>on 17/11/00 3:20 pm, Adam Wishart at [EMAIL PROTECTED] wrote:
>
>--can anyone help me with Global Variables?????
Normally a variable used in a handler is good only to the end of the
handler. It does not keep its value once you leave the handler. This is
what is known as "scope". Once you leave the handler the variable becomes
"out of scope" and is effectively destroyed. The next time into the
handler you essentially start the process over.
Of course, there are many needs to keep variables alive across handlers,
for the length of the program, even across movies. Also there is a need to
retain a value from one handler visit to another. This is where global
variables come in.
Once you say you're going to use a variable in "global mode", so to speak,
it will be entered into the global name pool and will keep its value
persistent. Even if you leave the handler, it still keeps its value. If
you transfer to another movie (or a movie in a window) you can still get at
that value.
To declare that you want to use a variable in "global mode", you must
declare it as global before you go to use it in that scope. For instance:
on startMovie
global username
username ="Bob"
end
If username was a "regular" variable , it would have lost its value ("Bob")
after you hit the "end" statement. But because it was declared as global
it instead is entered into the global name pool and can be referenced
elsewhere in the system.
To get at the variable elsewhere, you must also declare the name as global
and then you can reference it. For instance:
on enterFrame
global username
alert "Hello "&username
end
Unlike regular programming languages, declaring here is not really
allocating space for it, but rather specifying which name pool you will be
working out of. Therefore you must do it before the first reference to it
in a handler.
One shortcut is to list globals at the top of the script, before any
handlers. Then, they're valid for the whole script member. Example:
---- Top of script window ----
global username
on startMovie
username ="Bob"
end
on enterFrame
alert "Hello "&username
end
---- End of script window ----
To remember what's global and what's not, many people like the convention
of putting a little 'g' in front of the name. This has no technical
significance, but it can be handy for you and others in reading the
program. In this example, username would therefore actually be declared
and used as gUsername. Again, it's only for your convenience. Lingo
doesn't care what you call it as long as you're consistent.
Two last points: You can display globals in the message window, which is
nice. For instance, having executed the above code, you could do in the
message window:
put username (or put gUsername, if you called it that)
-- "Bob"
You can also assign globals in the message window. Any variables you
create in the message window are by default global.
username ="Nancy"
There is also a message window command you can use, which is: showglobals
which dumps all globals to the message window.
Hope this helps.
- Tab
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