Hello,
I've created a basic web part page using windows authentication in Visual Studio 2010 Express, and also Visual Studio 2012 Express.
I have a custom dropdown control that is populated by code validates if every display mode in the WebPartManager is enabled, and then proceeds to add that to the dropdown control. 
"mode.IsEnabled(_manager)"
This is taken from the microsoft example: http://msdn.microsoft.com/en-us/library/sk23dydw(v=vs.100).aspx
foreach (WebPartDisplayMode mode in _manager.SupportedDisplayModes) { String modeName = mode.Name; if (mode.IsEnabled(_manager)) { ListItem item = new ListItem(modeName, modeName); DropDownListModes.Items.Add(item); } }  
In Visual Studio ...

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