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Embedding a form into another TWinControl is not difficult and allows us to create flexible GUIs without using TPageControl and Frames. For the end user, this multi-tabbed GUI is probably more familiar because all modern browsers use it, and your user may already know how to use a browser with different pages or screens open. From a developer's point of view, the multi-tabbed interface allows for much better programming patterns and practices. This technique can also be used for other scenarios where you have to embed one screen into another.

More flexible (and complex) solutions can be done involving the use of Observers, but in simple cases, this recipe's solution, based on Windows Messaging, is enough.

More information about the Observer design pattern can be found at http://sourcemaking.com/design_patterns/observer/delphi.

Other interesting solutions that don't rely on Windows Messaging and so are also cross-platform include the following:

• Solultions based on the System.Messaging.TMessageManager class. More information about TMessageManager can be obtained at http://docwiki.embarcadero.com/Libraries/en/System.Messaging.TMessageManager.
• Delphi Event Bus (DEB) is a publish/subscribe Event Bus framework for the Delphi platform. More information can be found at https://github.com/spinettaro/delphi-event-bus or you can take a look at Chapter 5, The Thousand Faces of Multithreading, in the Communication made easy with Delphi Event Bus recipe.

Code in this recipe can be used with every component that uses TStringList to show items (TListBox, TComboBox, and so on) and can be adapted easily for other scenarios.

In the recipe code, you'll also find a nice way to show status messages generated by the embedded forms and a centralized way to show application hints in the status bar.