Question

I’m figuring out the correct way to reuse cells in a UITableView and I would know if the mechanism I’m using is correct.

The scenario is the following.

I’ve a UITableView that displays a list of data obtained from a web service.

_listOfItems = e.Result as List<Item>;

where _listOfItems is an instance variable.

This list is passed to a class that extends UITableViewSource. Obviously this class override GetCell method to visualize data in this manner:

public override UITableViewCell GetCell (UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath)
{       
    UITableViewCell cell = tableView.DequeueReusableCell(_cID);

    Item item = _listOfItems[indexPath.Row];

    int id = item.Id;

    if (cell == null)
    {   
        cell = new UITableViewCell(UITableViewCellStyle.Value1, _cID);

        cell.Tag = id;

        _cellControllers.Add(id, cell);
    }
    else
    {
        bool vb = _cellControllers.TryGetValue(id, out cell);

        if(vb)
        {
            cell = _cellControllers[id];
        }

        else
        {
            cell = new UITableViewCell(UITableViewCellStyle.Value1,  _cID);             
            cell.Tag = id;

            _cellControllers.Add(id, cell);
        }
    }

    cell.TextLabel.Text = item.Title;

    return cell;
}

where

_cID is an instance variable identifier for the cell

string _cID = "MyCellId";

_cellControllers is a dictionary to store cell and the relative id for an Item instance

Dictionary<int, UITableViewCell> _cellControllers;

I’m using the dictionary to store cells bacause when a row is tapped, I have to retrieve the id for the cell tapped (through cell.Tag value), do some other operation – i.e.retrieve other some data from the service – and then update that cell again with new values. In this case each cell has to be unique.

So, my question is:

Is this the right manner to reuse cell or is it possible to figured out another solution to reuse cell and guaranteeing each tap for a cell is unique?

I hope it’s all clear 🙂 Thank you in advance. Regards.

Answer 1

I think what you are doing here is a bit too much. Especially the part where you are holding extra references to cells in a Dictionary.

I would do it differently. The DequeueReusableCell method is there so that you can retrieve any existing cell, but not necessarily the values it contains. So something like this will suffice:

public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
{

    int rowIndex = indexPath.Row;
    Item item  = _listOfItems[rowIndex];

    UITableViewCell cell = tableView.DequeueReusableCell(_cID);

    if (cell == null)
    {
        cell = new UITableViewCell(UITableViewCellStyle.Value1, _cID);
    }

    // Store what you want your cell to display always, not only when you are creating it.
    cell.Tag = item.ID;
    cell.TextLabel.Text = item.Title;

    return cell;
}

Then, in the RowSelected method, change your data source:

public override void RowSelected (UITableView tableView, NSIndexPath indexPath){
    // Do something here to change your data source _listOfItems[indexPath.Row] = new Item();
}

If I understand correctly what you want to do, this solution is better.