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Inter-behavior Communication

Global variables are one way scripts can share data and communicate with each other. Another form of communication can be the sending of messages with arguments to behaviors using the sendSprite, sendAllSprites and call commands.

The sendSprite command sends a message to all scripts attached to a specified sprite.
Syntax: sendSprite (whichSprite, #customMessage, arguments)

The sendAllSprites command sends a message to all scripts attached to all sprites.
Syntax: sendAllSprites (#customMessage, arguments)

With both of the above commands, if none of the sprites’ behaviors have a handler that corresponds to the message, the message will pass down the hierarchy to the cast member script, the frame script and then the movie script.

The call command sends a message to a specific behavior. Unlike the sendSprite and sendAllSprites commands, using call will not pass the message to cast member scripts, frame scripts or movie scripts.
Syntax: call (#customMessage, script, arguments)

The customMessage is replaced with the message and arguments is replaced by any values for parameters of the message to be sent. The symbol (#) operator must precede the message.

The call command is often used together with scriptInstanceList. The scriptInstanceList is a sprite property in the form of list of behaviors attached to a sprite. The property is available while the movie plays, when the movie is not running, the list is empty.
Syntax: sprite(whichSprite).scriptInstanceList

Example 1
The example below sends the custom message mChangeDirection with the argument of #left to all behaviors attached to sprite 1. You will see this behavior in context a little lower down in this technote.

on mouseUp me
  sendSprite (1, #mChangeDirection,#left)
end

We could have sent the custom message to a specific behavior instance. If we knew the message was included in behavior instance 1 of sprite 1, we could write the following:

on mouseUp me
  -- get the reference of first behavior of sprite 1
  -- i.e. the first item on the scriptInstanceList
  xref = getAt (sprite(1).scriptInstanceList, 1)
  -- run the mChangeDirection handler in the
  -- referenced script,with a parameter value of #left
  call (#mChangeDirection, xref, #left)
end

Example 2
on keyDown
  case the keyCode of
    121 : sendSprite (10, #mouseUp)
    116 : sendSprite (11, #mouseUp)
  end case
end

The above script checks if the pageUp or pageDown keys have been pressed by identifying each key's numerical value (the keycode). If the keycode is 121 (pageUp), the mouseUp event attached to sprite 10 is activated. If the keycode is 116 (pageDown), the mouseUp event attached to sprite 11 is activated. No arguments are sent with the message. This script could be used in a situation where you have a slide-show with forward and back buttons (sprites 10 and 11), and where pageDown is linked to the forward button and pageUp is linked to the back button.

Changing the parameter value in a behavior using sendSprite

Below is a simple automatic animate behavior. If you drag it onto a sprite, it will make a sprite move up or down, left or right depending on what its direction property (as defined by pMyDirection) has been set to.

-- define properties
property spriteNum, pMyDirection, pMyMoveDistance

-- event handlers
on beginSprite me
  pMyMoveDistance = 1
end

on exitFrame me
  mMove me, pMyDirection
  -- activates custom message mMove with 2 parameters
  -- me and pMyDirection
end

-- custom handlers to allow change of direction
-- (in separate behavior)
on mChangeDirection me, newDirection
  pMyDirection = newDirection
end

-- custom handlers to move sprite within this behavior
on mMove me, whichDirection
  case pMyDirection of
    #up:sprite(spriteNum).locV = \
sprite(spriteNum).locV - pMyMoveDistance
    #right:sprite(spriteNum).locH = \
sprite(spriteNum).locH + pMyMoveDistance
    #down:sprite(spriteNum).locV = \
sprite(spriteNum).locV + pMyMoveDistance
    #left:sprite(spriteNum).locH = \
sprite(spriteNum).locH - pMyMoveDistance
  end case
end

-- prompt user for parameter value
on getPropertyDescriptionList
  pList = [:]
  addProp pList, #pMyDirection, [#comment: \
"What direction should I move?", #format:#symbol, \
#default:#left, #range:#stationary, #left, #right, #up, #down]
  return pList
end

Note: The continuation symbol ( \ ) was used above to split a statement over 2 lines but still treat it as a single entity. This was done here because it would not fit into the width of this page layout.

We can create a button that sends a message to this behavior to change the direction. For example, the following will change the direction of the animated sprite to move left.

on mouseUp me
  sendSprite (1, #mChangeDirection,#left)
end

The above could have been written as:
on mouseUp me
  sendSprite (1, #mChangeDirection,me, #left)
end

But the me is not essential in this situation.