After spending too many hours trying to figure this one out, I have to write it down to help any unfortunate soul that should come across this undocumented behavior. (Notice how I put all the important keywords in the title?)
While it's most often recommended to supply an IList<T>
when setting the ItemsSource
of a collection view in Xamarin.Forms or other XAML platforms, it's not required. You can just as well supply an or IEnumerable<T>
and things will work fine.
The benefit if passing a list is that the system can do random access of items. In other words, it can use the mylist[42]
syntax. This is a lot more efficient than trying to access a random item in an IEnumerable<T>
.
You might think "but there's ElementAt()
on IEnumerable<T>
". Yes, but that's basically just skipping n - 1
items before accessing the desired item. myEnumerable.ElementAt(42)
is basically this: myEnumerable.Skip(42 - 1).First()
.
In the Xamarin.Forms documentation it actually explictly tells you to provide a list if you can, for performance reasons.
Back to SfChart by Syncfusion:
Apparently there's a limitation in SfChart when it comes to IEnumerable<T>
as the ItemsSource
: If you specify a custom TrackballLabelTemplate
for your chart, it will be ignored if you don't use an IList<T>
.
This had me stuck for quite a while.
I usually provide a list when binding to ItemsSource
, but in this instance I was using Where()
in the view code-behind to filter out some unwanted items. Since Where()
returns an IEnumerable<T>
things didn't work. Putting a ToList()
after the Where()
clause fixed it all.
This wasted more hours than I want to admit to figure out...
If you stumble upon this post via Google; you're welcome :)
Happy coding!
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