title: How to Access Data between ViewModels?
body: <p>I'm currently working on a project, and for the sake of simplifying explanations, let's say that there are two tabs in a TabControl...</p>
  
  <p>In one tab, you add folders to a ListBox.</p>
  
  <p>In the other tab, there is a ListBox that displays all of the items in all of the folders you have added.</p>
  
  <p>Each tab is a ViewModel (this is to simplify code, as dumping all the code in one ViewModel makes it hard to read and understand).</p>
  
  <p>In order for this program to work, both ViewModels need to access the list of items: one because it has to display them, and the other because it has to add to them.</p>
  
  <p>I am having trouble figuring how to do this. I initially thought that sharing data is bad and this shouldn't have occurred in the first place, but then I realised that I can't think of any other way to do this.</p>
  
  <p>I am new to MVVM (this is my first real application using MVVM) and initally started using it, as I couldn't access data between classes, and thought MVVM would somehow sort this issue, but here I am again.</p>
  
  <p>I would appreciate it if someone can tell me how I could do this, and potentially explain it with example code. I am also open to suggestions and constructive criticism to my methods.</p>