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class (Read 566 times)
Ynk
class
Nov 19th, 2009, 9:26am  
Hi,

I'm beginning in processing, and I need to do a basic slider
(those of libraries like ControlP5 are too complicated for me at the moment, and I would to modify styles)

So I started to make one, and I have already problems...

It say me that there is an NullPointer exception

There my code :

Code:

Slider slider1;

void setup(){
  /////////////////////////////////////
  size (500,500);
  background(120);
  /////////////////////////////////////

  Slider slider1 = new Slider(20,20,100,20);
}

void draw(){
  slider1.dessiner();
}

class Slider{
  int sPosX, sPosY;
  int sLargeur, sHauteur;
  //int sMin, sMax;
  //int sInitial;
  //int nom;
  //int valeur;

  Slider(int isPosX, int isPosY, int isLargeur, int isHauteur){
    sPosX = isPosX;
    sPosY = isPosY;
    sLargeur = isLargeur;
    sHauteur = isHauteur;
  }

  void dessiner(){
    noStroke();
    fill(150);
    rect(sPosX,sPosY,sLargeur,sHauteur);
    fill(80);
    rect(sPosX,sPosY,sLargeur,sHauteur);
  }

  /*void bouger(){
   if(mousePressed){
   rect(sPosX,sPosY,mouseX-sPosX,sHauteur);
   }
   }*/
}



if someone can have a look, thank you !
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blindfish
Re: class
Reply #1 - Nov 19th, 2009, 9:36am  
The problem is in setup.  You globally declare your Slider before setup (as you should) so you don't need to declare a new Slider object when you create/instantiate it.  So do this:

Code:
Slider slider1;

void setup(){
  /////////////////////////////////////
  size (500,500);
  background(120);
  /////////////////////////////////////
  // 'Slider' should NOT be declared here!
  slider1 = new Slider(20,20,100,20);
}


...Otherwise by declaring the Slider again in setup you create a local variable called 'slider1', which exists only inside setup(), and the global 'slider1' never gets created, hence the NullPointerException...

P.S.: You should also move your background(120) call from setup to draw() Wink
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Where is the what if the what is in why?
 
Ynk
Re: class
Reply #2 - Nov 19th, 2009, 9:46am  
thanks a lot !
I think it will not my last question, but it permise me to continue

thank you
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