Draggable PyQt5 tabs in custom TabWidget work in min example, but not in practice

enjoysmath

Here's the min example code that I put together from other sources found on web.

from PyQt5.QtWidgets import QTabWidget
from PyQt5.QtCore import Qt, QPoint, QMimeData
from PyQt5.QtGui import QPixmap, QRegion, QDrag, QCursor

class TabWidget(QTabWidget):
   def __init__(self, parent=None, new=None):
      super().__init__(parent)
      self.setAcceptDrops(True)
      self.tabBar().setMouseTracking(True)
      self.setMovable(True)
      if new:
         TabWidget.setup(self)

   def __setstate__(self, data):
      self.__init__(new=False)
      self.setParent(data['parent'])
      for widget, tabname in data['tabs']:
         self.addTab(widget, tabname)
      TabWidget.setup(self)
      
   def __getstate__(self):
      data = {
         'parent' : self.parent(),
         'tabs' : [],
      }
      tab_list = data['tabs']
      for k in range(self.count()):
         tab_name = self.tabText(k)
         widget = self.widget(k)
         tab_list.append((widget, tab_name))
      return data
         
   def setup(self):
      pass

   def mouseMoveEvent(self, e):
      if e.buttons() != Qt.RightButton:
         return

      globalPos = self.mapToGlobal(e.pos())
      tabBar = self.tabBar()
      posInTab = tabBar.mapFromGlobal(globalPos)
      print(e.pos())
      index = tabBar.tabAt(e.pos())
      tabBar.dragged_content = self.widget(index)
      tabBar.dragged_tabname = self.tabText(index)
      tabRect = tabBar.tabRect(index)

      pixmap = QPixmap(tabRect.size())
      tabBar.render(pixmap,QPoint(),QRegion(tabRect))
      mimeData = QMimeData()
            
      drag = QDrag(tabBar)
      drag.setMimeData(mimeData)
      drag.setPixmap(pixmap)
      
      cursor = QCursor(Qt.OpenHandCursor)
      
      drag.setHotSpot(e.pos() - posInTab)
      drag.setDragCursor(cursor.pixmap(),Qt.MoveAction)
      drag.exec_(Qt.MoveAction)

   def dragEnterEvent(self, e):
      e.accept()
      #self.parent().dragged_index = self.indexOf(self.widget(self.dragged_index))

   def dragLeaveEvent(self,e):
      e.accept()

   def dropEvent(self, e):
      if e.source().parentWidget() == self:
         return

      e.setDropAction(Qt.MoveAction)
      e.accept()
      tabBar = e.source()
      self.addTab(tabBar.dragged_content, tabBar.dragged_tabname)
   

if __name__ == '__main__':
   from PyQt5.QtWidgets import QWidget, QApplication, QHBoxLayout
   import sys
   
   class Window(QWidget):
      def __init__(self):
   
         super().__init__()
   
         self.dragged_index = None
         tabWidgetOne = TabWidget(self)
         tabWidgetTwo = TabWidget(self)
         tabWidgetOne.addTab(QWidget(), "tab1")
         tabWidgetTwo.addTab(QWidget(), "tab2")
   
         layout = QHBoxLayout()
   
         self.moveWidget = None
   
         layout.addWidget(tabWidgetOne)
         layout.addWidget(tabWidgetTwo)
   
         self.setLayout(layout)

   app = QApplication(sys.argv)
   window = Window()
   window1 = Window()
   window.show()
   window1.show()
   sys.exit(app.exec_())

It demonstrates that the concept works also between windows started from the same application instance.

However, when I deploy this class to my real world scenario. Namely this GUI:

It doesn't work. I've found that tabBar.tabAt(event.pos()) is returning -1 meaning it can't find the tab that I'm pressing on and attempting to drag.

Any intuitive reason why this should be happening in my app and not in the minimal example? My app does nothing fancy, and in particular nothing that would cause this to fail, just a standard application of custom MainWindow and etc widgets.

JonB

@enjoysmath said in Draggable PyQt5 tabs in custom TabWidget work in min example, but not in practice:
This is purely a guess:

  globalPos = self.mapToGlobal(e.pos())
  tabBar = self.tabBar()
  posInTab = tabBar.mapFromGlobal(globalPos)
  print(e.pos())
  index = tabBar.tabAt(e.pos())

How do you know that the globalPos lies within the tabBar? Look at the tab bar's rectangle and see if the mouse pos really does lie inside it? Similarly, are there any "gaps"/"areas" in the tab bar such that a mouse pos does not actually lie in a particular tab? I would debug out those position coordinates and compare to what's actually occupied by your tab bar/tabs, to understand what is going on.

enjoysmath

   def mouseMoveEvent(self, e):
      if e.buttons() != Qt.RightButton:
         return

      globalPos = self.mapToGlobal(e.pos())
      tabBar = self.tabBar()
      posInTab = tabBar.mapFromGlobal(globalPos)
      index = tabBar.tabAt(posInTab)
      tabBar.dragged_content = self.widget(index)
      tabBar.dragged_tabname = self.tabText(index)
      tabRect = tabBar.tabRect(index)

      pixmap = QPixmap(tabRect.size())
      tabBar.render(pixmap,QPoint(),QRegion(tabRect))
      mimeData = QMimeData()
            
      drag = QDrag(tabBar)
      drag.setMimeData(mimeData)
      drag.setPixmap(pixmap)
      
      cursor = QCursor(Qt.OpenHandCursor)
      
      drag.setHotSpot(posInTab)
      drag.setDragCursor(cursor.pixmap(),Qt.MoveAction)
      drag.exec_(Qt.MoveAction)

Replace code with this code. In particular we don't take e.pos() except once at the top, then we use globalPos for computing poosInTab, then drag.setHotSpot(posInTab). It works!