Mac OS X - Canvas doesn't redraw after RequestFile

Import mojo2

Import brl.requesters

Class MyApp Extends App
	Field canvas:Canvas
	Field txt: String = "Hello World"

    Method OnCreate()
    	canvas=New Canvas
  
    End
    
    Method OnUpdate()
    	If MouseHit(MOUSE_LEFT) Then
	      Local filter:="Image Files:png,jpg,bmp;Text Files:txt;All Files:*"
	        Local file:=RequestFile( "Select graphic file to open",filter )
	        If file txt = file
    	End
    End
    
	Method OnRender()
	
		canvas.Clear 0,0,1
		
		canvas.SetBlendMode 3
		canvas.SetColor 0,0,0,.5
		canvas.DrawText txt,DeviceWidth/2+2,DeviceHeight/2+2,.5,.5
		
		canvas.SetBlendMode 1
		canvas.SetColor 1,1,0,1
		canvas.DrawText txt,DeviceWidth/2,DeviceHeight/2,.5,.5
		
		canvas.SetColor(1,0,0)
		canvas.DrawRect(MouseX, MouseY, 32, 32)
		
		canvas.Flush
	End
            
End

Function Main()

    New MyApp

End

static void beginPanel(){
	keyWin=[NSApp keyWindow];
//	if( !keyWin ) [NSApp activateIgnoringOtherApps:YES];
}