keyfreq | Logs all key presses with a timestamp | Frontend Framework library

A key point to be aware of when using binding is that the control doesn't get updated from bound properties unless and until it's notified that the values have changed. There are two basic ways to implement this notification:

1. Inherit your ViewModel from INotifyPropertyChanged and invoke the PropertyChanged event whenever your property value changes. This approach is suitable for most situations, including numerical and string properties bound to controls such as TextBlock and TextBox.

2. Use ObservableCollection for collections bound to the ItemsSource property (for controls which have an ItemsSource property).

Controls are aware of the INotifyPropertyChanged interface and the INotifyCollectionChanged interface underlying ObservableCollection, and listen for the appropriate PropertyChanged and CollectionChanged events.

Guidelines for selecting the appropriate technique are as follows:

• If the property value in the ViewModel is set before the control's DataContext has been set to the ViewModel and never subsequently changes, you actually don't need to use the PropertyChanged notification at all, because the control will see the intended property value when the ViewModel is bound.
• If you are binding to a property for which the value will be intially assigned or will change after the DataContext has been set to the ViewModel, the ViewModel must inherit from INotifyPropertyChanged and the property setter must invoke the PropertyChanged event, otherwise the control will never be aware that the property value has changed.
• If you are binding a collection to control's ItemsSource property, you need to consider the above, but you also need to consider how and when you are populating or updating the collection's contents.
• If you are creating and populating a collection such as a list, then setting a ViewModel's property (which is bound to a control's ItemsSource property) and never modifying the collection's contents (although you may later assign the ViewModel property to different collection), the ViewModel must inherit from INotifyPropertyChanged and the collection property setter must invoke the PropertyChanged event. In this scenario, you actually don't need to consider ObservableCollection; you can use any desired collection type in your ViewModel.
• If you are modifying your collection's contents while it is bound to a control's ItemsSource property, CollectionChanged events are required for the control to update correctly; the easiest way to accomplish this is to use an ObservableCollection in your ViewModel; it will automatically raise CollectionChanged events as items are added or removed.

These are basic guidelines that should help to identify and resolve the most common/most likely problems when using binding.

Typical property binding: