QGridLayout - Fixed Number of Rows and Columns

webzoid

Is there any way to force a QGridLayout to adopt a fixed number of rows and columns of equal size?

I'm looking for a way of dragging a QWidget onto the layout, but then allowing it to be resized while snapping to the rows, columns to maintain a regular size.

raven-worx

@webzoid
You could pre-insert fixed sized plain widgets into the grid layout. Those widgets then accept the drop events and place the widget inside them.
I think thats the easiest solution without much "hacking".

webzoid

@raven-worx Thanks for your quick reply.

This sounds ok so far, but, what would happen when I want to resize a widget to cover, say, 3 columns and 2 rows? What would happen to those pre-inserted widgets?

I don't mind having to do a bit of hacking - maybe a QWidget or custom QLayout to do the layout logic would be a more elegant solution?

raven-worx

@webzoid said in QGridLayout - Fixed Number of Rows and Columns:

This sounds ok so far, but, what would happen when I want to resize a widget to cover, say, 3 columns and 2 rows? What would happen to those pre-inserted widgets?

I can't tell you straight from head, but just evaluate it with a small example. If the behavior is not as desired you will have to go with a custom layout. Which might be hard work though.

webzoid

@raven-worx Sorry, I didn't mean to put you on the spot... haha.

I've actually been thinking about a custom layout and that it may not be so difficult. If I could specify a number of rows/columns then I can calculate height/width of each cell so that when a widget is resized, I can dynamically compute its size based on its column/row spans.

I'm sure its not a trivial exercise mind but it seems a cute way of doing it. Google searches tell me that plenty of people have tried before but ultimately failed - maybe this is my time to shine!

raven-worx

@webzoid
:)
Difficulty is relative ;)

webzoid

Ok, so I'm mocking something up using a QTableWidget which, surprisingly, seems to be allowing me to do what I want so far. I can set up a fixed number of rows/columns and I can add widgets to a cell which then can be spanned across cols/rows.

Drag and drop seems to be working nicely, just need to figure out the runtime widget resizing and spanning...

webzoid

Is there any way of preventing a QWidget which has been bound to a QTableWidget cell (using the setCellWidget function) from being destroyed when calling removeCellWidget?

I'm wanting to move a QWidget to another cell, but, when dragging it to another cell (and subsequently calling setCellWidget), the "old" cell still holds a pointer to the widget even though it has been moved to another cell.

webzoid

Ok, so using a blood-and-thunder method, I've managed to achieve what I want but basically, its a crappy solution so I'm going to need to look at another way of doing things.

The QTableWidget is just far too slow when large numbers of rows/columns are used.

VRonin

setCellWidget is notoriously painfully slow. It's not a problem of QTableWidget
Are the widget the same type in all cells?

webzoid

@VRonin Yeah, I appreciate that its an issue with the underlying implementation - my fumbling has had be digging into the QAbstractItemView class and implementing my own setIndexWidget function in a custom QTableView class.

Ultimately, the widgets dropped into the cells will have the same base class but the derivatives will be very different.