在表格上滚动并在底部完成时,将单元格添加到表格视图

我在UIViewController中有一个tableView。当我加载viewController时,正在加载带有3个单元格的tableView。每次我在tableView上滚动并在其底部完成时,我都希望添加到它(其他)3个单元格中。facebook应用程序是如何做到的!请帮帮我!这是我在代码中所经历的(未添加单元格):

    -(void) tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
    {
        //I created an int flag because this method (as soon as it initialize the 
        //table) is called 2 times (because when it load the viewController, is called
        // the method that populates the arrays that contain the details to be shown in
        // the cells and reload the tableView)
        if (_flagCells == 0 || _flagCells == 1) {
            _flagCells ++;
            return;
        }

        if([indexPath row] == ((NSIndexPath*)[[tableView indexPathsForVisibleRows] lastObject]).row){

//phpClass is a class that contain scripts used to connect my app to script php for mySQL DB 
//objsRequest is a method of phpClass that receive a query for input and return an array of //results of that query. cellsLimit represent the cells to be shown (Once every 3 to 3) and //numberOfDequeuedCells represent the number of cells to be added (every 3) that is SELECT .. //FROM .. LIMIT 0,3 .... LIMIT 3,3 .... LIMIT 6,3 ....           
[_arrID addObjectsFromArray:[_phpClass objsRequest:[NSString stringWithFormat:@"SELECT ID FROM mii LIMIT %d,%d",_cellsLimit,_numberOfDequeuedCells]]];

            for (int i = (int)[_arrID count]-3; i < [_arrID count]; i++) {

//objRequest is a method of phpClass that receive a query for input and return a string that 
//represent the result of that query
                [_arrNames addObject:[_phpClass objRequest:[NSString stringWithFormat:@"SELECT Name FROM mii WHERE ID = %@",_arrID[i]]]];
                [_arrGen addObject:[_script objRequest:[NSString stringWithFormat:@"SELECT Gen FROM mii WHERE ID = %@",_arrID[i]]]];

//getImg is a method of phpClass that receive the user ID for input and return an image
//representing the user image
                UIImage *img = [_phpClass getImg:_arrID[i]];
                    [_arrImgs insertObject:img atIndex:i];

//Here is the problem because the rows doesn't be added to my tableView
                [_tableView beginUpdates];
                [_tableView insertRowsAtIndexPaths:@[[NSIndexPath indexPathForRow:i inSection:0]] withRowAnimation:UITableViewRowAnimationAutomatic];

            }
            _cellsLimit +=3;
            [_tableView endUpdates];
        }
    }