B4J Question How correctly to destroy a class instance ?

[peacemaker]

HI, All

If a B4X class contains other B4X classes and the instances are created runtime - if they are views, usually they need to be:

• created: init\create\show each instance of sub-classes
• shown in an interface (and resized)
• updated in an interface (and resized)
• maybe moved by user
• and destroyed

When an object is not needed for user - he should be able to delete it.
If object id is stored in a variable - nullification of variable does not help.
.IsInitialized of each created instance is always = True.

Dim objs As List
...

Private Sub butRefresh_Click
    Editor.RemoveAllViews
    Init_Area
    For i = 0 To objs.Size - 1
        Dim obj As b4xVectEdit_component = objs.Get(i)
        obj = Null ' does not help
    Next
    Generate_Diagram
End Sub

Sub Generate_Diagram
    If b4xVectEdit_component1.IsInitialized = False Then
        objs.Add(b4xVectEdit_component1.Initialize(Me, "Unit1"))
        b4xVectEdit_component1.Name = "Unit1"
        b4xVectEdit_component1.DesignerCreateView(Editor, Null, Null)
    End If
    b4xVectEdit_component1.Base_Resize(500dip, 500dip)
  
    If b4xVectEdit_component2.IsInitialized = False Then
        objs.Add(b4xVectEdit_component2.Initialize(Me, "Unit2"))
        b4xVectEdit_component2.Name = "Unit2"
        b4xVectEdit_component2.DesignerCreateView(Editor, Null, Null)
    End If
    b4xVectEdit_component2.Base_Resize(100dip, 300dip)

    If b4xVectEdit_component3.IsInitialized = False Then
        objs.Add(b4xVectEdit_component3.Initialize(Me, "Unit3"))
        b4xVectEdit_component3.InternalView = True
        b4xVectEdit_component3.Name = "Unit3_internal"
        b4xVectEdit_component3.DesignerCreateView(b4xVectEdit_component1.mRect.mBase, Null, Null)
    End If
    b4xVectEdit_component3.Base_Resize(200dip, 220dip)
    b4xVectEdit_component3.mRoot.Left = 65dip
End Sub

How correctly in B4J to destroy such structure and free memory up for sure ? For re-creation again of a fresh set.

 

[Daestrum]

While a variable has a 'live' reference it will occupy memory and garbage collect will ignore it.

In your example code, the object has a reference stored in the list, so making another copy and setting to null will do nothing.

Original

    For i = 0 To objs.Size - 1
        Dim obj As b4xVectEdit_component = objs.Get(i)
        obj = Null ' does not help
    Next

Modified

    For i = objs.Size - 1 to 0 Step -1
        objs.RemoveAt(i) ' will remove the reference from list which in turn (assuming nothing else reference that object) will make the original object available to GC
    Next

It's a hard concept to understand, unike C where you have a destructor for objects/classes.

 

[peacemaker]

objs.RemoveAt(i)

Anyway b4xVectEdit_component1.IsInitialized = always True.
Is it real to create some destructor here ? To kill the object right now and make sure it.

 

[agraham]

As @Daestrum says above, there is no need to explicitly destroy class instances in Java. As long as you have no references to it stored anywhere then the Java Garbage Collector will take care of reclaiming its memory - that's what it is designed to do!

 

[peacemaker]

In my code

Sub Generate_Diagram
    If b4xVectEdit_component1.IsInitialized = False Then
        objs.Add(b4xVectEdit_component1.Initialize(Me, "Unit1"))
        b4xVectEdit_component1.Name = "Unit1"
        b4xVectEdit_component1.DesignerCreateView(Editor, Null, Null)
    End If
    b4xVectEdit_component1.Base_Resize(500dip, 500dip)

After first objects creation all components are with .IsInitialized = true.
Is it possible to make it again .IsInitialized = false ?

How to continue using the b4xVectEdit_component1 for another instance ?

upd.

Ahhh

Sub Generate_Diagram
    Private b4xVectEdit_component1, b4xVectEdit_component2, b4xVectEdit_component3 As b4xVectEdit_component
    
    If b4xVectEdit_component1.IsInitialized = False Then
        objs.Add(b4xVectEdit_component1.Initialize(Me, "Unit1"))
        b4xVectEdit_component1.Name = "Unit1"
        b4xVectEdit_component1.DesignerCreateView(Editor, Null, Null)
    End If
    b4xVectEdit_component1.Base_Resize(500dip, 500dip)

 

[Daestrum]

Not 100% sure what you are meaning, but If you have a class object that you need to reuse, just dim it again and it will be uninitialised. (just like when adding items to a table view - you create the item inside the loop)

Dim a As Something
a.Initialize
log(a.isInitialized) ' True
'do something with a
...
' now I want to reuse a
Dim a As Something
Log(a.isInitialized) ' False