public static IObservableList <T> SeparateBy <T>(this IObservableList <T> self, Func <T> separator)
{
return(self
.SelectWithState(
0,
(changes, res) =>
{
var newChanges = new List <ListChange <T> >();
var count = res;
changes(
insert: (i, item) =>
{
if (i == count) // inserting at the end
{
if (count == 0) // inserting first element: skip the separator
{
newChanges.Add(ListChange.Insert(0, item));
}
else // add separator before item
{
newChanges.Add(ListChange.Insert(i * 2 - 1, separator()));
newChanges.Add(ListChange.Insert(i * 2, item));
}
}
else // add separator after item
{
newChanges.Add(ListChange.Insert(i * 2, item));
newChanges.Add(ListChange.Insert(i * 2 + 1, separator()));
}
++count;
},
replace: (i, item) =>
{
newChanges.Add(ListChange.Replace(i * 2, item));
},
remove: i =>
{
if (i == count - 1) // removing at the end
{
if (i == 0) // removing first element: no separator to remove
{
newChanges.Add(ListChange.Remove <T>(0));
}
else // remove separator before item
{
newChanges.Add(ListChange.Remove <T>(i * 2));
newChanges.Add(ListChange.Remove <T>(i * 2 - 1));
}
}
else // remove separator after item
{
newChanges.Add(ListChange.Remove <T>(i * 2 + 1));
newChanges.Add(ListChange.Remove <T>(i * 2));
}
--count;
},
clear: () =>
{
newChanges.Add(ListChange.Clear <T>());
count = 0;
});
return SelectResult.Create(ListChange.Combine(newChanges), count);
})
.UnsafeAsObservableList());
}