title: How to deal with calculated values with Dependency Properties on a custom WPF control
body: <p>To summarize what I'm doing, I have a custom control that looks like a checked listbox and that has two dependency properties one that provides a list of available options and the other that represents a enum flag value that combines the selection options. </p>
  
  <p>So as I mentioned my custom control exposes two different DependencyProperties, one of which is a list of options called <em>Options</em> and the other property called <em>SelectedOptions</em> is of a specific Enum type that uses the [Flags] attribute to allow combinations of values to be set. My UserControl then contains an ItemsControl similar to a ListBox that is used to display the options along with a checkbox. When the check box is checked or unchecked the SelectedOptions property should be updated accordingly by using the corresponding bitwise operation. </p>
  
  <p>The problem I'm experiencing is that I have no way other than resorting to maintaining private fields and handling property change events to update my properties which just feels unatural in WPF. I have tried using ValueConverters but have run into the problem that I can't really using binding with the value converter binding so I would need to resort to hard coding my enum values as the ValueConverter parameter which is not acceptable. If anybody has seen a good example of how to do this sanely I would greatly appreciate any input.</p>
  
  <p>Side Note:
  This has been a problem I've had in the past too while trying to wrap my head around how dependency properties don't allow calculated or deferred values. Another example is when one may want to expose a property on a child control as a property on the parent. Most suggest in this case to use binding but that only works if the child controls property is a Dependency Property since placing the binding so that the target is the parent property it would be overwritten when the user of the parent control wants to set their own binding for that property.</p>