CODEWITHSUNDEEP
c#.netwpfdata-bindinginotifypropertychanged
Joan Venge
Joan Venge

Reputation: 331052

How to get notified when something changes in a WPF window?

I have an ObservableCollection that's binded to a WPF ListView, and all the values appear correct. But how can I get a notification when something that has a 2-way binding changes?

Should I use INotifyPropertyChanged just like in Winforms? Or are there better practices to do these?

I saw some people suggesting using dependency properties online, but not sure if that's what should do.

Upvotes: 5

Views: 1540

Answers (4)

HCL
HCL

Reputation: 36775

If the class I want to add a property is a DependencyObject, I generally add a DependencyProperty. If the class is a POCO (plain old clr objects), then I implement INotifyPropertyChanged.

In generall, all my business objects are POCOs and therefore I use INotifyPropertyChanged. In the WPF world, I mostly use DependencyObjects (view models, custom controls, UserControls...) and therefore they are DependencyProperties. An exception are ViewModels representing items (to be used as items in an items source). In this case I think DependencyProperties are not very practical (Because Equals() and GetHashCode() of DependencyObjects are sealed and DependencyObject is thread-dependent).

If your class already is a DependencyObject, using DependencyProperties may give you some nice advantages: You don't have to back every value, a powerfull inheritance system, default-values, property changed callbacks per property, value coercion ... (I like DependencyProperties probably more than other people them like :)

Conclusion: Based on the title of your question: How to get notified when something changes in a WPF window?, my way would be to add a DependencyProperty and not a clr-property because the Window is a DependencyObject. By the way, Visual Studio has a nice Snippet to create DependencyProperties.

Upvotes: 4

SergioL
SergioL

Reputation: 4963

There are really two scenarios:

1) Notifying the UI when a piece of data changes-either in the ViewModel or a Model that is bound to some UI elements (usually due to a data binding). In this scenario you'd use INotifyPropertyChanged.

Example: you have a Person object that binds it's Name to a TextBox. Person needs to implement INotifyPropertyChanged and the appropriate code needs to be attached to the Name Property's setter.

2) Creating custom UI elements where you'd want data to be bound. In this case, you'd use custom dependency properties.

Example: you have a custom UI element that spins when a certain condition is met. So you create an IsSpinning dependency property that you can bind to your ViewModel's IsLoading property. The custom control then uses the IsSpinning property to modify its behavior.

I hope that was clear...

Upvotes: 2

Scott
Scott

Reputation: 12050

I've generally used INotifyPropertyChanged for my data objects.

DependencyProperties can only be implemented on framework elements I believe.

Edit: I take that back... DependencyProperties can only be implemented on DependencyObjects (A FrameworkElement is an example of that as it derives from UIElement which derives from Visual which derives from DependencyObject).

If you have a UserControl, you may wish to implement a Dependency Property so you can Bind that Property (in XAML) to some other property. You could not do this scenario with INotifyPropertyChanged.

Upvotes: 1

Davita
Davita

Reputation: 9124

You are right. You can use INotifyPropertyChanged or you can implement dependency properties. Personally I prefer INotifyPropertyChanged, it's more light and easyer to implement than dependency property.

Upvotes: 1

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