Using KTextTemplate in your application

Using KTextTemplate in Qt applications will often not require much code.

auto engine = getEngine();
auto t = engine->loadByName( "mytemplate.html" );
Context c;
c.insert( "some_input", some_value );
browser.setHtml( t->render( c ) );

Error handling etc is omitted for clarity. In order for the above to work as expected, it is necessary to configure the build system to find KTextTemplate, and to configure KTextTemplate to find templates and plugins.

Finding KTextTemplate with CMake

KTextTemplate uses the CMake cross platform build system, and installs a cmake file called KF6TextTemplateConfig.cmake. This config file is automatically searched for by CMake and contains the information needed for other CMake based applications to find headers and link against KTextTemplate libraries. See https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html for more.

When creating an application using CMake that depends on KTextTemplate, first issue the find_package command, and then use the CMake target_link_libraries command link to and use the libraries.

cmake_minimum_required(VERSION 2.8.11)
find_package(KF6TextTemplate REQUIRED)
# ... Application sources etc.

Deploying Templates

Template files can be installed by your application and must later be found by KTextTemplate so they can be used. If the files are installed on the filesystem, the path they were installed to can be specified when creating a AbstractTemplateLoader instance.

Engine* getEngine()
auto engine = new Engine( this );
loader->setTemplateDirs( QStringList{ path_to_installed_templates } );
engine->addTemplateLoader( loader );
return engine;
QSharedPointer< T > create(Args &&... args)

It is also possible to compile the templates into a Qt Resource file and set the resource URL on the AbstractTemplateLoader instance.


<!DOCTYPE RCC><RCC version="1.0">

CMake code:

set (_rcc_file "my_app_templates.qrc")
qt5_add_resources(_template_rcc_src ${_rcc_file} OPTIONS -root "/templates/" )
add_executable(my_app, ${my_app_srcs} ${_template_rcc_src})

Application code:

loader->setTemplateDirs( QStringList{ ":/templates/" } );
engine->addTemplateLoader( loader );

The -root option passed to rcc in CMake causes the templates to be in the virtual filesystem location ":/templates/mytemplate.html" etc. This name spacing helps keep independent data in the virtual filesystem separate.

Finding user defined templates

If users are able to define their own templates in an application that uses KTextTemplate for theming for example, the path to the location of such potential templates must also be set through the AbstractTemplateLoader instance. Paths to user defined templates should be defined before default/installed templates so that the user templates are found first. If there is a reason to disallow user overriding of certain templates, they can be specified in a separate AbstractTemplateLoader instance.

QStringList{ path_to_non_overridable_templates }
engine->addTemplateLoader( no_override_loader );
QStringList{ path_to_user_templates, path_to_default_templates }
engine->addTemplateLoader( override_loader );

Additionally, the External binary resources feature could be used to allow savvy users to share themes/templates in a package, or to deploy updated templates easily to existing deployed applications.

Finding tags and filters

KTextTemplate looks for plugins in the paths from the Engine::pluginPaths property. It does so in the same order they appear there.

The property defaults to the following directories

  • The default plugin directory of your Qt installation (qmake -query QT_INSTALL_PLUGINS).
  • The directories specified in the environment variable QT_PLUGIN_DIR.
  • The default plugin directory of your KTextTemplate installation.

Each path has "kf6/ktexttemplate" appended to it, and the resulting directory is searched for plugins. For example, if QCoreApplication::libraryPaths() contains "/usr/lib/plugins/", the directory "/usr/lib/plugins/kf6/ktexttemplate" would be searched for plugins. The search stops when a plugin matching a particular name is found.

The paths used to search for plugins can be overriden by using Engine::setPluginPaths. If you just want to add some additional paths use Engine::addPluginPath. The added path will be prepended to the list of search paths.

Deploying custom tags and filters

Custom tags and filters can be defined in C++ code or in Javascript.

To create a custom C++ plugin it must be built as part of a library and installed in a location known to the application.

# CMake code
add_library(my_custom_plugin MODULE
install(TARGETS my_custom_plugin

In this case, my_custom_plugin is a name used for the plugin in the CMake environment. It is used to install the custom library in the CMake install command.

custom_plugin_library.cpp is the C++ file where you implement the KTextTemplate::TagLibraryInterface to return custom tags and filters.

Note that the PLUGIN_INSTALL_DIR given to the install command should point to the subdir specific for the KTextTemplate plugins. For example, /usr/share/my_app/plugins/kf6/ktexttemplate/.

In C++ code, it is necessary to either instruct the KTextTemplate::Engine about the location of the plugins or to configure your QCoreApplication::libraryPaths by another standard method. Note that it is possible to define custom versions of built in tags and filters by putting your own plugin library in the path before the path to the default KTextTemplate plugins.

For example, if your custom plugin library contained a custom implementation of the {% for %} tag:

auto engine = new Engine( this );
QStringList{ path_to_custom_plugins, path_to_ktexttemplate_defaults }

Custom tags and filters implemented in Javascript can also be deployed on the file system, or, like template files, can also be deployed in Qt Resource files. In that case, the plugin subdir should be specified in the -root argument in CMake.

# CMake code:
set (_rcc_file "my_qtscript_library.qrc")
OPTIONS -root "/plugins/kf6/ktexttemplate"
add_executable(my_app, ${my_app_srcs} ${_scripted_rcc_src})
# C++ code:
engine->setPluginPaths( QStringList{ ":/plugins/" } );

Note again that when specifying the path in the virtual filesystem, the subdir is omitted. User defined filter written in Javascript can also be located similiarly to templates from either the filesystem or the Qt Resource virtual filesystem.

Building KTextTemplate

It is possible to build only parts of KTextTemplate if your application is a QCoreApplication that depends only on QtCore

The appropriate options may be specified in the cmake gui, or on the command line using the BUILD_TEXTDOCUMENT or BUILD_TEMPLATES CMake options.

mkdir build && cd build

Similarly, it is possible to build only the core of the KTextTemplate Template library without the plugins. This may be useful for specialized applications, but as the unit tests depend on the plugins, the tests would need to be deactivated in this case too:

mkdir build && cd build

By default, KTextTemplate depends on the QtQml library in order to implement Javascript support. This support is only enabled if the QtQml library is found.

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