From the code you linked to, it looks like you have a reference to the buttons that you have added. If you want to manipulate them, you'll need to set them up as global variables (which they are in the code). You can then set the Enabled state directly. :
In addition to previous replies, an example Sub to set Button Enabled property using an Array of Global Button Node(s). Note: the toolbar example includes other than Button nodes, so a Button node needs to be determined.
The Button Array is populated depending the action required as set by the tabpanel, i.e. examples
Action1 = disable Buttons 1 and 2
B4X:
Dim Btns() As Button = Array As Button(tbButton1,tbButton2)
EnableButtons(Btns, False)
Action2 = enable Button 2
B4X:
Dim Btns() As Button = Array As Button(tbButton2)
EnableButtons(Btns, True)
Sub Enable or disable Buttons
B4X:
Sub EnableButtons(Btns() As Button, Enabled As Boolean)
Dim ButtonList As List = joToolbar.RunMethodJO("getItems", Null)
For Each n As Node In ButtonList
If n Is Button Then
Dim btn As Button = n
For Each b As Button In Btns
If b = btn Then btn.Enabled = Enabled
Next
End If
Next
End Sub
Sub EnableButton( TagText As String, Enabled As Boolean)
Dim ButtonList As List = joToolbar.RunMethodJO("getItems", Null)
For Each n As Node In ButtonList
If n Is Button Then
Dim btn As Button = n
If btn.Tag = TagText Then btn.Enabled = Enabled
End If
Next
End Sub