ICommandBars exception - ArcMap crash

[AlbertoLaurenti]

Testing my VB.NET 2010 app in ArcMap an exception occurs when ICommandBars is instantiated.

  

 ' zoom to selected      Dim mxApp As ESRI.ArcGIS.Framework.IApplication     Dim numUID As UID = New ESRI.ArcGIS.esriSystem.UID     numUID.Value = "{AB073B49-DE5E-11D1-AA80-00C04FA37860}"     Dim commandBars As ICommandBars = mxApp.Document.CommandBars   '>>> error here!!!!!!!!     Dim cmdItem As ICommandItem = CommandBars.Find(numUID, False, False)     If Not (cmdItem Is Nothing) Then         cmdItem.Execute()     End If

Message: Exception first-chance type 'System.NullReferenceException' in LUCAS.dll.

Please can anybody help me?
Thanks in advance.
AL

P.S. ArcGIS 10 SP1 on Windows 7, VS2010.

[sapnas]

Where is the initialization for mxApp? I see the declaration but no initialization.

Are you using Arcmap?

[AlbertoLaurenti]

Yes, I use ArcMap.

Dim mxDocument As ESRI.ArcGIS.ArcMapUI.IMxDocument = My.ArcMap.Application.Document

I've to "hook" ArcMap? Please could you explain me better?
Thanks

[sapnas · Accepted solution]

assign mxDocument to mxApp Prior to Dim commandBars As ICommandBars = mxApp.Document.CommandBars Statement.

[AlbertoLaurenti]

Thanks! Now it works.