WPF MVVM Pattern, need to send objects from one viewmodel to another one
<p>Hi I have 3 ObservableCollections of a custom type in Viewmodel lets call it ViewmodelA and I need to send those collections to ViewmodelB. I tried to register a method that returns  a List of the 3 ObservableCollections using MessengerInstance but it is complaining that it is expecting a return type of void.</p>

<p>Keeping the mvvm pattern in mind what would be the best way of getting these colllections over to ViewModelB?</p>

<p>Btw I am using mvvm-light</p>

<p>this is the method i made to return the lists:</p>

<pre><code>private List&lt;ObservableCollection&lt;Column&gt;&gt; RetrieveFilters(Column col)
{
    List&lt;ObservableCollection&lt;Column&gt;&gt; Out = new     List&lt;ObservableCollection&lt;Column&gt;&gt;
    {
        _manuColumns,
        _pnColumns,
        _nounModColumns
    };

    return Out;
}
</code></pre>

<p>then I tried to register the method with</p>

<pre><code> MessengerInstance.Register&lt;Column&gt;(this, RetrieveFilters);
</code></pre>

<p>the error I get is </p>

<blockquote>
  <p><code>List&lt;ObservableCollection&lt;Column&gt;&gt; PropertyViewModel.RetrieveFilters(Column)</code> 
  has the wrong return type   </p>
</blockquote>