Addenda to Lingo in a Nutshell Chapter 12 - Beahviors and Parent Scripts

Chapter 12 - Behavior and Parent Scripts

Lingo in a Nutshell

A reader asks:

On page 137 of Director in a Nutshell, you show that setting "property spriteNum" at the beginning of a behaviour will allow you to use "spriteNum" in place of "the spriteNum of me". Is this unique to the spriteNum property or can one do this with other properties?

Bruce replies:

The spriteNum is a unique property of me. It is automatically assigned a value when the Behavior is instantiated. However, you can simulate a similar thing with any property by declaring it as a property variable and setting an initial value for the custom property in the beginSprite handler. (The following example uses D7's dot syntax.) In almost all my Behaviors, I create a custom property pSpr that I then use throughout other handlers, such as:

property pSpr, pOrig, pHigh, spriteNum



on beginSprite me

  pSpr  = sprite(spriteNum)

  pOrig = pSpr.member

  pHigh = member(pSpr.memberNum + 1)

end



on mouseEnter me

  pSpr.member = pHigh

end



on mouseLeave me

  pSpr.member = pOrig

end

Note that using pSpr is also faster than using sprite(spriteNum) repeatedly, because Director doesn't need to repeatedly create a sprite object. This is described in my article on dot syntax. Also note that you can NOT use pOrig in place of pSpr.member. to change the member of sprite. The following will simply set pOrig to the value of pHigh.

on mouseEnter me

  pOrig = pHigh

end

In most cases, I only need spriteNum once in my Behavior, so in practice I rarely declare spriteNum as a property and instead use me.spriteNum (which is much shorter than the verbose the spriteNum of me in D6). I'll skip declaring property spriteNum and write the above beginSprite handler as:

property pSpr, pOrig, pHigh



on beginSprite me

  -- Note, I use me.spriteNum instead of spriteNum

  pSpr  = sprite(me.spriteNum)

  pOrig = pSpr.member

  pHigh = member(pSpr.memberNum + 1)

end