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thunderxlight11111
thunderxlight11111
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explain this to me please

Apr 17, 2012 1:18 PM

hi, how are guys

 

first thing i wanna say iam so sorry because iam so useless in this forum  , am just asking without helping 

 

 

here the problem i designed some games and i always get this error 1009 error i.ve read it in this  book (foundation game programming )  and i still cant understand what does he mean

 

here (iam asking in the blue lines and the   problem red lines

help me please it is realy confusing me in game programming)

Adding and removing objects from the stage

Before you look at the code of the game, I need to explain the new way in which classes are being initialized.

Dungeon Maze Adventure has been planned as a multilevel game. If you want to add another

level, it means that you have to remove dungeon one from the stage and add dungeon tow . This gets you

 

into a tricky technical situation regarding how AS3.0 initializes objects in the Flash Player when the

game runs. It’s an extremely important issue to be aware of because it will plague the development of

your Flash games and give you countless sleepless nights if you don’t understand why it happens and

how to solve it.

 

Let’s take a look a look at this problem. When the published SWF of the game runs, it does two things

(in this order):

1. It initializes all the objects by running the constructor methods in their classes.

2. It displays the objects on the stage. (It displays them one by one in the order in which they

were dragged to the stage from the Library when you designed the game in the FLA.)what does he mean by saying display them on the stage?? because i cant see them without addchild method and he said the swf file display them??!!!!!!!!

 

 

 

Here’s the issue: if the class’s constructor method includes a reference to the stage or an object that

is on the stage that hasn’t yet been displayed, you’ll get an error message saying this: here i cant understand any single word!!

Error #1009: Cannot access a property or method of a null object reference.

 

If you’re adding objects to the game, there’s a good chance that many of those objects have to access

the stage as soon as they’re created. They might need to do this to set stage boundaries or access the

properties of other objects that are also on the stage. If they can’t find the stage object because they

haven’t been added to the stage yet, AS3.0’s compiler will “throw its hands in the air” and you’ll see

the preceding error message.

To solve this problem, you need to initialize objects only when they they’ve been added to the stage,

not before.

 

done

 

 

i hope you guys can help me

thank you

729 Views   7 Replies   Latest reply: sinious, Apr 19, 2012 7:21 AM
 
Replies
  • _spoboyle
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    1. _spoboyle,
    Apr 18, 2012 1:42 AM   in reply to thunderxlight11111
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    2. It displays the objects on the stage. (It displays them one by one in the order in which they

    were dragged to the stage from the Library when you designed the game in the FLA.)what does he mean by saying display them on the stage?? because i cant see them without addchild method and he said the swf file display them??!!!!!!!!

     

    are you using pure AS3 or are you using the design tool in CS4/5

     

    when using the design tool in CS4/5 you can have objects in the library and drag them to the stage. this will automatically at the objects to the stage without having to call addChild()

     

    if you are using pure AS3 you don't have access to this and you have to explicity add all you objects using addChild

     

    Here’s the issue: if the class’s constructor method includes a reference to the stage or an object that

    is on the stage that hasn’t yet been displayed, you’ll get an error message saying this: here i cant understand any single word!!

    Error #1009: Cannot access a property or method of a null object reference.

     

    you would only need to add a reference to the stage for non DisplayObjects (e.g. generally things that aren't sprites or MovieClips)

    All DisplayObjects have access to the stage via the stage property. The stage property for an object is always null until you call addChild, not when they are constructed as you mention.

     

    if you are trying to use the stageWidth and stageHeight property you shouldn't do this in the constructor of the object instead you would need to add an Event.ADDED_TO_STAGE listener and then do any configuration based ont he stage within this listener.

     

    hope that clears it up a little

     
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  • thunderxlight11111
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    2. thunderxlight11111,
    Apr 18, 2012 2:07 AM   in reply to _spoboyle
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    am not sure

    here

    a reference to the stage or an object that

    is on the stage that hasn’t yet been displayed!!!

     

    how that can be on the stage and hasn.t yet been displayed?

     
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  • _spoboyle
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    3. _spoboyle,
    Apr 18, 2012 2:10 AM   in reply to thunderxlight11111
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    the only way this could happen is during the small time between adding a object to the stage and the displaylist being updated

     
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  • thunderxlight11111
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    4. thunderxlight11111,
    Apr 18, 2012 5:20 AM   in reply to _spoboyle
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    so why it initializes their objects before  displaying on the stage ??!! it still confusing me 

    i also did this

    i created small project with 2 classes 

    the first (class) has an instance in the stage and there is conditional 

    this

    public function g(event:MouseEvent):void

            {

               

                var class2instance:class2 = new class2instance  ;

                addChild(class2instanceb);

                removeChild(this);// the first class instance

            }

     

    and yeah when i did this thing its adding child but its not removing  

    i still cant totally get it

    you can ignore this msg  your answer was the correct anyway but i couldn.t get it all thank you

     
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  • sinious
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    5. sinious,
    Apr 18, 2012 7:02 AM   in reply to thunderxlight11111
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    Be careful what you name things. Don't use a variable name that is a class name.

     

    e.g.: rewrite that function:

     

    public function g(event:MouseEvent):void

    {

         var c2instance:class2 = new class2();

         MovieClip(parent).addChild(c2instance);

         removeChild(this);

    }

     

    In your previous method you were adding an instance (of what I assume) is class2 but you called it class2instance (I assumed this was a typo). You then ran a simple addChild() which would add it inside the current object the function is running from. Then you removeChild(this) which removes not only the current object but what you just tried to add to the displaylist.

     

    So I changed it up so you'd be adding class2 to the parent so it actually shows when you removeChild(this).

     
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  • thunderxlight11111
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    6. thunderxlight11111,
    Apr 19, 2012 1:38 AM   in reply to thunderxlight11111
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    yeah thank you alot that help me much , i always get errors because of theses stupid things

     

    thank you again brother

     
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  • sinious
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    7. sinious,
    Apr 19, 2012 7:21 AM   in reply to thunderxlight11111
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    Scope is a tough thing to grasp sometimes. Just imagine your display list and it will help you quite a bit.

     

    Good luck

     
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