User Guide

Chapter 16396
Using handlers
As described in “Using messages to identify events” on page 394, Director sends messages to
handlers within scripts when specific events occur. You attach a set of handlers to an object by
attaching the handlers’ script to the object. See “Creating and attaching scripts with the
Script window” on page 412.
Each handler begins with the word
on followed by the message that the handler should respond
to. The last line of the handler is the word
end. You can repeat the handler’s name after end, but
this is optional.
When an object receives a message that corresponds to a handler attached to the object, Director
runs the Lingo statements within the handler. For example, the
mouseDown message indicates that
the user clicked the mouse button. To indicate in your script that an action should be performed
when the mouse is clicked, you include a line in your script that begins with
onMouseDown. You
follow this line with the Lingo statements that should execute when the script receives the
mouseDown message.
Using arguments to pass values to a handler
By using arguments for values, you can give the handler exactly the values that it needs to use at a
specific time, regardless of where or when you call the handler in the movie. Arguments can be
optional or required, depending on the situation.
To create arguments for a handler:
• Put the arguments after the handler name. Use commas to separate multiple arguments.
For example, the following handler, called
addThem, adds two values it receives in the arguments a
and
b, stores the result in local variable c, and uses the Lingo term return to send the result back
to the original handler:
on addThem a, b
-- a and b are argument placeholders
c = a + b
return c
end
When you call a handler, you must provide specific values for the arguments that the handler
uses. You can use any type of value, such as a number, a variable that has a value assigned, or a
string of characters. Values in the calling statement must be in the order they follow in the
handler’s arguments, and they must be surrounded by parentheses.
The following statement is a calling statement for the
on addThem handler:
set mySum = addThem(4, 8)
Because 4 is first in the list of arguments, Lingo substitutes it for a in the handler. Likewise,
because
8 is second in the list of arguments, Lingo substitutes 8 for b everywhere in the handler.
After the calling statement sends these parameters to the handler, the handler returns the value
12,
which corresponds to the variable
c inside the on addThem handler. The variable mySum in the
calling statement is then set to
12.
You can also use expressions as values. For example, the following statement substitutes
3+6 for a
and
8>2 (or 1, representing TRUE) for b, and would return 10:
set mySum = addThem(3+6, 8>2)