Popping an Alert – How it’s done

Yesterday I promised that we would talk a bit about how to put up dialogs from PDF forms

based on user action. Here, the key is to know a little bit about the App Object,

which is one of the objects Adobe defined, on top of core JavaScript, in Acrobat 4.0. Space

doesn’t permit an exhaustive discussion of the App Object here. The important thing for now

is to note that if you want to do dialogs at runtime, you’ll need to get familiar with App

Object methods.

The alert() method takes one mandatory argument (the string that you want the user

to see) plus up to two optional arguments. There is also a response() method for

two-way communication, which we’ll get to in a minute.

To call the alert method, you do something like:

i = app.alert('Are you sure you want overnight shipping? You live in 

Russia.', 2, 2);

This line of code, exactly as shown, will pop an alert showing the Are you sure…

text, with a warning icon and two response buttons, labelled Yes and No.

The first numeric argument specifies the kind of icon to show. There are four

possibilities:

0 = Error icon1 = Warning icon2 = Question icon3 = Status icon

These icons differ by operating system, as you might expect. On the Macintosh, the Zero

icon is a stop sign with a hand in it; icons 1 and 2 are the same as shown above; and icon 3

is the profile view of the little cartoon-guy face, an icon that’s been around since the

Lisa (circa 1983).

The second numeric argument gives you a change to specify the types of buttons you want

in your dialog. The default (zero) is an OK button and nothing else. The values 1, 2, and 3

correspond (in turn) to OK and Cancel, Yes and No, or Yes and No and Cancel.

You may have noticed that app.alert() returns a numeric value. This will be one of

the following:

0 = Error1 = OK2 = Cancel3 = No4 = Yes

In other words, if you specify a button group (see above), you can determine which type

of button the user pressed by examining the return value from app.alert(). Pretty handy.

It’s nice to be able to pop an alert when a user seems to be entering incorrect data, has

made a nonsensical choice, etc. But sometimes, an alert isn’t really enough. Sometimes you

need to be able to ask the user a specific question, and analyze (or maybe just stash) his

answer. We’ll talk about how to do that another time.

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