Here’s sample code that shows how to reselect cells after rows or columns have been added/removed from a matrix. This issue pops up when you enclose a matrix in a scroll view and then you would like the matrix’s width to fit the content width of the scroll view. If you resize the matrix while also enforcing a minimum cell width, you will have to add and delete rows and columns accordingly. If you would like the state of each cell to persist after rows/columns have been added/removed, you have to record the indicies of the selected cells before the matrix’s row/column count is altered and then reselect the cells after rows/columns have been added/removed.

This sample code is for a custom matrix method that adds/removes rows/columns when its enclosing scroll view’s content size changes.

• (void)resizeMatrix { NSArray *selectedCells = [self selectedCells]; NSMutableIndexSet *indexSet = [[[NSMutableIndexSet alloc] init] autorelease]; unsigned int i, selectedCellCount = [selectedCells count]; NSArray *cells = [self cells]; for (i = 0; i < selectedCellCount; i++) { [indexSet addIndex:[cells indexOfObject:[selectedCells objectAtIndex:i]]]; } selectedCellCount = [indexSet count];

    /*
      
           add/remove rows/columns here
  
    */
  

  [self deselectAllCells]; i = [indexSet firstIndex]; do [self setSelectionFrom:i to:i anchor:i highlight:YES]; while ((i = [indexSet indexGreaterThanIndex:i]) != NSNotFound);

}

–zootbobbalu