... so I was thinking
	For Local Tile:Tiles = EachIn Tile_List
		Tile.Draw()
	Next

However, this just runs the Draw method from the Tiles type. If I remove said method, the command "Tile.Draw()" doesnt work. But I want each entry in the list to run its own Draw method.

What am i doing wrong? ta!


H&K(Posted 2006) [#2]
Althouth the list excepts both subtypes, because they are tiles. The draw that you have overriddien in b_Type wont be called. Because the list is a list of tiles. Not B Types


Raz(Posted 2006) [#3]
Ahh got ya... so basically, I may as well just have two completely separate types, ya?


H&K(Posted 2006) [#4]
No, I think its doable with just one list, I think you put a field in ttile, that lets you know what each is. And casting always gets me, So maybe you can cast the B_Type back. Chris. I really dont know. Im not very good at this.

Wait till one of the 'sperts answer ;)


Raz(Posted 2006) [#5]
hehe ok, thanks for ya time anyway :)

Its something I will definately need for other objects in the game but it would be cool to get it working on simple terms first.

So anyone else got any ideas? ta!


Raz(Posted 2006) [#6]
Damnit, erm.... sorry.

Ive found the problem and as I suspected very early on but at the same time couldnt work out why..... the reason it didnt work was because I am a complete arse.

The "theory" I was going for does actually work perfectly though, which rocks :D


H&K(Posted 2006) [#7]
Well post the code then. And put me out of me missery


Brucey(Posted 2006) [#8]
The above code should indeed work.

Defining the list iterator as a super type will allow it to loop thru all instances of the super type *and* all its sub-types.
(Tiles being a super-type, B_Type being a sub-type)


Annoying, isn't it, when you *know* something should work in a particular way, and it doesn't... and always the last thing that dawns on you is that you may have coded it wrong somewhere along the line ;-)


Raz(Posted 2006) [#9]
thats the thing H&K the code I posted was actually spot on, it was some other part that I borked.

Note to self, use Strict. ;)

Ill give that super thing a look too ta Brucey. Currently I am just adding a newly create object to two (or more) lists.

This Extend stuff is really impressing me though, makes it so easy to define which objects i want to draw and which I dont.


assari(Posted 2006) [#10]
H&K, go through my tutorials here. The concepts are explained there
good luck


kfprimm(Posted 2006) [#11]
Method Draw() Abstract

that will fix it


H&K(Posted 2006) [#12]
Assari,

Ive looked thought all you tutorials, and whilst they are undoubtably good, they fail me utterly in one key feature. They are not memorable.

I dont mean offence by this, as Im only able to use MaxGui at all because of them. But they just dont seem to sync with me.


John J.(Posted 2006) [#13]
Maybe this tutorial will help:
http://www.blitzbasic.com/Community/posts.php?topic=59233

It describes inheritance and polymorphism and how they are best used in situations like this.