[tableView visibleCells]

-(NSArray *)cellsForTableView:(UITableView *)tableView
{
    NSInteger sections = tableView.numberOfSections;
    NSMutableArray *cells = [[NSMutableArray alloc]  init];
    for (int section = 0; section < sections; section++) {
        NSInteger rows =  [tableView numberOfRowsInSection:section];
        for (int row = 0; row < rows; row++) {
            NSIndexPath *indexPath = [NSIndexPath indexPathForRow:row inSection:section];
            UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];   // **here, for those cells not in current screen, cell is nil**
            [cells addObject:cell];
        }
    }
    return cells;
}

func getAllCells() -> [UITableViewCell] {

    var cells = [UITableViewCell]()
    // assuming tableView is your self.tableView defined somewhere
    for i in 0...tableView.numberOfSections-1
    {
        for j in 0...tableView.numberOfRowsInSection(i)-1
        {
            if let cell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: j, inSection: i)) {

               cells.append(cell)
            }

        }
    }
 return cells
 }

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    CustomCell *Cell = [self dequeueReusableCellWithIdentifier:@"Custom_Cell_Id"];
    if (Cell == NULL)
    {
        Cell = [[CustomCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"Custom_Cell_Id"]];
        [Cells_Array addObject:Cell];
    }
}

- (void) DoSomething
{
    for (int i = 0;i < [Cells count];i++)
    {
        CustomCell *Cell = [Cells objectAtIndex:i];
        //Access cell components
    }
}

-(UITableViewCell) cellForRowAtIndexPath (NSIndexPath *)indexPath

/// Reference to all cells.
private var allCells = Set<UITableViewCell>()

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Your_Cell_ID") as! UITableViewCell
    if !allCells.contains(cell) { allCells.insert(cell) }
    return cell
}

extension UITableViewDataSource where Self:UITableView {
   /**
    * EXAMPLE: tableView.cells//list of cells in a tableview
    */
   var cells:[UITableViewCell] {
       return (0..<self.numberOfSections).indices.map { (sectionIndex:Int) -> [UITableViewCell] in
           return (0..<self.numberOfRows(inSection: sectionIndex)).indices.compactMap{ (rowIndex:Int) -> UITableViewCell? in
               return self.cellForRow(at: IndexPath(row: rowIndex, section: sectionIndex))
         }
       }.flatMap{$0}
    }
}

self.tableView.frame = CGRectMake(self.tableView.frame.origin.x, self.tableView.frame.origin.y, self.tableView.contentSize.width, self.tableView.contentSize.height);

-(NSMutableArray *)cellsForTableView:(UITableView *)tableView
  {
  NSMutableArray *cells = [[NSMutableArray alloc]  init];

//Need to total each section
for (int i = 0; i < [tableView numberOfSections]; i++)
{
    NSInteger rows =  [tableView numberOfRowsInSection:i];
    for (int row = 0; row < rows; row++) {
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:row inSection:i];
        UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
        for (UIView *subView in cell.subviews)
        {
            if ([subView isKindOfClass:[UITextField class]]){
                UITextField *txtField = (UITextField *)subView;
                [cells addObject:txtField.text];

            }
        }

    }

}
return cells;

-(void) reloadViewHeight
 {
    float currentTotal = 0;

//Need to total each section
for (int i = 0; i < [self.tableView numberOfSections]; i++)
{
    CGRect sectionRect = [self.tableView rectForSection:i];
    currentTotal += sectionRect.size.height;
}

//Set the contentSizeForViewInPopover
self.contentSizeForViewInPopover = CGSizeMake(self.tableView.frame.size.width, currentTotal);