global variables

[Mark Lucas]

I have read all the books, and have searched for this information, but I have forgotten it if I saw it and hope someone can briefly answer this question about variables.

It looks like a global variable can be defined in the table structure, and in each form structure, and also in xbasic scripts, and action scripts. I am confused where exactly to define variables for different situations. I have experimented and eventually things work, but I'm generally not sure how I got it to work. For instance, a button on one form opens a second form, and then a button on that second form closes the second form and focus returns to the first form. Information is transferred from the first to the second form, then back to the first form. Where and how do I declare/define the global variable to do this. It seems I have to end up defining it in all places before this process works, but I'm sure that's not necessary.
Thanks, Mark

[forskare]

RE: global variables

Mark,

If I understand what you want to do, you're making it much more difficult than it needs to be.

"For instance, a button on one form opens a second form, and then a button on that second form closes the second form and focus returns to the first form."

This can easily be done with action scripting; perhaps you are?

"Information is transferred from the first to the second form, then back to the first form."

I'm confused. can you be msore explicit in your description on what info is transfered to the 2nd form? Does the same info go back to the 1st form? Or, is it info which you entered on form 2 that goes back to form 1? If the latter, why?

kenn

[Mark Lucas]

RE: global variables

Ken,
I have six fields, some of which may be empty. If one is empty, I want to manually enter a time of day (hh:mm) into the field, but I want to actually enter it on another form and include special directions, and have the user enter the hh in one field, and mm in another field, then combine them.

I did get this to work, but probably in a round about way. When clicking on a field, the second form is opened by a script in the OnArrive event. I need to tell the second form that it was opened from that particular field, so the time data that is entered in that second form will be placed back into the proper field on the first form. I gave a variable a value equal to the name of the field (to help keep everything straight).

By testing the value in the variable which is set to the name of each field, I can use conditional statements in the second form to place the data into the proper field on the first form. There is probably a more efficient way. I thought about using a variable in a statement such as topparent:variable.value=(calculated expression) where the variable represents the field in question, but could not get that to work. Can a variable be incorporated somehow into the syntax referring to the value property of a field? I am eager to learn the right way to do this.

Thanks for the help,
Mark

[JerryBrightbill]

RE: global variables

Mark

Essentially, global variables can be declared almost anywhere. The only requirement is that they be declared before they are used. If they are only used by a button action, they can be declared in the button code. If they may be used in many locations, then they can be declared at startup in an autoexec script. If they are needed for a table field rule for example, they can be declared in the table structure. The only difference is when the variable exists for the first time. After it is declared, it exists until it is deleted or the database closes.

Typically, I declare all globals on startup with a script that runs from an autoexec. The only exception is a global needed by a table for a field rule (which I use rarely). Then I also declare it in the table structure. This causes the global to be declared as soon as the table opens.

From the description of your process, variables may be a good way to transfer data. However, you may be able to uses shared variables instead of globals. These only exist until the current session is closed. Or, you could just use globals and delete them when the process is complete. In the end, the real question is - does it work? That is the main criteria.

Jerry

[forskare]

RE: global variables

Mark,

I vaguely understand what you're trying to do so I don't know if my next suggestion will work but is worth checking out.

Have a look at the lookupc function in the A5 Expressions Functions Reference book. I've used this successfully to copy data from a field in tbl_2 to like field in tbl_1. This is done in the tables field rules of tbl_1.

Another thought, are you sure you have the best set design for this?

Is it possible for you to zip the tables and sets (only those involved with the form) and attach them to your reply so we can take a look at it and get a better idea what you're trying to accomplish?

kenn

[martinwcole]

RE: global variables

declaring global variables more than once, which I often see done in scripts, was originally a bit confusing to me.

I thought to myself, well I declared the global variable in the autoexec script - oh my, what will happen if i declare it again? Will doing so destroy the data that is already in the variable? Why does this guy keep saying "dim global myvar as c" everywhere he goes?

In many languages, all scripts have to be "explicit" - that is, you cannot reference anything that was not declared in the script. So, as a matter of habit and style, many programmers continue to do so, although it is not necessary in Alpha. Since the languauge I came from did not require a global variable to be declared more than once, I never acquired the habit.

Once you declare a global variable, you can freely reference it anywhere, and its value remains until you change it. For example, I use "ans" as a global variable to get responses from a ui_message_box or ui_get_radio and use the value elsewhere, like in a report or query.

And in all applications, I use globels to pass values around, like cid-"customerid, ponum-"purchase order number, etc.