使andlabs.ui窗口不可调整大小

Question

I am using following code to create a simple window:

package main
import ("github.com/andlabs/ui")

func main() {
    ui.Main(makeMainWin)
}

func makeMainWin(){
    var box = ui.NewVerticalBox()
    box.Append(ui.NewLabel("Label1"), false)
    box.Append(ui.NewLabel("Label2"), false)
    box.Append(ui.NewLabel("Label3"), false)

    var mainWindow = ui.NewWindow("Hello", 200, 100, false)
    mainWindow.SetChild(box)
    mainWindow.OnClosing( func (*ui.Window) bool { ui.Quit(); return true })
    mainWindow.Show()
}

However, I want this window to be non-resizable. How can this be done? I could not find the method for this on searching the net including this page: https://github.com/andlabs/ui/blob/master/window.go