Grid selection

Posted on April 15, 2020

If you’ve ever used wxGrid, you probably must have had some questions about the handling of the selection in its API. The class provides several methods, such as GetSelectedCells(), GetSelected{Rows,Cols} and GetSelectionBlock{TopLeft,BottomRight}() and it’s not always clear when each of them should be used and what do they return and, especially, what they don’t return.

The bad news is that now there is one more method, GetSelectedBlocks(). But the good news is that the new method replaces all of the previous ones, can be called in any grid selection mode and always returns all the selected cells, whether they’re selected individually or as parts of rows, columns or blocks. And, as an extra bonus, this method is also more convenient to use from C++11 code as it returns an object that can be iterated over range-based for loops:

    for ( const auto block: grid->GetSelectedBlocks() ) {
        // Handle the block, e.g. check if it touches the given area.
        if ( block.Intersects(myBlock) ) {
            ...
            break;
        }
    }

The type of block in the loop above is wxGridBlockCoords, which is a very simple class containing 4 integers describing the block top-left and bottom-right corners. It provides a couple of useful operations such as Intersects() shown above or Contains(), but mostly you would just use its simple accessors to get the cells covered by this block, e.g.

        if ( block.GetLeftCol() == 0 &&
                block.GetRightCol() == grid->GetNumberCols() - 1 ) {
            // This block contains rows from block.GetTopRow() to
            // block.GetBottomRow() inclusive -- possibly just one of them.
        }

Note that you can still use wxGrid::IsInSelection() to just check if the given cell is selected, but for any other use of the selection, and in particularly if you need to operate on the entire rows or columns, you use wxGrid::GetSelectedBlocks() from now on – i.e. starting with wxWidgets 3.1.4.

Finally, as part of the work on improving grid selection handling, its user-visible behaviour has also been completely overhauled and enhanced in too many ways to list here but, to summarize, the various combinations involving Shift, Ctrl and cursor arrow or space keys now work as expected in all grid selection modes and so does clicking on row or column headers and even using both of them together, whereas previously this could result in quite interesting, to put it mildly, and rather unpredictable, selection changes.

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