B4J Question Set members of an instance via a Map with reflection?

[MathiasM]

Hello

I'm trying to find an easy solution for this:
I want to read a json file, and update an object accordingly. I made a small example of what I want to achieve. In my example I have a User class I want to alter:

Sub Class_Globals
    Private mFirstname As String
    Private mLastname As String
End Sub

Public Sub Initialize(Firstname As String, Lastname As String)
    mFirstname = Firstname
    mLastname = Lastname
End Sub

Public Sub getFirstname As String
    Return mFirstname
End Sub

Public Sub getLasttname As String
    Return mLastname
End Sub

Public Sub UpdateByMap(m As Map)
    Dim reflect As Reflector
    reflect.Target = Me
    For Each key As String In m.Keys
        reflect.SetField2("m" & key, m.Get(key))
    Next
End Sub

I'm calling this code this way:

Sub AppStart (Args() As String)
    Dim u As User
    
    u.Initialize("Tom", "Jones")
    
    Dim m As Map
    m.Initialize
    m.Put("Firstname", "Matt")
    
    u.UpdateByMap(m)
    
    Log(u.Firstname & " " & u.Lastname)
    StartMessageLoop
End Sub

Does anyone knows what is wrong here, It's the first time I use this reflection library: https://www.b4x.com/b4j/help/jreflection.html

The error is:

java.lang.NoClassDefFoundError: javafx/beans/value/ChangeListener

Thank you!

 

[agraham]

I don't know where to start with that Reflection code. It is so wrong that it is beyond comment. To use Reflection you need to understand the Java objects and their methods and you seem not to.

I don't see why you need to use Reflection at all. Cannot you just update the Map normally. You need to explain what you are trying to achieve.

P.S. I wrote the Reflection library

 

[MathiasM]

I don't know where to start with that Reflection code. It is so wrong that it is beyond comment. To use Reflection you need to understand the Java objects and their methods and you seem not to.

I'm sorry I butchered your library. I did look at the generated Java code, but it didn't point me to the right direction, as I miss some fundamentals to use this library I think.

I don't see why you need to use Reflection at all. Cannot you just update the Map normally. You need to explain what you are trying to achieve.

Well, I don't want to update a Map. I want to use a Map to update a User instance.

In the User class in my post above, the User has 2 fields. Firstname and Lastname.

What I actually want to do, is have a JSON file, something like this:

{
"Firstname": "Matt",
"Lastname":"Jones"
}

Then I want to load this JSON to a Map. In this Map the keys will be the field names of the User class, the values will be the values that I want to set on their respective field names.
That's why I wrote this code:

Public Sub UpdateByMap(m As Map)
    Dim reflect As Reflector
    reflect.Target = Me '<- Set the reflector target to this user instance
    For Each key As String In m.Keys '<- For each key, AKA Firstname, Lastname
        reflect.SetField2("m" & key, m.Get(key)) '<- Set the field name m + key AKA mFirstname, mLastname to their respective values AKA Matt, Jones
    Next
End Sub

Is what I want to do, setting fields trough a variable field name (from a JSON, Map, Whatever) possible?

Basically, I want something like CallSub, but for setting Fields, not calling subs. I hope I somewhat explained clearly what I want to achieve.

P.S. I wrote the Reflection library

Very nice! Way above my league!

Thanks for your reply!

 

[agraham]

I'n sure you don't need reflection. If Erel doesn't ninja me I'll look at it tomorrow - it's wine and TV time here now

 

[Erel]

Must it be a json file? B4XSerializator can serialize custom types.

Your code will work if you change "m" with "_m".
However it might fail in debug mode and you will need to do more work for complex types.

 

[agraham]

If Erel doesn't ninja me

Duly ninja'ed

It is so wrong that it is beyond comment.

My apologies. I am getting old I totally misread that code and didn't properly grasp your intent - new spectacles (and a brain overhaul) needed I think