gridwidget.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from __future__ import (division, absolute_import, print_function,
                        unicode_literals)

import os
import sys

# These are only needed for Python v2 but are harmless for Python v3.
import sip
sip.setapi('QString', 2)
sip.setapi('QVariant', 2)

from PyQt4 import QtCore, QtGui, uic


class ContainerWidget(QtGui.QWidget):
    def __init__(self, parent=None):
        super(ContainerWidget, self).__init__(parent)

        self.layout = QtGui.QHBoxLayout(self)
        self.layout.setContentsMargins(0, 0, 0, 0)
        self.layout.setSpacing(0)

        self.containedWidget = None

    def setContainedWidget(self, widget):
        self.containedWidget = widget
        if widget:
            widget.setParent(self)
            self.layout.addWidget(widget)

    def cloneAndPassContainedWidget(self):
        cloned = ContainerWidget(self.parent())
        cloned.setContainedWidget(self.containedWidget)
        self.setContainedWidget(None)
        return cloned


class GridWidget(QtGui.QTableWidget):
    def resizeEvent(self, event):
        total_width = self.viewport().width()
        nb_columns = self.columnCount()

        for column in range(nb_columns):
            self.horizontalHeader().resizeSection(column,
                                                  total_width / nb_columns)

    def posToRowCol(self, pos):
        index = self.indexAt(pos)
        if not index:
            return None
        return (index.row(), index.column())

    def dropEvent(self, event):
        if event.source() == self and \
           (event.dropAction() == QtCore.Qt.MoveAction or
           self.dragDropMode() == QtGui.QAbstractItemView.InternalMove):

            destPos = self.posToRowCol(event.pos())
            if destPos:
                index = self.selectedIndexes()[0]

                widget = self.cellWidget(index.row(), index.column())
                if widget:
                    cloned_widget = widget.cloneAndPassContainedWidget()
                    self.setCellWidget(destPos[0], destPos[1], cloned_widget)
                    self.removeCellWidget(index.row(), index.column())

                    event.accept()
                    event.setDropAction(QtCore.Qt.CopyAction)

        super(GridWidget, self).dropEvent(event)

    def addWidget(self, row, col, widget):
        container_widget = ContainerWidget(self)
        container_widget.setContainedWidget(widget)
        self.setCellWidget(row, col, container_widget)

    def firstEmptyCell(self):
        empty_cell = (-1, -1)
        for row in range(self.rowCount()):
            for column in range(self.columnCount()):
                if not self.cellWidget(row, column):
                    empty_cell = (row, column)
                    break

            if empty_cell != (-1, -1):
                break

        if empty_cell == (-1, -1):
            self.insertRow(self.rowCount())
            empty_cell = (self.rowCount() - 1, 0)

        return empty_cell


class CustomWidget(QtGui.QLabel):
    def __init__(self, parent=None):
        super(CustomWidget, self).__init__(parent)
        self.setStyleSheet('background-color: red; color: yellow;')


TestPanelUi = uic.loadUiType(os.path.join(os.path.dirname(__file__),
                                          'gridwidget.ui'))[0]


class TestPanel(QtGui.QMainWindow, TestPanelUi):
    def __init__(self):
        super(TestPanel, self).__init__()
        self.setupUi(self)
        self.pushButton.clicked.connect(self.addWidget)

        self.counter = 0

    @QtCore.pyqtSlot()
    def addWidget(self):
        self.counter += 1

        widget = CustomWidget(self.gridWidget)
        widget.setText('Widget {}'.format(self.counter))

        row, col = self.gridWidget.firstEmptyCell()
        self.gridWidget.addWidget(row, col, widget)


def main():
    app = QtGui.QApplication(sys.argv)

    panel = TestPanel()
    panel.show()

    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

gridwidget.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>800</width>
    <height>600</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Drag and drop widgets !</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <layout class="QHBoxLayout" name="horizontalLayout">
    <item>
     <widget class="QPushButton" name="pushButton">
      <property name="text">
       <string>Add a widget</string>
      </property>
     </widget>
    </item>
    <item>
     <widget class="GridWidget" name="gridWidget">
      <property name="editTriggers">
       <set>QAbstractItemView::NoEditTriggers</set>
      </property>
      <property name="dragEnabled">
       <bool>true</bool>
      </property>
      <property name="dragDropOverwriteMode">
       <bool>false</bool>
      </property>
      <property name="dragDropMode">
       <enum>QAbstractItemView::InternalMove</enum>
      </property>
      <property name="rowCount">
       <number>3</number>
      </property>
      <property name="columnCount">
       <number>3</number>
      </property>
      <attribute name="horizontalHeaderVisible">
       <bool>false</bool>
      </attribute>
      <attribute name="verticalHeaderVisible">
       <bool>false</bool>
      </attribute>
      <row/>
      <row/>
      <row/>
      <column/>
      <column/>
      <column/>
     </widget>
    </item>
   </layout>
  </widget>
 </widget>
 <customwidgets>
  <customwidget>
   <class>GridWidget</class>
   <extends>QTableWidget</extends>
   <header>gridwidget</header>
  </customwidget>
 </customwidgets>
 <resources/>
 <connections/>
</ui>