I experience the same error. I am not sure when it started, but the "Class not registered" error comes up during drag-and-drop move operation. As a result the QListView::paintEvent also does not get called. Interestingly when I move out and in the widget still dragging the object the paintEvent function is called. I am using Qt 5.15.3 LTS with the latest fully updated VS2019 Enterprise. This happens when using both x86 and x64 bit builds. I did a full rebuild of my project with all libraries, but the error during drag-and-drop still appears in the debug console window. Some threads suggest that I am using mixed x86/x64 DLLs, but checking all DLLs and binaries report themselves as x86 binaries(respectively x64 in the x64 bit build). (https://stackoverflow.com/questions/1496214/how-to-solve-com-exception-class-not-registered-exception-from-hresult-0x80040) If you have any idea how to detect which module or COM object is causing this error might help. I have not found a way to trace and fix this. Any help is very welcome! Thanks!

@raven-worx said in QTreeView drag/drop "icon" Transparency: @Dariusz the only way currenlty is to start the drag entirely yourself by overwriting QAbstractItemView::startDrag() Its not that hard. Simply get the data for all selected indexes from the model and set a custom drag pixmap and call QDrag::exec() Hey Id love to do it but sadly it does not work. For example > def startDrag(self, supportedActions): d = QDrag(self) data = self.model().mimeData(self.selectedIndexes()) d.setMimeData(data) d.exec_(supportedActions) It Will, not produce the same effect as native action. Simply because when you look at source code where > if (drag->exec(supportedActions, defaultDropAction) == Qt::MoveAction) d->clearOrRemove(); Which handles the items state after their drag. I can not reproduce the action without a large rewrite of the startDrag event I'm afraid. I wish that the function that they use for Pixmap generation > QPixmap pixmap = d->renderToPixmap(indexes, &rect); rect.adjust(horizontalOffset(), verticalOffset(), 0, 0); QDrag *drag = new QDrag(this); drag->setPixmap(pixmap); Would be a virtual function so that I can overwrite it and provide my own pixmap at that level without messing up entire drag Qt logic.

Yo It appears that I was almost there... just need to create a proper drag! def initializeDrag(self, event, option, index): self.dragInitialized = True print("Drag initialized!") drag = QDrag(self) mim = QMimeData() mim.setText("yoyoyooy") drag.setMimeData(mim) val = drag.exec_() print("Return drag val : ", val) self.dragInitialized = False Once thats made, I then have to handle dragEnterEvent on QTreeView and then pass it to proper function from there... yay!

Woah sweet! will do that thanks!

I've wrote 1 treeView/model system last year that had it all re-implemented from scratch, a few days ago I decided to rewrite it to increase performance and relay more on native functions of QT. Which I did and works great but the margin thing is a sticking point. I remember how much work it was before to get it to work properly... took a while as I had to write quite a few functions before I got to the point of margin detection. I'm very surprised there is no margin = (qt code ) + userMarginOverrideVal in the canDrop() function... this would have allowed us to just say, hey add +5 pixels to detection or something like that... Perhaps I should add it to feature request, would posting it in a bug report tracker be a good place? I don't see feature requests and I have no idea how to get the source to compile (Just didn't spend enough time on it) and add it myself & post to qt as commit... As far as I can tell we need like 2 functions, setOverrideMargin(int val) and getOverrideMargin(), skipping setting flag true/false if we want to use it as defaultVal should just be 0... TIA

@raven-worx said in QTreeView/Model drop action - no expand sign ?: Also did you emit the dataChanged() signal on the parent index? I've just read the post. I forgot to correct it. This is what I edit: bool testModel::dropMimeData(const QMimeData *data, Qt::DropAction action, int row, int column, const QModelIndex &parent) { ... Q_EMIT dataChanged(itemFirst.index(),itemLast.index()) } Hmmmm so I tried this, the parent is the object that is in function above. Q_EMIT dataChanged(parent, parent) Now this now "magically" works, I get extra ">" when I drop item on another item... I also learned that I also need to call Q_EMIT layoutChanged({parent}/flag) to update view if I drop items on expanded parent... Ok all good then, thanks! Weird issue o.o

@Joel-Bodenmann Well actually its not super weird. If you active accessibility settings in windows, (on some pads) you can get this for drag & drop to help people where is hard to hold down mouse. :)