B4J Question How to create an instance of a B4J Class with JavaObject

[LucianDesign]

I want to create an instance of a B4J Class with JavaObject. I'm using the InitializeNewInstance method to create a new instance, but the B4J class Initialize method is never called.

 Dim jo As JavaObject
' jo.InitializeContext 'This is not working in B4J
jo = jo.InitializeNewInstance("b4j.example.myclass",Null)
Log(jo) 'The Initialize method is not executed

To call the explicit "_initialize" method I need the BA object (is this the right approach?)
How to create an instance of a B4J Class with JavaObject?

 

[stevel05]

Why do you want to do this? It would be easier to Create the class normally then assign it to a JavaObject, although I am not sure why you would want to.

 

[LucianDesign]

Hello,
Yes I know that. But I have a specific use case where I need to create the Instance of a B4J class on the fly. This case is similar to how the AddHandler (method from the Server Class) works.

Example:

Public testS As Server
testS.Initialize("")
testS.AddHandler("", "MyClass", True) 'Here we pass the class name that will be instantiated

 

[Erel]

Unlike jServer library you only need to deal with a specific set of classes. Create a factory sub that receives the class name and returns a class object:

Sub CreateClass(Name As String) As Object
 Dim res As Object
 Select Name
  Case "MyClass1"
    Dim mc1 As MyClass1
    res = mc1
 Case "MyClass2"
   Dim mc2 As MyClass2
   res = mc2
 End Select
 Return res
End Sub

 

[LucianDesign]

Hello Erel,
Thanks for the example. The factory method works great if you already know a specific set of classes.
The problem is that I'm building a library, and I need to create an instance of a B4J class that is not bundled in the library. It is in the project.

So ... a method from the lib needs to create an instance of a B4J class from the project.

 

[Erel]

Raise an event with ba.raiseEvent and let the developer return the object instance from the event.

 

[LucianDesign]

Hello,
The library is written with b4j ... I don't know how to use ba.raiseEvent to get a b4j class instance.
My use case is similar to AddHandler (method from the Server Class).

In the lib I have:

Public Sub RegisterPage(PageName As String, ClassName As String)
    If Not(LWPages.IsInitialized) Then
        LWPages.Initialize
    End If
    Dim tmpObj As JavaObject
   tmpObj = tmpObj.InitializeNewInstance(Utils.GetPackageName & "." & ClassName.ToLowerCase, Null)
 Log(tmpObj) 'The object is not initialized
 LWPages.Put(PageName, tmpObj) 'We put the object in a Map
End Sub

In a project using the lib ("MyClass" is defined in the project)

    'In a project using the lib
    myapp.RegisterPage("mypage", "MyClass")

 

[stevel05]

Without knowing the full functionality, we could be going round in circles, but from you last post it would be possible to do something like:

DIm Class As MyClass
Class.Initialize
myapp.RegisterPage("myPage",Class)

Then in the lib:

Public Sub RegisterPage(PageName As String, Class As Object)
    If Not(LWPages.IsInitialized) Then
        LWPages.Initialize
    End If

LWPages.Put(PageName,Class)

 

[LucianDesign]

Hello,
Thanks stevel05! Yes! This is another option.
All I wanted is to encapsulate the object creation in the RegisterPage method, but I guess there is no other way.

Thank you all!

 

[jgmdavies]

@LucianDesign

I suspect it's possible but I haven't tried in B4J. In B4A I use some inline Java to do this sort of thing (for a unit testing approach), e.g.

       Class c = Class.forName("myClass");
       Object o = c.newInstance();

       Method method = GetMethod(o.getClass(), "_initialize");

       Object returnObj = method.invoke(o, processBA);

(where GetMethod is my own, using 'c.getDeclaredMethods()'.)

The B4A 'Initialize' sub is called and I can then use the object as a 'normal' B4A object, e.g. using 'CallSub' to call its other subs.

HTH,
Jim