Set rowSpan or colSpan of a child of a GridLayout programmatically?

I have a GridLayout with 5 columns and 3 rows. Now I can insert arbitrary child views, which is great. Even better is, that I can assign columnSpan=2 to some item in order to span it to 2 columns (the same with rowSpan).

The problem now is, that I cannot assign rowSpan or columnSpan programmatically (i.e. at runtime). Some search suggested something like this:

layoutParams.columnSpec = GridLayout.spec(0, columnSpan);

But I don't quite understand what the parameters of spec mean (start and size). The documentation is also quite poor at this point.

Any help is highly appreciated!