B4J Question How to instantly invalidate/draw canvas

[kimstudio]

In B4J I found the canvas will not update instantly in a sub if there are following codes, for following example, how can the canvas update before run into for loop?
If I put sleep in between then it updates but is this the correct way? In old win32 time we have postmessage to release control to event loop to update UI.

sub button1_click
    func_a 
end sub

sub func_a
    canvas.draw
    canvas.invalidate
    'sleep(10)   '-- if I put this then it can update before run into for loop
    for i = 1 to 1000000000000000
          calc
    next
end sub

 

[MicroDrie]

Read what Erel wrote in a similar question: B4J Question force a view to visually refresh NOW

 

[Erel]

Put the sleep inside the loop.