Android Question Simple question on Classes

[Gary Milne]

I'm writing my first class in B4A. It will basically create a list of all of the points touched. I call the Initialize method and it works as expected. I then call Add_XY and I get an error because the ListX is Null.

I'm sure it's simple but it's not obvious to me what I need to do for this to work.

Any pointers appreciated.

'Class module
Sub Class_Globals
    Public MaxX As Int
    Public MinX As Int
    Public MaxY As Int
    Public MinY As Int
    Public ListX As List
    Public ListY As List
   
End Sub

'Initializes the object. You can add parameters to this method if needed.
Public Sub Initialize (X As Int, Y As Int)
    MinX = X
    MaxX = X
    MinY = Y
    MaxY = Y
   
    ListX.Initialize
    ListY.Initialize
   
End Sub

Public Sub Add_XY (X As Int, Y As Int)

    ListX.add(X)
    ListY.Add(Y)
   
    'Mark the range of motion on the X axis
    If X > MaxX Then MaxX = X
    If X < MinX Then MinX = X

    'Mark the range of motion on the Y axis
    If Y > MaxY Then MaxY = Y
    If Y < MinY Then MinY = Y
   
    'Connect the last two points

End Sub

 

[Gary Milne]

I'm writing my first class in B4A. It will basically create a list of all of the points touched. I call the Initialize method and it works as expected. I then call Add_XY and I get an error because the ListX is Null.

I'm sure it's simple but it's not obvious to me what I need to do for this to work.

Any pointers appreciated.

'Class module
Sub Class_Globals
    Public MaxX As Int
    Public MinX As Int
    Public MaxY As Int
    Public MinY As Int
    Public ListX As List
    Public ListY As List
  
End Sub

'Initializes the object. You can add parameters to this method if needed.
Public Sub Initialize (X As Int, Y As Int)
    MinX = X
    MaxX = X
    MinY = Y
    MaxY = Y
  
    ListX.Initialize
    ListY.Initialize
  
End Sub

Public Sub Add_XY (X As Int, Y As Int)

    ListX.add(X)
    ListY.Add(Y)
  
    'Mark the range of motion on the X axis
    If X > MaxX Then MaxX = X
    If X < MinX Then MinX = X

    'Mark the range of motion on the Y axis
    If Y > MaxY Then MaxY = Y
    If Y < MinY Then MinY = Y
  
    'Connect the last two points

End Sub

I figured out the answer. I was declaring instance of the class on a panel_touch event and then gathering the points as the user dragged on the canvas. I moved the declaration up to the Globals area and then everything worked as expected.