Little Problem

[Tricker]

I put this script above Main

class Window_Blah < Window_Base
  
  def initialize
    super(0,0, 599, 329)
    self.contents = Bitmap.new(width - 32, height - 32)
    refresh
  end
  
  def refresh
    self.contents.clear
    self.contents.draw_text(x,y,155,155,"This is some text",1)
  end
end

And this script call in a map event

Window_Blah.new

But why after a bit of seconds the window disappears ?
And how can I make the window disappear when a switch is false ?