Lazarus Examples Window

This wiki page now a reference for the new Example Window that exists, at present, in lazarus-main but not a release version. Its based on this forum thread - https://forum.lazarus.freepascal.org/index.php/topic,57680.0.html and is by no means finalized.

For the end user

An end user gets to the Example Window after clicking the button on the Project Wizard screen or from the Tools Menu, "Example Projects". In either case they see a window offering a list of known examples. The list can be filtered by key words or by category (double click between category checkboxes turns all off).

The Example Window will allow the user to open, build (and edit) and run any example but note some have specific package requirements. Lazarus Source examples can be refreshed if necessary.

When opened, the examples from the Lazarus Source code are copied to a (user writable) area in the Lazarus Config directory (PCP) because, on some systems Lazarus Source is in read-only disk space. Further, this permits easy refresh of an example of the user makes changes.

Examples in the Lazarus Source

You can add an example anywhere you like in the Lazarus Source Tree, there are lots under ~/examples but also many associated with different Lazarus sub system. A few rules apply -

• The Example Name must be unique within Lazarus (when lowercased).
• The example should be self contained within its own directory. That directory (and any sub directories) will be copied to the work area so don't assume particular files are "just up one dir".
• The example should have an Example Metadata File, with a file name that corresponds to the project name and an extension of .ex-meta. The content of this file is JSON and must have a name, a category and should have a (multiline) description and keywords. See below.

If you add a new example (or remove one) to the Lazarus Source Tree, the file ~/examples/examples.txt needs to be refreshed. Its plain text, edit it directly or generate a new one with this command (on a *nix )-

$> find . -name "*.ex-meta" > examples/examples.txt

Examples in Third Party Packages

Again, you are free to place your package examples directory where you like but in order for the Lazarus Examples Window to find it, some things must be provided, note, different rules than above !

• The package must be currently installed in Lazarus (check ? see if its listed in [PCP]/staticpackages.inc)
• Your example should be in a directory of its own. You should not put more than one example in the same directory.
• In the case of Package Examples, the example directory is not moved to a work area so it can (but perhaps should not) be dependent on local, relative path files.
• It must have a Metadata File, see below.
• The Package file, that is the .lpk file must have entry such as <ExamplesDirectory Value="../demo"/>, typically just below the Author item. The value is the relative path from the .lpk file to a directory containing your example or examples. eg -

[MyPackage]
    [demo]
        mypackage_demo1.ex-meta
        ....
        [demo2]
            mypackage_demo2.ex-meta
            ....
    [package]
        mypackage.lpk

(Personally, I would put demo1 in its own directory too but the above would work !)

Note that, at present, Lazarus, when making a package, does NOT create the ExamplesDirectory entry, it will, but its a work in progress. If you want to test, manually adding that entry is the way to go right now.

The Metadata File

All examples that appear in the Example Window have a json metadata file with an extension ".ex-meta" in the top level directory of the example (not the package). Without a valid metadata file, the example will not be listed in the Example Window. An individual example project file would look like this -

{ 
"Laz_Hello" : {
    "Category" : "Beginner",
    "Keywords" : ["Lazarus", "Hello World", "TButton", "TMemo"],
    "Description" : "This might be your first Lazarus project, its the traditional Hello World.  Two buttons have been dropped on the form, renamed and their captions set. A memo was then added and each button was double clicked and what they are expected to do was set."
}

In this case, the example project files would be in a subdirectory called laz_hello, same spelling but all lowercase consistent with Lazarus.

The three fields are free form text, there is no dictionary so, you are free to introduce both new Categories and new Key Words. Its desirable that we do not have too many Categories so, perhaps consider posting a message on the forum before using a new one ? At present, the following Categories are in use Beginner; General; TAChart; DBase; LazReport; Third Party.

There is a rough and ready GUI app to make, edit and importantly, validate metadata files available at https://github.com/davidbannon/ExampleMetaData .

A standalone example ?

When user opens an example project (from the Example Window) it has been copied to a work area (in the Lazarus PCP) so if the example depends on other files from the package source tree, it won't find them. So, ensure all needed files are in or under the example top level directory. Sometimes, this may lead to duplication of files in the package tree but it is necessary for several reasons, firstly, Linux users using distro versions of Lazarus have all their examples in read only diskspace, secondly, its important that we can restore an example if the user messes it up badly. So, the user playing with the original example code is discouraged (but not prevented).

Can the IDE find the example ?

This is a question not completely answered at this stage. An example project, part of an installed package, will be found if -

• It has a metadata file and
• The package has its LPK file in the package top level directory or
• The LPK file is in a lower directory and the LPK file has a valid OtherUnitsDirectory field that points to the toplevel directory (and possible down again, eg "../Other") or
• The LPK file has a valid "ExampleDirectory" field showing how far down the LPK file is (ie '../../.');

The last option, ExampleDirectory, is not yet being written into an LPK file by the IDE but is read and used if present.

Notes

The user can view the project content and, if they choose, build the project. Later, if the user users the Example Window to again open that project, they will be asked if they want to refresh it, doing so will erase any false edits they may have made.

Important to note -

• Example Projects will not be displayed in the Examples Window unless they have a valid metadata file. An error is dropped to the console if a metadata file with bad json is encountered.
• The original copy of the Example is not altered when the Example Window is used to open an Example. So, play away !
• New examples can, potentially be added via the normal Gitlab pull request system.
• Examples demonstrating aspects of third party packages are probably best added to that package rather than to Lazarus itself.

See also

• https://forum.lazarus.freepascal.org/index.php/topic,57680.0.html
• https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues/37509
• https://gitlab.com/dbannon/laz_examples - this is just a temp home.
• https://gitlab.com/dbannon/laz_examples/-/tree/main/Utility/ExScanner - a tool for manipulating Example Projects in and around the Lazarus Src Tree. Probably past its use by date. Also has a framework to 'exercise' the Lazarus Examples Window in a stand alone, easier to manage environment.
• https://github.com/davidbannon/ExampleMetaData - a very simple editor to make and validate the Example Meta Data files.
• https://gitlab.com/freepascal.org/lazarus/lazarus/-/blob/main/components/exampleswindow/uexampledata.pas the unit making decisions about your examples.

Legacy & Developer Information

• There is some consideration of moving the core Lazarus examples to an on-line repo, such as https://gitlab.com/dbannon/laz_examples . At present, the code to do so is disabled because of problems in MacOS SSL but that repo is used if you click the View Project button. Not all Lazarus and no third party examples are there.

In the event that we re-introduce the On Line Examples model, the master.ex-meta file, regenerated frequently and downloadable from the repo to be cached locally would look like this -

{ 
"LastUpDate" : "2021-10-19T11:44:41+11:00",

"Beginner/laz_hello" : {
    "Name" : "Laz_Hello",
    "Category" : "Beginner",
    "Keywords" : ["Lazarus", "Hello World", "TButton", "TMemo"],
    "Description" : "This might be your first Lazarus project, its the traditional Hello World.  Two buttons have been dropped on the form, renamed and their captions set. A memo was then added and each button was double clicked and what they are expected to do was set.",

"Components/listview" : {
    "Name" : "ListView",
    "Category" : "Components",
    "Keywords" : ["TListView", "grid", "needs work"],
    "Description" : "A project that demonstrates some of a TListView's capabilities. Not so much a \"how to use\" as an exerciser of capabilities. Note, entering an invalid column number triggers a crash."

}

Note the date in ISO format, overall, the file is still reasonably human readable. And now, of course, its easily extendable. We could add a format version but I don't consider it necessary.