You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: focus_manager.go
    path of file: ./repos/fyne/internal/app
    
    the code of the file until where you have to start completion: package app

import (
	"sync"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/internal/driver"
)

// FocusManager represents a standard manager of input focus for a canvas
type FocusManager struct {
	sync.RWMutex

	content fyne.CanvasObject
	focused fyne.Focusable
}

// NewFocusManager returns a n
    
func (f *FocusManager) Focus(obj fyne.Focusable) bool {
	f.Lock()
	defer f.Unlock()
	if obj != nil {
		var hiddenAncestor fyne.CanvasObject
		hidden := false
		found := driver.WalkCompleteObjectTree(
			f.content,
			func(object fyne.CanvasObject, _, _ fyne.Position, _ fyne.Size) bool {
				if hiddenAncestor == nil && !object.Visible() {
					hiddenAncestor = object
				}
				if object == obj.(fyne.CanvasObject) {
					hidden = hiddenAncestor != nil
					return true
				}
				return false
			},
			func(object fyne.CanvasObject, pos fyne.Position, _ fyne.CanvasObject) {
				if hiddenAncestor == object {
					hiddenAncestor = nil
				}
			},
		)
		if !found {
			return false
		}
		if hidden {
			return true
		}
		if dis, ok := obj.(fyne.Disableable); ok && dis.Disabled() {
			type selectableText interface {
				SelectedText() string
			}
			if _, isSelectableText := obj.(selectableText); !isSelectableText || fyne.CurrentDevice().IsMobile() {
				return true
			}
		}
	}
	f.focus(obj)
	return true
}