This sample code permits to make application-wide keyboard shortcuts using AccelGroup and Action Signals in Vala.

accel.vala

[Signal (action = true)]
private signal void change_chat_up ();
[Signal (action = true)]
private signal void change_chat_down ();

public MainWindow () {
  this.init_keyboard_shortcuts ();
}

private void init_keyboard_shortcuts () {
  Gtk.AccelGroup accel_group = new Gtk.AccelGroup ();
  this.add_accel_group (accel_group);
  
  /**
  * Keyboard shortcut for switching to previous/next contact's chatview.
  * FIXME: Ctrl+Up | Ctrl+Down doesn't call these signals.
  **/
  this.change_chat_up.connect (() => {
    var index = this.selected_row.get_index ();
    if (index == 0) { return; }
    var prev_row = this.friendlist.get_row_at_index (index - 1);
    this.friendlist.select_row (prev_row);
  });
  this.change_chat_down.connect (() => {
    var index = this.selected_row.get_index ();
    if (index == 0) { return; }
    var next_row = this.friendlist.get_row_at_index (index + 1);
    this.friendlist.select_row (next_row);
  });

  /**
  * Shortcut for Ctrl+Up: Change the chat view to the previous one.
  **/
  this.add_accelerator ("change-chat-up", accel_group, Gdk.keyval_from_name("Up"),
                        Gdk.ModifierType.CONTROL_MASK, Gtk.AccelFlags.VISIBLE);

  /**
  * Shortcut for Ctrl+Down: Change the chat view to the next one.
  **/
  this.add_accelerator ("change-chat-down", accel_group, Gdk.keyval_from_name("Down"),
                        Gdk.ModifierType.CONTROL_MASK, Gtk.AccelFlags.VISIBLE);
}