Reports

Use GtkHeaderBarset_custom_title which can be any widget. Here is pygtk example.

import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk

class HeaderEg(Gtk.Window):
    def __init__(self):
        Gtk.Window.__init__(self)
        self.eNtry = Gtk.Entry()
        self.set_default_size(-1, 200)
        self.connect("destroy", Gtk.main_quit)
        headerbar = Gtk.HeaderBar()
        headerbar.set_custom_title(self.eNtry)
        headerbar.set_show_close_button(True)
        self.set_titlebar(headerbar)


window = HeaderEg()
window.show_all()
Gtk.main()

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