Wpf propertychanged handler is null

Answered by:. Archived Forums. Sign in to vote. Thursday, October 30, PM. In that ideal world, the bookkeeping code goes away and you are left with just the business logic, as shown in Listing 2. This ideal code really works-if you use Update Controls. Update Controls is an open source software library that does not require you to implement the INotifyPropertyChanged interface or fire PropertyChanged events. You just need to write your business logic. The Update Controls library figures out when your properties change and automatically updates the view.

Your WPF view will be updated whenever the property changes. For example:. MailMerge is an example of a dependent property because it depends upon other properties for its value. CurrentCustomer and Name , on the other hand, are independent properties since they can change independently. Independent properties support both read and write, but dependent properties are read-only. But writing an independent property takes one additional step. You need to create an Independent sentry object that keeps track of every get and set.

Listing 3 shows the CurrentCustomer property as an example. Creating these sentries is all you need to do, but you need to do it for every independent property. Whereas INotifyPropertyChanged forces you to write bookkeeping code for intermediate logic, Update Controls makes it trivial.

In either case, the goal is separation of concerns. The pattern separates the data model from the view by interjecting an intermediate model created specifically for presentation. This intermediate presentation model transforms the data model into a form that the view can easily consume. The presentation model is an adapter between the data model and the view. See Figure 1 for a diagram of the resulting structure.

Why is this important? The data model is concerned with storing data. It should be a faithful representation of the problem domain. It should be useful not only to the UI, but also to business logic. It should not have any presentation logic-you should delegate presentation logic to the presentation model. It is an adapter between the Customer data model and the view.

But the view also needs direct access to the data model for its other behavior. Now the view has access to the data model. I also have seen the PropertyChanged event be null when I have existing data assigned to the control's data bound property:.

Ensure the property name passed in as an argument when raising the event actually matches the name of the property you are targeting. Ensure that you are using only one instance of the object that contains the property you are binding to. For item number two, this can be done by simply placing a break point on the class constructor for the object that harbors the property that is being bound. If the breakpoint is triggered more than once, then you have a problem and need to resolve the number of instances of objects to only one instance that your runtime invokes via XAML.

Thus, it's better to implement that class as a singleton pattern so that you can ensure just one instance of the object at runt-time. I had a similar issue, neither solutions above helped me. All I needed to do was to use the built c P ropertychanged. Beforehand I have implemented propertyChanged by an accident and it pointed at nothing.

If you follow all instructions, verifying your property name is correct, that it is correctly being assigned a new value, you are using a singleton to guarantee one instance of you view model, and you have successfully assigned your DataContext in the UI - make sure that whatever is forcing your property to update is done after the visual tree has been completed, i. I say this because I had the same issue, and found that when I refreshed my view model data property from my Infragistics NetAdvantage ribbon window's Loaded event, my PropertyChanged event was always null.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. PropertyChanged event always null Ask Question. Asked 12 years, 3 months ago. Active 1 year, 9 months ago. Viewed 68k times. GetInstance ; testMessage. Improve this question. Property Changed Event Reference Is this page helpful? Please rate your experience Yes No.

Any additional feedback? Namespace: System. ComponentModel Assembly: System.