When using collections (eg. Android.Widget.ListView, Android.Widget.StackView etc.) in widgets, it is very costly to set PendingIntents on the individual items, and is hence not permitted. Instead a single PendingIntent template can be set on the collection, see RemoteViews.SetPendingIntentTemplate(int, Android.App.PendingIntent), and the individual on-click action of a given item can be distinguished by setting a fillInIntent on that item. The fillInIntent is then combined with the PendingIntent template in order to determine the final intent which will be executed when the item is clicked. This works as follows: any fields which are left blank in the PendingIntent template, but are provided by the fillInIntent will be overwritten, and the resulting PendingIntent will be used. of the PendingIntent template will then be filled in with the associated fields that are set in fillInIntent. See Android.Content.Intent.FillIn(Android.Content.Intent, Android.Content.FillInFlags) for more details.

[Android Documentation]