How TApplication Processes VCL Help

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Go Up to Using Help in a VCL Application

The VCL Vcl.Forms.TApplication class provides four methods that are accessible from application code:

  • HelpCommand takes a Windows Help-style HELP_COMMAND and passes it off to the external help viewer application, interfaced in the package specified in the uses clause of your application. Help requests forwarded through this mechanism are passed only to implementations of ISpecialWinHelpViewer.
For Windows HTML help, you should specify the Vcl.HtmlHelpViewer unit. The Vcl.HtmlHelpViewer unit provides a Delphi interface to the HTMLHelp Windows native Help-handling function. For C++, you need to include the Vcl.HtmlHelpViewer.hpp header files. For information about the HTMLHelp or other native Help-handling functions and about the data passed to them, see the appropriate HTMLHelp topics in the MSDN Library.
  • HelpContext invokes the Help System with a request for context-based Help.
  • HelpKeyword invokes the Help System with a request for keyword-based Help.
  • HelpJump requests the display of a particular topic.

All four functions take the data passed to them and forward it through a data member of TApplication, which represents the Help system. That data member is directly accessible through the Vcl.Forms.TApplication.HelpSystem property.

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