Delete dynamic cell in GetCell method - ios

Question

I am trying trying to remove a cell from the UITableView if the image for the cell is a bad image. Basically my code does a threadPool call for each cell's image to make the flow of binding the data as a user scroll smooth as so inside the GetCell method:
public override UITableViewCell GetCell (UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath)
{
//other stuff
ThreadPool.QueueUserWorkItem(new WaitCallback(RetrieveImage),(object)cell);
}
within that asynchronous method I call the cell.imageUrl property and bind it to an NSData object as so:
NSData data = NSData.FromUrl(nsUrl); //nsUrl is cell.imageUrl
From there I know that if data==null then there was a problem retrieving the image so I want to remove it. What I currently do is set the hidden property to true, but this leaves a blank space. I want to remove the cell entirety so the user won't even know it existed.
I can't set the cell height to 0 because I don't know if the imageUrl is bad until that indexrowpath initiates getcell call. I don't want to just check all images from the data thats binded to the UITableView because that would be a big performance hit since it can be easily a hundred items. I am currently grabbing the items from a webservice that gives me the first 200 items.
How can I remove the cell altogther if the data==null example
NSUrl nsUrl = new NSUrl(cell.imageUrl);
NSData data = NSData.FromUrl(nsUrl);
if (data != null) {
InvokeOnMainThread (() => {
cell.imgImage = new UIImage (data);
//cell.imgImage.SizeToFit();
});
} else {
//I tried the below line but it does't work, I have a cell.index property that I set in the getCell method
_data.RemoveAt(cell.Index);//_data is the list of items that are binded to the uitableview
InvokeOnMainThread (() => {
//cell.Hidden = true;
});
}

Answer 1

You remove cells by removing them from your source and then you let UITableView know that the source has changed by calling ReloadData(). This will trigger the refresh process. UITableView will ask your source how many rows there are and because you removed one row from your data, the cell representing that row will be gone.
However ReloadData() will reload your entire table. There is a methods which allows you to remove cells specifically, named DeleteRows(). You can find an example here at Xamarin.
When deleting rows it is important that you update your model first, then update the UI.
Alternatively, I recommend you to check out MonoTouch.Dialog which allows interaction with UITableView in a more direct way. It also includes support for lazy loading images.