Android Question can i set/change a variable when i pass it as parameter ?

Addo · Jul 11, 2020

i am trying to create a sub in another Module to set some local variables in a parameter

as example

B4X:

dim var as string

setvarstring(var)

log(var) 'This should be = something  can i do that ?


sub setvarstring(avar as string)

avar = "something"

end sub

LucasHeer · Jul 11, 2020

Basic4android follows Java parameter passing. Objects are passed by reference and "primitives" are passed by value.
Arrays are objects so are always passed by reference.

ByVal vs ByRef

Maybe I something in the documentation, Ive noticed in my applications that that when I call a Sub routine the "variables" that are passed are a reference to the variable. WHich is the default for VB6 as well. My question is, how to I pass a copy of the variable? The ByVal would achive this...

www.b4x.com

Since 'avar' is a string, it's being passed as a value. If you want to change the value of that specific variable, you'll have to reference it through it's module.

OR

return the value and change it from the original module:

B4X:

Dim var As String

var = setvarstring(var)

Log(var) 'This should be = something  can i do that ?


Sub setvarstring(avar As String)

    Return "something"

End Sub

Addo · Jul 11, 2020

then i should return it as string ? i cant set it directly without using return ?

LucasHeer · Jul 11, 2020

PassionDEV said:
then i should return it as string ? i cant set it directly without using return ?

You can reference the other module like:

B4X:

Sub setvarstring(avar As String)

    othermodule.var = "something"

End Sub

The problem is that it's passing your string as a value instead of a reference. Look at ByRef vs ByVal

Brian Dean · Jul 11, 2020

i am trying to create a sub in another Module ...

You cannot do this in the way you illustrate, as I think that you understand (arguments are passed by value). But there are alternative ways to get values into one module from another - global variables are the obvious one, but using a class object with properties (which are in fact subroutines in another module) is often a better scheme.

Erel · Jul 12, 2020

PassionDEV said:
i am trying to create a sub in another Module to set some local variables in a parameter

Declare a custom type with all the fields and pass it, or better create a sub that creates one and returns it.

In some esoteric cases where it does make sense to pass variables by reference then you can use arrays:

B4X:

Dim str(1) As String
SomeSub(str)

Sub SomeSub(str() As String)
 str(0) = "aaa"
End Sub

Android Question can i set/change a variable when i pass it as parameter ?

Addo

Well-Known Member

LucasHeer

Active Member

ByVal vs ByRef

Addo

Well-Known Member

LucasHeer

Active Member

Brian Dean

Well-Known Member

Erel

B4X founder

Similar Threads

Android Question can i set/change a variable when i pass it as parameter ?

Addo

Well-Known Member

LucasHeer

Active Member

ByVal vs ByRef

Addo

Well-Known Member

LucasHeer

Active Member

Brian Dean

Well-Known Member

Erel

B4X founder

Similar Threads

Privacy & Transparency

Privacy & Transparency