Android Question DIM, Private, Public

Roger Daley · Oct 7, 2015

Hi all,

Just for clarification is there an advantage to using Private or Public as apposed to Dim for declaring variables?

By default:
a variable declared by Dim in Sub Process Globals is available to all modules.
a variable declared by Dim in Sub Globals is available only to the module in which it is declared.

A variable declared by Private in Sub Process Globals is only available to the module in which it is declared.
QUESTION 1: Is there an advantage to declare a variable using Private in Sub Process Globals over declaring the same variable using Dim in Sub Globals?

QUESTION 2: Is there a protocol to determine when and where to use these three declaration terms?

Regards Roger

Erel · Oct 7, 2015

See this tutorial: https://www.b4x.com/android/forum/threads/variables-and-subs-visibility.18628/

Roger Daley said:
QUESTION 1: Is there an advantage to declare a variable using Private in Sub Process Globals over declaring the same variable using Dim in Sub Globals?

Global variables are tied to the activity life cycle. In most cases only views should be declared in Sub Global.

Roger Daley · Oct 7, 2015

Thanks for the reply Erel your answer makes things a bit clearer.

My concern is that I am missing something by only using Dim.

1. I can see no reason to use either Private or Public in Sub Globals
2. I can see no reason to use Public in Sub Process Globals
3. Can you give me a practical example that would drive the use of Private in Sub Process Globals

Regards Roger

DonManfred · Oct 7, 2015

3) AFAIK a process global variable cannot be private.
2) you dont need to. DIM is the same here as all process globals must be public/are public
1) variables marke as private in globals of main activity cannot be accessed from other activities. Public variables can.

PS: I hope i did not tell bullshit

Roger Daley · Oct 7, 2015

Thanks DonManfred,

3) Code from Klaus's Tape Calculator Note the last line.

B4X:

Sub Process_Globals
' Designer Scripts AutoScale formula
'    Delta = ((100%x + 100%y) / (320dip + 430dip) - 1)
'    Rate = 0.5 'value between 0 to 1.
'    Scale = 1 + Rate * Delta

    Public Rate As Double
    Rate = 0.3 'value between 0 to 1.
    Private cScaleX, cScaleY, cScaleDS As Double
End Sub

Regards Roger

Erel · Oct 7, 2015

Don't use Dim in any of the global subs. Use either public or private.

1. In Sub Globals (which is only available in Activity modules) you should only use private.
2. In other "global subs" (Process_Globals or Class_Globals) you should use private or public based on the requirements.
3. Most variables in process_globals should be private. That is unless you want to access them from a different module.

Remember that only views (and other activity objects) should be declared in Sub Globals.

klaus · Oct 7, 2015

Roger Daley said:

Thanks DonManfred,

3) Code from Klaus's Tape Calculator Note the last line.

B4X:

Sub Process_Globals
' Designer Scripts AutoScale formula
'    Delta = ((100%x + 100%y) / (320dip + 430dip) - 1)
'    Rate = 0.5 'value between 0 to 1.
'    Scale = 1 + Rate * Delta

    Public Rate As Double
    Rate = 0.3 'value between 0 to 1.
    Private cScaleX, cScaleY, cScaleDS As Double
End Sub

Regards Roger

The code you are refering to is in the Scale Code module.
These variables, Private cScaleX, cScaleY, cScaleDS As Double, are private to the Scale Code module accessible from any Sub in this module but no need to access them from any other module.

Roger Daley · Oct 7, 2015

Erel said:
Don't use Dim in any of the global subs. Use either public or private.

1. In Sub Globals (which is only available in Activity modules) you should only use private.
2. In other "global subs" (Process_Globals or Class_Globals) you should use private or public based on the requirements.
3. Most variables in process_globals should be private. That is unless you want to access them from a different module.

Remember that only views (and other activity objects) should be declared in Sub Globals.

Thanks Erel, That really nails it down.
Regards Roger

mterveen · Apr 8, 2016

what's the purpose of dim then in the current ide? legacy code?

ArminKH · Apr 8, 2016

mterveen said:
what's the purpose of dim then in the current ide? legacy code?

maybe to maintain similarity to Visual Basic

Erel · Apr 10, 2016

mterveen said:
what's the purpose of dim then in the current ide? legacy code?

Yes. Public / private scope modifiers were not available in the first versions of B4A.

Android Question DIM, Private, Public

Roger Daley

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Erel

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Roger Daley

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DonManfred

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Roger Daley

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Erel

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klaus

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Roger Daley

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mterveen

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ArminKH

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Erel

B4X founder

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