vala-get_content_area Gtk.Dialog错误：来自不兼容指针类型的赋值

Question

内容Gtk。对话框创建错误：

vala
        var dialog  = new Gtk.Dialog ();
        dialog.set_transient_for (this.window);

        var content = dialog.get_content_area ();
        var hbox    = new Box (Orientation.HORIZONTAL, 8);
        content.pack_start (hbox, false, false, 0);

  

警告：来自不兼容的指针类型[-Wincompatible-pointer-types]的赋值      tmp2 = gtk_dialog_get_content_area（对话）；