The "multimodal user interface" is a commonplace. First of all, you need to clearly understand what is that:
http://en.wikipedia.org/wiki/Multimodal_interaction[
^].
As you can see, there is nothing specific to a particular UI framework or library you would use, but implementation will be different. Unfortunately, you did not even tag your application type. There are too many different architectures to cover them all in this aspect: WPF, Forms, Silverlight, ASP.NET, Metro, different architectural frameworks on the of those (such as MVC, MVVM), and a lot more. So, sorry, no technical detail.
Perhaps, the only common point for all the solution is this: you will have to define the data type describing mode, perhaps some "Mode Manager", because, for example, you may decide to have one global mode for the whole application, but to keep more then one non-modal view at the same time. In this case, if you change the mode in one view, you will need to notify other views. Even if you have only one view, you might have other reasons for "mode management".
—SA
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