UITableView Lags when user scrolling

Question

I'm using Xamarin to develop a mobile app in ios.

The problem is that when you scrolling the UITableView lags and its too slow.

Here my method GetCell:

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

        string identifier = @"PostCell";
        var post = Posts [indexPath.Row];
        PostCellVC postCell = tableView.DequeueReusableCell (identifier) as PostCellVC;
        if (postCell == null)
        {
            postCell = new PostCellVC (identifier);
        }
            postCell.btnComments.SetTitle("0 Comments",UIControlState.Normal);
            postCell.lblDescription.Text = post.PostText;
            postCell.btnComments.SetTitle(string.Format("{0} Comments",post.Comments.Length.ToString()),UIControlState.Normal);
            postCell.btnLikes.SetTitle(post.Likes.ToString() + " Likes",UIControlState.Normal);
            postCell.btnUser.SetTitle(post.UserName.ToString(),UIControlState.Normal);
            postCell.imgLike.Image = UIImage.FromBundle ("Images/likeOn.png");
            var actionSheet = new UIActionSheet ("Share options");
            actionSheet.CancelButtonIndex = 2;
            actionSheet.AddButton ("Facebook");
            actionSheet.AddButton ("Twitter");
            actionSheet.AddButton ("Cancel");
            postCell.lblFecha.Text = GetPrettyDate (post.Date);
            //postCell.btnShare.TouchUpInside += share;
            if (post.PictureUrl != null) {
                postCell.imgPost.Image = LayoutHelper.ImageFromUrl (post.PictureUrl);
            }


        return postCell;

    }

Answer 1

You shouldn't add views or download images in your GetCell method. This method is called repeatedly as the user scrolls the table, if it does any long-running operation, it will lead to laggy scrolling.

The method implementation should be really lightweight. The only things that should be done is to dequeue a reusable cell or create a new one and update the data for that cell.

In your specific case, the lag is cause by downloading a photo from a remote URL. This image download should be lazy loaded. Ideally the download itself occurs in a background thread and once the photo is downloaded, then only thing done in the UI thread is updating the UIImageView with the photo.

A few good resources for anyone experiencing issues like this: https://learn.microsoft.com/en-us/xamarin/ios/user-interface/controls/tables/customizing-table-appearance https://github.com/luberda-molinet/FFImageLoading