Problems to free an Object
lazarus / 61-Beginners

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krull · 2017-05-20 15:25

Hello,

I think this is the last time, I need help with this program. It
should become a vertical shoot 'em up.

The problem is that everytime if you take the 1UP('heart') or if it
leaves screen bounderies, you get an Error back. Here the procedures
for 'heart' and the Invocation of the Object.
Thank for your Help.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.EnemyControlTimer(Sender: TObject);begin  randomize;  if
Enemy1.FreeMe=true then  begin    if not (Assigned (heart1)) {and
(random(8)=8)} then    begin      heart1:=THeart.create();     
heart1.pHeart:=Enemy1.pEnemy1;    end;    Enemy1.destroy();   
Enemy1:=TEnemy1.create(1);  end;  if Enemy2.FreeMe=true then  begin  
if not (Assigned (heart1)) {and (random(8)=8)} then    begin     
heart1:=THeart.create();      heart1.pHeart:=Enemy2.pEnemy1;    end; 
 Enemy2.destroy();    Enemy2:=TEnemy1.create(2);  end;  if
Player1.FreeMe=true then  begin    Player1.destroy(); sleep (500);
halt(0)  end;  if Assigned(heart1) and Heart1.FreeMe=true then  begin 
  FreeAndNil(heart1);  end;end;                 
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i constructor
THeart.create();begin  heart:=TBGRABitmap.Create('thunderflash.png'); 
heartSpeed:= 8;  FreeME:=false;  heartPosTimer := TTimer.Create(nil); 
heartPosTimer.Interval := 25;  heartPosTimer.OnTimer :=
@heartPosTimerTimer;  heartPosTimer.Enabled := true;end; destructor
THeart.destroy();begin end; procedure
THeart.heartPaint(p:Point;pOld:Point);begin  Form1.Canvas.FillRect(pHe
artFormer.x,pHeartFormer.y,pHeartFormer.x+heart.Width,pHeartFormer.y+h
eart.Height); 
heart.draw(Form1.Canvas,pHeart.x,pheart.y,true);end; procedure
THeart.heartPosTimerTimer(Sender: TObject);label 2;begin  if
pHeart.y>=Form1.Height then  begin    FreeMe:=true;  GoTo 2;  end;  if
(Player1.pPlayer.x<pHeart.x) and
(pHeart.x<Player1.pPlayer.x+Player1.playerShip.Width) and
(Player1.pPlayer.y<pHeart.y) and
(pHeart.y<Player1.pPlayer.y+Player1.playerShip.Height) then  begin   
Player1.Health:=Player1.Health+1;    FreeMe:= true;    Goto 2;  end; 
pHeartFormer:=pHeart;  pHeart.y:=pHeart.y+heartSpeed; 
heartPaint(pHeart,pHeartFormer);  2:end;

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Handoko · 2017-05-20 16:03

Hello krull.

I really want to help you, but you can you please provide the
"complete" source code? I can't compile and run it, so I can't test
it. Using eye-inspection only is very hard. 

Copy all the necessary files (including the images) into a new folder,
zip them and send it to this forum (using the attachment feature).

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Thaddy · 2017-05-20 16:20

Yes. I think we need more code, because what you suggest (error when
leaving the screen...) is not in the code you gave us.
So it must be something else.

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krull · 2017-05-20 16:21

OK here the whole files!
puh 250 KB max. I shrink it extreme.

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krull · 2017-05-20 16:46

Ok many Thanks, but I found it.
I have to disable the heartPosTimer. For me this seem to work, even if
I don't know why.

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Eugene Loza · 2017-05-20 17:05

Hi, krull!
I really like that you're making a computer game! It's really fun!
I'll make you some code suggestions, if you don't mind.

1. Never call Enemy1.destroy(); explicitly. Always use
FreeAndNil(Enemy1) or Enemy1.Free.
2. "random( 8 )=8" will never happen, because Random( 8 ) provides
random numbers from 0 to 7. 8 is not included.
3. Don't forget to FreeAndNil(heartPosTimer) in THeart.destroy.

Disabling heartPosTimer works because heartPosTimer calls back to
THeart which may already be destroyed. Freeing heartPosTimer in
THeart.destroy should solve this issue correctly. However, I'm not
sure you're doing the right program "structure".
Maybe, you'd better make some global game-cycle which will draw all
the sprites on-screen once per frame, not based on timers or threads,
which are hard to debug.

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Handoko · 2017-05-20 17:30

Glad to know you have solved the issue.

I tested your code but I can't make it work. Some advices hope it can
be useful to you:

- When providing code created using Lazarus, you can ignore/delete the
lib folder. The files inside that folder will be created automatically
when user compile the code.

- To make your code cross platform (compilable on Linux) you should
avoid using Windows unit. I didn't notice anything inside your code
that 'strictly' requires Windows unit.

- Nothing wrong with using Goto statement but avoiding to use Goto
will make code easier to debug especially for issues related with
logic. Learn to avoid Goto is a good practice to improve your ability
to solve problem with more organized way.

- You should avoid using hardcoding, instead use constant. Put your
constant declarations near the top, you can easily to modify the code
in the future. I saw you use hardcoding for file names, you will
realize someday it is not good to do so.