Bug? Bug with Types

Scantech · May 14, 2019

See attach file. Click the button twice and observe the list size(lData).

first time = 1
second time = 0

Reinitializing the list(Starter.DTCView.lDataDTC.Initialize) in type causing this behavior. Its interfering with the other list(lData).

Scantech · May 14, 2019

I also notice passing lData to other list will cause lData to be empty on second attempt? That occurs if i initialize the list that gets the lData.

Scantech · May 15, 2019

Its actually an issue with List not Types.

B4X:

Sub Globals
    'These global variables will be redeclared each time the activity is created.
    'These variables can only be accessed from this module.

    Private Button1 As Button
    Dim lData As List
    Dim lstGet As List
End Sub

B4X:

Sub Activity_Create(FirstTime As Boolean)
    'Do not forget to load the layout file created with the visual designer. For example:
    Activity.LoadLayout("1")
 
    lData.Initialize
    lData.Add("HI")
 
End Sub

B4X:

Sub Button1_Click

    lstGet.Initialize
    lstGet = lData
    Log(lData.Size)

End Sub

*** Service (starter) Create ***
** Service (starter) Start **
** Activity (main) Create, isFirst = true **
** Activity (main) Resume **
1
0
** Activity (main) Pause, UserClosed = true **
** Service (starter) Destroy (ignored)**

Pendrush · May 15, 2019

When you click button fot the first time, you create reference between two lists

B4X:

lstGet = lData

Then you click button for the second time and in this line

B4X:

lstGet.Initialize

you Initialize already referenced list. This make both list just initialized without any data, size is 0.
This is normal behavior across B4X.

You can CopyObject with B4XSerializator, see this link

Erel · May 15, 2019

This is not a bug. It happens because of two reasons:
1. Both variables point to the same object.
2. The assumption that calling Initialize creates a new object is incorrect though it looks like this in many cases.

The correct way to create a new object is by calling Dim. In this case, as the list is part of a type, you should do it like this:

B4X:

Dim l As List
l.Initialize
Starter.DTCView.lDataDTC = l

Scantech · May 16, 2019

One more explanation, please.

This one

B4X:

Sub Globals
    'These global variables will be redeclared each time the activity is created.
    'These variables can only be accessed from this module.

    Private Button1 As Button
    Dim lstGet As List
    Dim lstSet As List
End Sub

Sub Activity_Create(FirstTime As Boolean)
    'Do not forget to load the layout file created with the visual designer. For example:
    Activity.LoadLayout("1")
    lstSet.Initialize

End Sub

B4X:

Sub Button1_Click
    lstSet.Clear
     lstSet.Add("HI")
    Data(lstSet)
End Sub

Sub Data(l As List)  
    lstGet.Initialize
    lstGet = l
    Log(l.Size)
End Sub

Same result 1 and then 0. l as list is local variable and gets created with new object?

Erel · May 16, 2019

Exactly the same.

This line causes lstSet and lstGet to point to the same list object:

B4X:

lstGet = l

When you later call lstGet.Initialize the list is cleared.

B4X:

Sub Data(l As List)  
    Dim lstGet As List 'create new instance
    lstGet.Initialize
    lstGet = l
    Log(l.Size)
End Sub

Bug? Bug with Types

Scantech

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Erel

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Bug? Bug with Types

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