read-only
The offsets of the column boundaries in the grid.
The first offset is the offset of the left edge of the left-most tile from the left edge of the interior of the grid's padding (0.0 if the padding is EdgeOffsets.zero). The difference between successive entries is the tile width plus the column spacing.
The last offset is the offset of the right edge of the right-most tile from the left edge of the interior of the grid's padding (less the columnSpacing).
If there are n columns in the grid, there should be n + 1 entries in this list. The right edge of the last column is defined as columnOffsets(n), i.e. the left edge of an extra column.