Hi Coder,
On the question of “if ... then” you are quite right- you don’t have to “close off” with “end if”. In the Rev menubar under “Help”, “Dictionary” I looked up “if” and there are four forms of the “if” control structure. If you want to execute just one statement in the “if”, e.g.
Code: Select all
on mouseUp
if field "Test" = 3 then beep 1
end mouseUp
... then, assuming you have a field “Test” and have typed “3” into it, pressing a button which contains the above script will produce a beep, as you expect. If you want several statements to be executed in the “if”, you can use:
Code: Select all
on mouseUp
if field "Test" = 3 then
beep 1
answer "Hello Coder!"
beep 1
end if
end mouseUp
... again, assuming a field “Test” you’ve typed “3” into, pressing the button will produce a beep, a message “Hello Coder!”, then when you press “OK”, another beep. So you use “end if” for multiple statements. I must admit I’ve always used the “end if” form as a matter of habit from using other languages, and also because of the ease of adding more statements into the conditional as a project develops. I’m glad you asked the question because it made me read the “if” section of the Rev dictionary again and realised I had an “end if” habit. It’s good to know the alternatives.
On the question about my use of variables and field names, perhaps the way I wrote the example was confusing. I had constructed my test script to be “self contained”- assuming you had a field whose name is “First” (i.e. field “First”) and a field whose name is “Second” (i.e. field “Second”) and a button with the script:
Code: Select all
on mouseUp
put "First" into testfield1
put "Second" into testfield2
put empty into field testfield2
if field testfield1 is not a number then
beep 1
answer "Please enter a number into the first field"
pass mouseUp
end if
if field testfield1 < 18 then
put 5 into field testfield2
end if
end mouseUp
... everything would work for you straight away. This makes the example work and uses your original variables testfield1 and testfield2, but we could do things more simply by writing:
Code: Select all
on mouseUp
put empty into field "Second"
if field "First" is not a number then
beep 1
answer "Please enter a number into the first field"
pass mouseUp
end if
if field "First" < 18 then
put 5 into field "Second"
end if
end mouseUp
... so you are quite right that in my original example I seemed to do something unnecessary- putting the word “First” into the variable testfield1 and the word “Second” into the variable testfield2. It’s important to be clear on what is a variable, like testfield1, and what it contains, like “First”. From you last post:
When you put the fields into variables..
Code: Select all
put "First" into testfield1
put "Second" into testfield2
I would do that like this:
Code: Select all
put field testfield1 into First
put field testfield2 into Second
There is an important difference between these statements:
... puts the word “First” into the variable testfield1. If we have a field “First” on our card, we can now refer to it as field testfield1. An example of how we might use this in a button script:
Code: Select all
global testfield1, testfield2
on mouseEnter
put "First" into testfield1
put "Second" into testfield2
end mouseEnter
on mouseUp
put empty into field testfield2
if field testfield1 is not a number then
beep 1
answer "Please enter a number into the first field"
pass mouseUp
end if
if field testfield1 < 18 then
put 5 into field testfield2
end if
end mouseUp
... if we “load” the names of the fields into the variables testfield1 and testfield2, we can easily modify the script to refer to two different fields “Third” and “Fourth”, simply by changing the mouseEnter:
Code: Select all
on mouseEnter
put "Third" into testfield1
put "Fourth" into testfield2
end mouseEnter
... which can be very convenient.
On the other hand:
... means something quite different. This is an instruction for Rev to place whatever the user has typed into field testfield1 into the variable First. Actually, as written, this won't work, and at this point I have a confession to make- my choice of names “First”, “Second”, “Third”, “Fourth” is not a good idea and the reason is interesting. As names for objects like fields/buttons these words will work- but not as variables. That is, you can’t say:
...Rev’s script editor won’t compile it and for a very good reason. “First”, “second”, “third”... are keywords used to refer to particular objects, e.g. a button with the script:
Code: Select all
on mouseUp
go to the first card of this stack
end mouseUp
... will take you to the first card of the stack. An acceptable alternative would be:
Code: Select all
put field testfield1 into firstValue
put field testfield2 into secondValue
... firstValue and secondValue are variable names that will work perfectly well. When these instructions are executed, whatever the user has typed into field testfield1 will be placed in the variable firstValue and whatever the user has typed in field testfield2 will be placed in secondValue. You can then do things with these variables, e.g.
Code: Select all
on mouseUp
put field testfield1 into firstValue
put field testfield2 into secondValue
if firstValue < secondValue then
put firstValue * secondValue into field testfield3
beep 1
wait 1 second
beep 1
end if
end mouseUp
... this isn’t a very interesting example but it gives the idea. Notice that because we are multiplying firstValue by secondValue we need both to be numbers- if the user typed “George” into field testfield1 and “5” into field testfield2 they would get an error message when they pressed the button. “George” * 5 doesn’t make any sense. To recap:
Code: Select all
put "MyFirstField" into testfield1
... puts the word “MyFirstField” into the variable testfield1. If later in the script we refer to field testfield1, it will mean field “MyFirstField”. If we then said:
Code: Select all
put field testfield1 into firstValue
... the variable firstValue will now contain whatever is typed into field testfield1, which we have already said means field “MyFirstField”. testfield1 is a variable in which we store the name of the field, in this case “MyFirstField”. If you have on the card a field “MyFirstField” and a button with the following script:
Code: Select all
on mouseUp
put "MyFirstField" into testfield1
put field testfield1 into firstValue
answer firstValue
end mouseUp
... type something into field “MyFirstField” and press the button, Rev will display a message dialog that uses whatever you typed. Again, this is not very exciting but does illustrate the use of variables. I hope some of these examples help. Your questions are perfectly sensible, and there were aspects of what I wrote that were certainly confusing. Please keep firing as many questions to the forum as you need. I’ve found the folks on the forum incredibly helpful, and different people explain things in different ways which helps everyone. Indeed, after preparing this and returning to the forum, I see Craig is already on the case.
Regards,
Michael
