I am looking for a way to create an infinite view on a model that is not initialized completely. I would like to create something similar to an Excel spreadsheet, and all I came in was to start with an initialized model (e.g. 100x100 empty cells, maybe working on a database that has empty values), and then just dynamically add next rows/columns (and update view) once we are close to the end of a scrollbar.
But I am wondering if it is the best solution - I think I would definitively benefit from a model that's filled in only partially - by that, I mean store information in the model only about filled cells, and let view handle showing 'empty cells' (which would have been created once we - for example - click them). I know it would be necessary to store XY positions and cell data (instead of only a 2D container with data), but I would like to try different solutions:
And for both solutions, I would like to dynamically allocate more place once data is written.
So there is my question - how can it be achieved with QT model/view programming, if it is even possible to show 'ghost cells' without a model filled with empty data? It would be also nice if I could get a brief explanation of how it is done in apps like excel etc.
Well, your table will never be truly infinite unless you implement some indexing with numbers with infinite digit count and in that case, you will probably not be able to use Qt classes.
But I think you should choose some big enough number to define the maximum. It can be a really large number... if you are on a 64-bit machine, then your 'infinite' table can have 9,223,372,036,854,775,807 rows and the same number of columns. This big number happens to be the maximum of signed 64-bit int. And int is used for indexing with QModelIndex in QAbstractItemModel. So you can have a total of 8.5070592e+37 cells in your two-dimensional 'Excel' table. If this table size is not big enough for you then I do not know what is. Just for comparison, there are approximately 7e+27 atoms in the average human body, maybe a bit more after the covid lockdowns because people were eating instead of practicing sports. :) So you can count all atoms of all people on this planet (say there are a bit less than 10e+10 people altogether). But you will need to buy a bit bigger computer for this task.
So if you decide to go this way, then you can easily override QAbstractTableModel and display it in QTableView. Of course, you cannot save the underlying data in a two-dimensional array because you do not have enough memory. But you have to choose some other method. For example a QHash<QPoint, QString> where QPoint will represent the coordinates and QString the value (you can choose any other type instead of a string of course). Then when you will want to get the value for the given coordinates, you just look up the value in the hash table. The number of data points you will be able to hold depends only on your memory size. This solution is very simple, I guess it will be some 30 rows of code, not more.