state management : 

example code: stateMgt.dir

In more complex applications, objects in the system need to keep track of their internal state and behave differently depending on that state. For example, in a car, different things work depending on the position of the key:

• Key OFF: lights work, nothing else works
• Key AC: lights work, radio and other electrical works, engine off
• Key STARTER: starter motor turns
• Key RUNNING: engine runs, everything works

In software, taking care of these different states and corresponding behaviors is called "STATE MANGEMENT". It simply means that the software:

• keeps track of the current state
• behaves according to this state
• and (often) manages the trasitions from one state to the next
  

In this simple example, the sprite upper sprite object pays attention to where it is in the horizontal (.locH) dimension, and shows a different word and plays a different sound depending if it is in the left, middle or right hand side when the user clicks on it.

function mouseDown() {
  xPos = sprite(this.spriteNum).locH;
  theSprite = sprite("textMessage");
  
  if (xPos < 200) { 
    // left side
    //
    theSprite.member = member("more");
    sound(1).play(member("seagulls"));
  } else if (xPos >= 200 && xPos < 400) {
    // middle
    //
    theSprite.member = member("thanks");
    sound(1).play(member("bark"));
  } else if (xPos >= 400) {
    // right side
    //
    theSprite.member = member("ouch");
    sound(1).play(member("mosquito"));
  }     
}

function mouseUp () {
   theSprite = sprite("textMessage");
   theSprite.member = member("hello");
}

function mouseLeave () {
   theSprite = sprite("textMessage");
   theSprite.member = member("hello");
}
         

function enterFrame () {
   thisSprite = sprite(this.spriteNum);
   thisSprite.locH += 2;
   if (thisSprite.locH > 600) thisSprite.locH = 0;
} 

In this example, the state is managed within the sprite rather than by the sprite's position on the screen. Each time the user clicks, the sprite shows a word and plays a sound corresponding to its current state. It also advances itself to the next state with a user click. So each click causes the sprite to change from one state to the next.

currentState = 1;
member("currentState").text = currentState.toString();

function mouseDown() {
             
   theSprite = sprite("textMessage");
   
   if (currentState == 1) { 
     // left side
     //
     theSprite.member = member("more");
     sound(1).play(member("seagulls"));
   } else if (currentState == 2) {
     // middle
     //
     theSprite.member = member("thanks");
     sound(1).play(member("bark"));
   } else if (currentState == 3) {
     // right side
     //
     theSprite.member = member("ouch");
     sound(1).play(member("mosquito"));
   } 
   currentState++
   if (currentState > 3) currentState = 1;
}

function mouseUp () {
   theSprite = sprite("textMessage");
   theSprite.member = member("hello");
   member("currentState").text = currentState.toString();
}

function mouseLeave () {
   theSprite = sprite("textMessage");
   theSprite.member = member("hello");
   member("currentState").text = currentState.toString();
}
         

function enterFrame () {
   thisSprite = sprite(this.spriteNum);
   thisSprite.locH += 2;
   if (thisSprite.locH > 600) thisSprite.locH = 0;
} 

all materials on this web site © copyright 2004, Philip van Allen