Calling custom class in .ui file fails

Question

I get this error when I try to refer to my custom class from .ui file. What's wrong with what I do?

"QFormBuilder was unable to create a custom widget of the class 'TimelinePane'; defaulting to base class 'QWidget'." 

QWidget pops up with the layout I'm specifying in .ui file. Problem is just the custom class.

To add the custom class' description, I modified .ui file manually (added the entire <customwidgets> section), which is why I have to open a new question since I haven't found the same Q yet. I suspect the path of the class in .ui file but none of the options I tried (see the part I commented out) worked. I also guess that using python should not be the matter here but am not entirely sure. Haven't tried C++ yet.

from PySide import QtGui  
from PySide import QtCore
from PySide import QtUiTools

class MyWidget(QtGui.QMainWindow):
    def __init__(self, *args):  
       apply(QtGui.QMainWindow.__init__, (self,) + args)

       loader = QtUiTools.QUiLoader()
       file = QtCore.QFile('./src/prove_qt_ui_file/prove_main_widget.ui') 
       file.open(QtCore.QFile.ReadOnly)
       self.myWidget = loader.load(file, self)
       file.close()
       self.setCentralWidget(self.myWidget)

if __name__ == '__main__':  
   import sys  
   import os
   print("Running in " + os.getcwd() + " .\n")
   app = QtGui.QApplication(sys.argv)  
   win  = MyWidget()  
   win.show()
   app.exec_()

prove_main_widget.ui

<?xml version="1.0" encoding="UTF-8" ?>
<ui version="4.0">
 <class>MyWidget</class>
 <widget class="QWidget" name="MyWidget">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>687</width>
    <height>698</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Runtime Monitor</string>
  </property>
  <layout class="QVBoxLayout">
   <property name="spacing">
    <number>0</number>
   </property>
   <property name="margin">
    <number>0</number>
   </property>
   <item>
    <widget class="QSplitter" name="splitter">
     <property name="orientation">
      <enum>Qt::Vertical</enum>
     </property>
     <property name="handleWidth">
      <number>9</number>
     </property>
     <widget class="QTreeWidget" name="warn_tree">
      <attribute name="headerVisible">
       <bool>false</bool>
      </attribute>
      <column>
       <property name="text">
        <string notr="true">1</string>
       </property>
      </column>
     </widget>
     <widget class="QTreeWidget" name="tree_all_devices">
      <attribute name="headerVisible">
       <bool>false</bool>
      </attribute>
      <column>
       <property name="text">
        <string notr="true">1</string>
       </property>
      </column>
     </widget>
     <widget class="TimelinePane" name="timeline_pane" native="true">
      <property name="minimumSize">
       <size>
        <width>0</width>
        <height>80</height>
       </size>
      </property>
      <property name="whatsThis">
       <string extracomment="Timeline"/>
      </property>
     </widget>
    </widget>
   </item>
  </layout>
 </widget>
 <customwidgets>
  <customwidget>
   <class>TimelinePane</class>
   <extends>QWidget</extends>
<!--   <header>timeline_pane</header> --> <!-- NG -->
<!--   <header>prove_qt_ui_file.timeline_pane</header> --> <!-- NG -->
   <header>src.prove_qt_ui_file.timeline_pane</header>  <!-- NG -->
  </customwidget>
 </customwidgets>
 <resources/>
 <connections/>
</ui>

timeline_pane.py

from PySide.QtGui import QWidget, QGraphicsScene, QGraphicsView, QColor, QHBoxLayout, QPushButton
class TimelinePane(QWidget):
    def __init__(self, parent):
        super(TimelinePane, self).__init__()
        print '\tTimelinePane init 1' # This doesn't print.

(Environment) Ubuntu 12.04, python 2.7.3

Answer 1

In theory, to have your custom widget work you should only have to call:

loader.registerCustomWidget(TimelinePane)

before calling loader.load(). You need to add the relevant import statements, in your case:

from timeline_pane import TimelinePane

However, I just tested this with PySide 1.1.2 on Ubuntu 12.04 x86_64, and it caused a segfault. YMMV, so please test.

I ended up implementing this workaround: http://www.mail-archive.com/[e-mail]/msg00306.html

In short, override the QUiLoader's creteWidget() method, and if the class_name of the widget is not in self.availableWidgets(), instantiate it yourself according to the customWidgets instance variable that you've added.

BTW, you can also make use of the right-click "Promote To" functionality in the Qt Designer instead of editing the ui file directly.