public override View GetView(int position, View convertView, ViewGroup parent)
{
T item = this[position];
if (convertView == null)
{
convertView = CreateView.Invoke(parent);
}
var dataContextProperty = convertView.GetType().GetProperties().FirstOrDefault(i => i.Name.Equals("DataContext"));
if (dataContextProperty != null)
{
dataContextProperty.SetValue(convertView, item);
}
return(convertView);
}
public override View GetView(int position, View convertView, ViewGroup parent)
{
// The convertView is the previous View at that position (if there is one).
// So that means if something was inserted at the top, the convertView would be off by one index.
// We could theoretically assign the new data context on each one, but that means there would
// be O(N) changes to the data context of each.
// Alternatively, we can cache mappings between the item and its convertView, and return the corresponding
// view if it exists, and otherwise create and map it. That should be O(1).
// However, the convertView is also used for recycling views when scrolling through long lists...
// So theoretically, as we scroll down, the item's view at the top would end up appearing for an item further down,
// which we wouldn't return, and instead we would create a new one, and the top item's view would lose its reference.
// Best design would probably have a ViewWithDataContext, and then assign DataContext on them.
// We could also support options for keeping all views loaded.
if (CreateView == null)
{
throw new NullReferenceException("CreateView function cannot be null.");
}
var dataItem = this[position];
var cachedView = GetCachedView(dataItem);
if (cachedView != null)
{
return(cachedView);
}
var newView = CreateView.Invoke(parent, dataItem);
CacheCreatedView(dataItem, newView);
return(newView);
}
protected void InvokeCreateViewEvent(object derivedSender, ViewModelEventArgs e)
{
CreateView?.Invoke(derivedSender, e);
}
