Sunday, December 28, 2014

WPF binding system queries VM upon PropertyChanged event

-- http://msdn.microsoft.com/en-us/magazine/dd419663.aspx pointed out ...

The INotifyPropertyChanged interface contains an event pseudo-field called PropertyChanged.

Whenever a property on a ViewModel object (or a Model object) has a new value, it can (should?) raise the PropertyChanged event to notify the WPF binding system. Upon receiving that notification, the binding system queries the property, and the bound property on some UI element receives the new value. I believe this is how new data hits the screen.

I believe the callbacks run on the UI thread, just like swing.

In order for WPF to know which property on the ViewModel object has changed, the PropertyChangedEventArgs class exposes a PropertyName property of type String. You must be careful to pass the correct property name into that event argument; otherwise, WPF will end up querying the wrong property for a new value.

For PropertyChanged to work, i think we have to use xaml binding with a prop name. In contrast, the alternative -- defining ItemSource in codebehind probably doesn't work. 

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