c# - Getting prior value on change of property using ReactiveUI in WPF MVVM -

I am using a reactiv UI for an MVVM WPF project, and I know when a property changes

The new value (i.e. change)

I have a view modal ( Receiving from Reactive Object ) with a property declared on it:

  Personal accountholder type _accountHolderType; Public Account Holder Type Account Holder Type {Receive {Return _accountHolderType; } Set {this.RaiseAndSetIfChanged (ref _accountHolderType, value); }}  

In the manufacturer, I am trying to do the following:

  this.WhenAnyValue (vm => vm.AccountHolderType). Subscribe (Subscribe (Old, Carr) = & gt; {/} do something here));  

But there is no such surcharge in any value method, and the reactive documentation is quite lacking.

I Access a simple when any value :

  this.WhenAnyValue (vm = & Gt; vm.AccountHolderType). Subscribe (val = & gt; {// do something here}};  

This allows me to follow the changes and gets the latest changes, but I need the first price .

I know that I can implement it in simple form such as:

  public account holder type accountholder type {get {//} set {var Prev = _accountHolderType; _accountHolderType = value; // old and new values ​​work with DoSomething (formerly, value);}}  

but The project is using the reactative UI, I probably want to be in the form of "responsive-y".

< P> About:

  this.WhenAnyValue (vm = & gt; vm.AccountHolderType). Buffer (2, 1). Select (b = & gt; New {pre = Subscribe [B] [0], current = b [1]}) (t => logic by using the previous and new value for account holder type);  

I think you have forgotten this straight forward function.