Add Help to Your Application

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The LCL comes with a help system, and allows you to create help for your own applications.

Quick Start

Open the example in examples/helphtml/.

This project demonstrates how to use the HTML help components. Just drop them on a form of your project. Setup the paths and create some HTML pages. Then give each control of your application a HelpKeyword.

Help Basics

The LCL help mainly consists of two parts: Help databases and help viewers. A Help Database contains the mapping from the keywords (ID, node, message, pascal, ...) to the help page (or whatever). The Help Viewer is invoked by the Help Database to show the help to the user.

  • A THelpDatabase manages content. It can be a collection of html pages or fpdoc xml files or a chm file or a database or whatever.
  • A THelpViewer is a component to show help content. For example a viewer for the mime type text/html can start a webbrowser.

When help is requested the LCL queries each registered THelpDatabase and each database can return a list of entries. If several entries are returned the LCL asked the user to select one entry. Then the LCL asks the database to show the help for the entry. The database then extracts the help content and asks the LCL for an viewer that supports the mime type of the content. The viewer then shows the help content.


In Lazarus trunk as of July 2012, a demonstration program is included that shows how to include context-sensitive help using CHM and the lhelp CHM viewer (the same one that is used for IDE help by default). Please see lazarus/components/chmhelp/democontrol/. You can write your own CHM files, e.g. with the now ancient Microsoft HTML Workshop or with the new Lazarus chmmaker tools in lazarus/tools/chmmaker You can use a CHMHelpDatabase control like the HTMLHelpdatabse control described below. The advantages of using the CHM system are a smaller, self contained help file instead of multiple files. On the other hand not every system has a chm viewer, so you might want to include lhelp, a chm viewer written in pascal and included with the Lazarus sources (components/chmhelp/lhelp/lhelp.lpi).


The LCL provides two components to use html files for help: THTMLHelpDatabase and THTMLBrowserHelpViewer. To see the html help see the lazarus example examples/helphtml/htmlhelp1.lpi.

Setup html help for your application

Adding html help to your application is easy:

  • Put a THTMLHelpDatabase on a form.
  • Set AutoRegister to true.
  • Set KeywordPrefix to HTML/. It means all keywords must start with the string HTML/.
  • Set BaseURL to file://html/. This will search the html files in the sub folder html. You can specify full paths like file:///usr/lib/yourhelp/ or an URL like
  • Put a THTMLBrowserHelpViewer on the form. This component can start the default browser of the user.
  • Set AutoRegister to true.

Creating a help entry

  • Now create the sub folder html and create a html page html/edit1.html.
  • Put a TEdit on a form.
  • Set HelpType to htKeyword
  • Set HelpKeyword to HTML/edit1.html

When running the program you can focus the edit and press F1 to invoke the help. Under OS X the help key is Cmd-? (or Cmd+Shift+? depending on you keyboard layout). Note: Some window managers, widget set combinations do not pass F1 to the LCL.