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Creating a custom widget in Slicer


A custom widget is a specialization of another widget or a group of widgets working together. Custom widgets are usually created when you need to add new functionality to existing widgets or groups of widgets. If you simply want a collection of widgets in a special configuration it can be easily done in QtDesigner and probably doesn't require to be a custom widget.

In the following we will assume you are familiar with Qt.
Here are some useful links:

Before starting

There are 2 locations where custom widgets can be. You first have to decide where your custom widget should go:

  • CTK: Qt and/or VTK only
  • Slicer3/Libs/qMRMLWidgets: MRML-aware widgets

A good practice is to split (as possible) your custom widget in 2: a QT-only widget and a MRML-aware widget where the MRML-aware widgets inherits from the Qt-only widget. An intermediate level can be added for Qt and VTK widgets.
It is important to keep the widgets basic. If you think someone else can use your custom widget differently, or if someone would need less features than the custom widget currently have, it is probably a good idea to split the widget in 2 widgets linked with an IS-A relationship.

Coding style

The name of the custom widgets must follow the pattern: qMRML[customName][baseQtWidget], where [baseQtWidget] is the name of the qt widget your custom widget inherits from (i.e. ComboBox, Slider, Dialog, Widget...), and [customName] is a descriptive name. Examples:

  • qMRMLLinearTransformSlider
  • qMRMLMatrixqMRMLMatrixWidget


Step by step

  • Create your widget files (.h and .cxx) in the Lib/qMRMLWidgets directory.
    • If you use a .ui file, add it in the Libs/qMRMLWidgets/Resources/UI directory
    • If you use icon files, add them in the Libs/qMRMLWidgets/Resources/Icons directory and update the Libs/qMRMLWidgets/Resources/qMRMLWidgets.qrc file accordingly
  • Update the Libs/qMRMLWidgets/CMakeLists.txt file with your widget files.
    • add the .h and .cxx files in the qMRMLWidgets_SRCS variable
    • add the .h file in the qMRMLWidgets_MOC_SRCS variable
    • if any, add the .ui file in the qMRMLWidgets_UI_SRCS variable
  • compile with your favorite compiler.

Congratulations, you just added a custom widget in Slicer. The widget can now be used anywhere in Slicer.
However the widget doesn't show up in QDesigner, let's create the associated widget plugin for QDesigner.

Create a widget for the designer

For a general presentation to create custom widgets for Qt Designer, see

Step by step

  • Copy paste this template in the Libs/qMRMLWidgets/Plugins directory.
#ifndef __qMRMLCustomWidgetPlugin_h
#define __qMRMLCustomWidgetPlugin_h

#include "qMRMLWidgetsAbstractPlugin.h"

class QMRML_WIDGETS_PLUGIN_EXPORT qMRMLCustomWidgetPlugin : public QObject,
                                public qMRMLWidgetsAbstractPlugin

  qMRMLCustomWidgetPlugin(QObject *_parent = 0);
  QWidget *createWidget(QWidget *_parent);
  QString domXml() const;
  QString includeFile() const;
  bool isContainer() const;
  QString name() const;


Rename the file qMRML[name of your widget]Plugin.h

  • Replace CustomWidget with the name of your widget
  • Copy-paste the following template in the Libs/qMRMLWidgets/Plugins directory.
#include "qMRMLCustomWidgetPlugin.h"
#include "qMRMLCustomWidget.h"

qMRMLCustomWidgetPlugin::qMRMLCustomWidgetPlugin(QObject *_parent)
        : QObject(_parent)


QWidget *qMRMLCustomWidgetPlugin::createWidget(QWidget *_parent)
  qMRMLCustomWidget* _widget = new qMRMLCustomWidget(_parent);
  return _widget;

QString qMRMLCustomWidgetPlugin::domXml() const
  return "<widget class=\"qMRMLCustomWidget\" \

QString qMRMLCustomWidgetPlugin::includeFile() const
  return "qMRMLCustomWidget.h";

bool qMRMLCustomWidgetPlugin::isContainer() const
  return false;

QString qMRMLCustomWidgetPlugin::name() const
  return "qMRMLCustomWidget";

Rename the file qMRML[name of your widget]Plugin.cxx

  • Replace CustomWidget by the name of your widget
  • If the widget is a container, return true</code in the method <code>isContainer().
  • You can customize how the widget is instantiated in the designer by reimplementing the method domxml().
  • Update Libs/qMRMLWidgets/Plugins/CMakeLists.txt by adding your widget plugin files.
    • add the files qMRMLCustomWidgetPlugin.h and qMRMLCustomWidgetPlugin.cxx in the variable qMRMLWidgetsPlugin_SRCS
    • add the file qMRMLCustomWidgetPlugin.h in the variable qMRMLWidgetsPlugin_MOC_SRCS
  • Finally add your widget in the method qMRMLWidgetsPlugins::customWidgets() of the file Libs/qMRMLWidgets/Plugins/qMRMLWidgetsPlugins.h
  • compile

Congratulations, you just added a custom widget in a plugin that can be read by QDesigner. Read the next tutorial to learn how you can use the widget into Qt Designer.
Coding style: For a better code readability, make sure you respect the alphabetical order of the files in CMakeLists.txt.