How to set window position and make it unresizable in Go walk - user-interface

Question

I am trying to figure out the basics of working with the Go GUI library, walk.
For starters, I would like to be able to
Control the window's position
hopefully in a way similar to what other languages provide (center on screen, center to parent, exact coordinates etc).
Make the window unresizable
This is the code I have, I was hoping the MaxSize declaration would solve the second problem, but it doesn't, and I was looking for some sort of a Position declaration but couldn't find anything that makes sense to me.
package main
import (
// "github.com/lxn/walk"
. "github.com/lxn/walk/declarative"
)
func main() {
MainWindow{
Title: "Test",
MinSize: Size{300, 50},
MaxSize: Size{300, 50}, // Doesn't work
// Position: ... // Doesn't exist
Layout: VBox{},
Children: []Widget{
Label{Text: "Hello World"},
},
}.Run()
}

Answer 1

It looks like walk doesn't provide this functionality in its own API. However, walk created on top of win which actually is just a Go bindings to WinAPI. So you can easily call any WinAPI functions. For example, to show a main window on a specified position one can call SetWindowPos():
package main
import (
"github.com/lxn/win"
"github.com/lxn/walk"
. "github.com/lxn/walk/declarative"
)
const (
SIZE_W = 600
SIZE_H = 400
)
type MyMainWindow struct {
*walk.MainWindow
}
func main() {
mw := new(MyMainWindow)
MainWindow{
Visible: false,
AssignTo: &mw.MainWindow,
}.Create()
defaultStyle := win.GetWindowLong(mw.Handle(), win.GWL_STYLE) // Gets current style
newStyle := defaultStyle &^ win.WS_THICKFRAME // Remove WS_THICKFRAME
win.SetWindowLong(mw.Handle(), win.GWL_STYLE, newStyle)
xScreen := win.GetSystemMetrics(win.SM_CXSCREEN);
yScreen := win.GetSystemMetrics(win.SM_CYSCREEN);
win.SetWindowPos(
mw.Handle(),
0,
(xScreen - SIZE_W)/2,
(yScreen - SIZE_H)/2,
SIZE_W,
SIZE_H,
win.SWP_FRAMECHANGED,
)
win.ShowWindow(mw.Handle(), win.SW_SHOW);
mw.Run()
}
To make window unresizable you need to unset WS_THICKFRAME style, as shown in the example. More information can be found here.