title: How to fix 'GLib-GObject-WARNING / CRITICAL'
body: <p>i'm writing some code in Qt, and when I use QColorDialog there is a freeze of the application with the following output:</p>
  
  <pre><code>GLib-GObject-WARNING **: 10:53:36.573: cannot register existing type 'GtkWidget'
  
  GLib-GObject-WARNING **: 10:53:36.573: cannot add class private field to invalid type '&lt;invalid&gt;'
  
  GLib-GObject-WARNING **: 10:53:36.573: cannot add private field to invalid (non-instantiatable) type '&lt;invalid&gt;'
  
  GLib-GObject-CRITICAL **: 10:53:36.573: g_type_add_interface_static: assertion 'G_TYPE_IS_INSTANTIATABLE (instance_type)' failed
  
  GLib-GObject-WARNING **: 10:53:36.573: cannot register existing type 'GtkBuildable'
  
  GLib-GObject-CRITICAL **: 10:53:36.573: g_type_interface_add_prerequisite: assertion 'G_TYPE_IS_INTERFACE (interface_type)' failed
  
  GLib-CRITICAL **: 10:53:36.573: g_once_init_leave: assertion 'result != 0' failed
  
  GLib-GObject-CRITICAL **: 10:53:36.573: g_type_add_interface_static: assertion 'G_TYPE_IS_INSTANTIATABLE (instance_type)' failed
  
  GLib-GObject-CRITICAL **: 10:53:36.573: g_type_register_static: assertion 'parent_type &gt; 0' failed
  
  GLib-GObject-WARNING **: 10:53:36.573: cannot add private field to invalid (non-instantiatable) type '&lt;invalid&gt;'
  </code></pre>
  
  <p>I tried the same code in a blank project and it works. I'm using this code to display the QColorDialog:</p>
  
  <pre><code>QColor m_color;
  m_color = QColorDialog::getColor(m_color, this, QString(), QColorDialog::DontUseNativeDialog);
  </code></pre>
  
  <p>I've already tried to clean QtCreator cache deleting /home/user/.config/QtProject and I've already tried to delete .pro.user file in the project</p>
  
  <p>I've tried to run on both Debian 9 and Linux Mint 19.1 Cinnamon, same problem.</p>