Android Question (B4X) is it possible to get names and types of a custom type?

LucaMs · Jun 2, 2020

Is it possible to get names and types of a custom type?

B4X:

Type tPerson(Name As String, Surname As String, Age As Int)


' Something like:

'... GetTypeNumOfFields(tPerson)

'... GetTypeFieldName(tPerson, 0) ' <--- 0 = index of first field
'... GetTypeFieldType(tPerson, 0) ' <--- 0 = index of first field

Please, answer: "Yes, ..." ?

LucaMs · Jun 2, 2020

Searching, I "found" that Java does not have "Structures" - like C#-VB Net Struct-Structure "types".

So I suppose the B4X "custom type" is something specially created by Anywhere Software and maybe it's possible that it could expose what I asked for (adding this rarely used feature, I'm afraid).

LucaMs · Jun 2, 2020

Why am I wasting time on these strange things? I have a billion more urgent and important things to do!

Erel · Jun 2, 2020

There is no simple or very good way to do it. You can use reflection with some work to do it.

agraham · Jun 2, 2020

It's pretty trivial. I've tested this with jReflection in B4J but it should work in BA (touch wood!)

B4X:

    Dim tp As tPerson
    tp.Initialize
 
    Dim o1, o2 As Reflector
    Dim oa(0) As Object
    Dim str As String = ""
   
    o1.Target = tp
    o2.Target = o1.RunMethod("getClass")
    oa = o2.RunMethod("getFields")
   
    For i = 0 To oa.Length - 1
        Dim str1 As String = oa(i)
        Dim idx As Int = str1.LastIndexOf(".")      
        str = str & str1.SubString(idx+1) & ", "
    Next
    fx.Msgbox(MainForm, str, "")

A bit more code would give the type for each field if you wanted it.

LucaMs · Jun 2, 2020

Great, @agraham, thank you

LucaMs · Jun 2, 2020

I was afraid of having to use B4(A) internal objects, such as the BA that I have often seen.

LucaMs · Jun 2, 2020

Just to say what absurd idea I would have in mind, what I would like to be able to "create":
simulate the typed lists of other languages (VB Net, C#).

Of course, if Anywhere Software wanted to do it... it would be much better ?

LucaMs · Jun 2, 2020

Is this function enough/correct to check if an object is of a custom type declared in the Main module?

B4X:

Public Sub IsCustomTypeInMain(ObjectToCheck As Object) As Boolean
    Dim Refl1, Refl2 As Reflector
    Dim Objects(0) As Object
    Refl1.Target = ObjectToCheck
    Refl2.Target = Refl1.RunMethod("getClass")
    Objects = Refl2.RunMethod("getFields")
    Dim str As String = Objects(0)
    Return (str.StartsWith("public boolean b4j.example.main$_"))
End Sub

Um... maybe but only in b4j.
P.S. ... and only if the package name was "b4j.example"!

LucaMs · Jun 2, 2020

B4X:

Public Sub IsCustomTypeInMain(ObjectToCheck As Object) As Boolean
    Dim joBA As JavaObject
    joBA.InitializeStatic("anywheresoftware.b4a.BA")
    Dim PackageName As String = joBA.GetField("packageName")
    
    Dim Refl1, Refl2 As Reflector
    Dim Objects(0) As Object
    Refl1.Target = ObjectToCheck
    Refl2.Target = Refl1.RunMethod("getClass")
    Objects = Refl2.RunMethod("getFields")
    Dim str As String = Objects(0)
    Return (str.StartsWith($"public boolean ${PackageName}.main$_"$))
End Sub

???

agraham · Jun 2, 2020

Probably not. That will not be a unique class prefix.

Objects(0) in your example will be the IsInitialized Boolean field so you would be better checking for that explicit name and type but it might also occur in other objects.

If you are looking only to identify custom types from your application then why not just add a 'CustomType' field to the type declaration. You don't need to assign anything to it. You can then check for the presence of this field name.

B4X:

    Type tPerson(CustomType As Boolean, Name As String, Surname As String, Age As Int)

Or you could use a unique prefix to the type and check for that at the beginning of the class name.

B4X:

    Type MytypePerson(Name As String, Surname As String, Age As Int)

LucaMs · Jun 2, 2020

agraham said:
Objects(0) in your example will be the IsInitialized Boolean field so you would be better checking for that explicit name and type but it might also occur in other objects.

Object(0) (it is just an object of your useful routine to which I changed the name), will return:

B4X:

public boolean b4j.example.main$_tintarr.IsInitialized

for a custom type (test) I declared so in Main-Process_Globals:

B4X:

Type tIntArr(Numbers() As Int)

(to test what it would return if a custom type contained an array)

"t" is my "great" ? prefix for my custom types.

agraham · Jun 2, 2020

I'm afraid i am missing the point in this last post

LucaMs · Jun 2, 2020

This:

LucaMs said:
Dim str As String = Objects(0)

is your:

agraham said:
For i = 0 To oa.Length - 1
Dim str1 As String = oa(i)

Just oa(0)

and str1 will not be only an "IsInitialized" but:

"public boolean b4j.example.main$_tintarr.IsInitialized"

MicroDrie · Jun 2, 2020

LucaMs said:
Why am I wasting time on these strange things? I have a billion more urgent and important things to do!

You can only found the answer on that question .

Android Question (B4X) is it possible to get names and types of a custom type?

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