Dynamic variable change VB.NET

Question

I have this code in VB.NET:

Dim Hello As String = "123"
temp = Fix_this(hello)
 
Function Fix_this(The_content As String)
    The_content = "456" : Return "test"
End Function

I want function Fix_This to change the string variable "Hello" without knowing the name of that variable even. I know I can return a new Hello string but I want to return something else.

Is there a way in Fix_this function, it can figure out the source of the "The_content" ?

So my goal is fix_this function to find out the source of The_content is "Hello" and then being able to dynamically change the Hello value in the function. No idea if I'm making any sense?

So let's say I succeed and I get string value "Hello". How do I then change the hello value? For example:

Source_of_The_content =   "Hello"

If I do this:

Source_of_The_content  = "New"

it obviously is not going to change the "Hello" string value to New.

Étienne Laneville · Accepted Answer · 2022-04-28 22:09:41Z

2

If you want a Function or Sub to modify the parameter it receives, declare the parameter as ByRef. Using your Fix_thisfunction:

Function Fix_this(ByRef The_content As String) As String
    The_content = "456"
    Return "test"
End Function

If you run the following code, The_content will be "456":

Dim Hello As String = "123"
MsgBox("Hello before Fix_this: " & Hello)
Dim temp As String = Fix_this(Hello)
MsgBox("Hello after Fix_this: " & Hello)
MsgBox("temp: " & temp)

You can also do this by using a Sub if you are just interested in modifying The_content:

Sub Fix_this(ByRef The_content As String)
    The_content = "456"
End Sub

edited Apr 28, 2022 at 22:09

answered Apr 28, 2022 at 22:02

Étienne Laneville

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4 Comments

Maria Over a year ago

this is awesome and perfect. Just what I needed. One question though. How can I do this without using function? How can I change a variable without changing it directly by just knowing the name of the variable in vb.net? Thank you !!!!!

Étienne Laneville Over a year ago

Take a look at CallByName. You can create a property for your variable like Public Property hello As String = "123" and then update it like this: CallByName(Me, "hello", CallType.Let, "456")

John Over a year ago

@Maria, why do you think that you need modify a variable based on name stored as a string? It's very rare that you should need to do that so, if you think you do, it's probably the result of bad design.

Craig Over a year ago

@Maria If you want to be able to access values by name, you should set up the data structure for managing it yourself. For what you are discussing, I would recommend looking at a Dictionary(Of String, String).

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