You are developing a Windows Presentation Foundation (WPF) application. You build a dictionary that implements INotifyPropertyChanged. You want to use an indexer to bind to the UI. The…

You are developing a Windows Presentation Foundation (WPF) application. You build a dictionary that implements INotifyPropertyChanged. You want to use an indexer to bind to the UI. The relevantimplementation of the dictionary is as follows. (Line numbers are included for reference only.) You need to ensure that the PropertyChanged event is triggered so that the UI is updated if you modify the collection using theindexer. Which code should you insert at line 17?