Adding a tool window to an exisiting VS extension package - FindToolWindow fails

Question

I have a VS package with no tool windows, and now I want to add a first tool window to it. This is what I've done:

1. Created an empty class derived from ToolWindowPane.
2. Added Guid attribute to this class. I've generated a new GUID with the Visual Studio built-in tool.

3. Added 2 attributes to the main package class:
   [ProvideToolWindow(typeof(MainToolWindow))]
   and
   ([ProvideToolWindowVisibility(typeof(MainToolWindow), VSConstants.UICONTEXT.SolutionExists_string)]

4. Called ToolWindowPane MyWindow = this.FindToolWindow(typeof(MainToolWindow), 0, true);

This results in an exception:

Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))

What did I miss?

Answer 1

The exception was caused by content being null. Adding this to the window constructor does the trick:

Content = new System.Windows.Controls.UserControl();