Responding to changes So far in this tutorial, we have mostly created bindings between UI elements and existing classes, but in real life applications, you will obviously be binding to your own data objects.
This is just as easy, but once you start doing it, you might discover something that disappoints you: Changes are not automatically reflected, like they were in previous examples.
As you will learn in this article, you need just a bit of extra work for this to happen, but fortunately, WPF makes this pretty easy. Responding to data source changes There are two different scenarios that you may or may not want to handle when dealing with data source changes: Changes to the list of items and changes in the bound properties in each of the data objects. How to handle them may vary, depending on what you're doing and what you're looking to accomplish, but WPF comes with two very easy solutions that you can use: The following example will show you why we need these two things: The example is pretty simple, with a User class that will keep the name of the user, a ListBox to show them in and some buttons to manipulate both the list and its contents.
The ItemsSource of the list is assigned to a quick list of a couple of users that we create in the window constructor. The problem is that none of the buttons seems to work. Let's fix that, in two easy steps.
Reflecting changes in the list data source The first step is to get the UI to respond to changes in the list source ItemsSource , like when we add or delete a user.
What we need is a list that notifies any destinations of changes to its content, and fortunately, WPF provides a type of list that will do just that. This will make the Add and Delete button work, but it won't do anything for the "Change name" button, because the change will happen on the bound data object itself and not the source list - the second step will handle that scenario though. Reflecting changes in the data objects The second step is to let our custom User class implement the INotifyPropertyChanged interface.
By doing that, our User objects are capable of alerting the UI layer of changes to its properties. This is a bit more cumbersome than just changing the list type, like we did above, but it's still one of the simplest way to accomplish these automatic updates. The final and working example With the two changes described above, we now have an example that WILL reflect changes in the data source.
It looks like this: This is the price you will have to pay if you want to bind to your own classes and have the changes reflected in the UI immediately. Obviously you only have to call NotifyPropertyChanged in the setter's of the properties that you bind to - the rest can remain the way they are.
The ObservableCollection on the other hand is very easy to deal with - it simply requires you to use this specific list type in those situations where you want changes to the source list reflected in a binding destination.