KReport
This section describes how to create your own item types for KReport by implementing a sample plugin that adds a filled rectangle to the report.
Base Item
The duties of the base item is to extract values of its properties, such as position or size, from the report’s XML, and to create the rendering primitives to draw from the given data.
KReport will give us the XML data in the form of a QDomNode object that only contains the fragment relevant to our item. In this case, the XML structure will be something like the following:
<report:rect report:name="rect1"
report:z-index="0"
svg:x="113.386023318759058pt"
svg:y="21.259879372267321pt"
svg:height="40.500000848363968pt"
svg:width="210.000004398924290pt"
fo:background-color="#ffffff"
fo:background-opacity="0%"
>
<report:line-style report:line-style="solid"
report:line-weight="1"
report:line-color="#000000"
/>
</report:rect>
As for the rendering primitives, there are two type of items: these that create them based on a simple value from the data source, for instance a label, and these that use a subquery to extract the data, as is the case for charts; the former need to implement KReportItemBase::renderSimpleData while the latter need KReportItemBase::renderReportData. Rendering a rectangle does not need data from a source and will be a simple item that ignores its input.
As we will see later, the default constructor will be used when creating an empty item from the designer and it must create all properties except for the name, size, position, and data source, because these are created by KReportItemBase:
As you can see, we create a KProperty object for each property that can be set and then we add them all to the item’s property set, that will manage their life cycle and signals.
The constructor accepting a QDomNode must extract the properties’ value from it. Fortunately, KReportItemBase and KReportUtils already contain functions to help us in reading common properties.
Notice how we can call nameProperty() to set this item’s name even though we did not create that property. Also, parseReportRect will read the svg:x, svg:y, svg:width and svg:height attributes from the node’s element and initialize the corresponding position and size properties that we have inherited from KReportItemBase.
Now we are ready to render rectangles to the report’s output. renderSimpleData receives the page and the section that the item needs to render to add the rendering objects to, and must return how much it stretches the section’s height, for instance as a result of wrapping text. Both are nullptr when KReport is computing the actual section’s height.
data contains the value that the item must render and is given by the data source. For a rectangle we already got all the information required from the XML and can safely ignore this parameter.
In this case we only need to create an ORORect object and set all its attributes from the item’s properties. KReportItemBase::scenePosition and KReportItemBase::sceneSize convert, respectively, the position and size from point units to pixels according to the output’s DPI.
The only remaining bit is to tell KReport the item‘s name, that will be the basis for its XML tag. That is, "<report:" + typeName() + ">".
Designer Item
The designer item extends from the base item and its duties are to build the XML node that will be placed in the report’s structure, and to draw a preview in the designer’s QGraphicsScene. This object can start its life with the properties at their default values or by initializing their values from a QDomNode, like the base item does.
KReportDesignerItemRectBase is a class that extends KReportDesignerItemBase and is used as the base class for items that are “rectangular”. This, of course, includes our rectangle, but also items such as fields and labels because they define a rectangular area where they will render its data in. Extending from this class means that we do not need to take care of handling mouse events and can easily draw the item’s resize handles when it is selected.
The constructor accepting a QDomNode is called when the designer loads an existing document and we simply call the base item’s constructor to initialize the properties from the XML node. The other constructor is called when the user creates a new item on the designer widget and we need to create a default-valuated instance; notice how we ask KReportDesigner to suggest us a name based on the item’s type name. In both cases we have to initialize this item in the scene graph and setup a slot that will inform the designer when a property has changed.
When the designer wants to write the report’s template in XML, it will call buildXML() with the XML document that is creating and the node that needs to be this item’s parent. Our job is to create the same XML structure that the base item’s constructor accepting a QDomNode can read. Again, KReportDesignerItemBase has utility functions to help us build the XML of common elements and attributes.
In fact, we can use this dynamic of buildXML() generating the XML node that the constructor can read to implement the required clone method. This method is called by KReportDesigner to copy and paste items, among others.
The last thing to do is draw the actual item on the designer. In contrast to KReportItemBase, KReportDesignerItemRectBase is a QGraphicsItem-derived class and must know how to paint itself using a QPainter. For a rectangle we only have to take the same brush and pen that we use when building a ORORect and paint a rectangle at the current position and size. KReportDesignerItemRectBase::drawHandles will render the eight small boxes all around the rectangle that allow users to resize our item with the mouse.
Scripting
KReport allows users to write scripts in JavaScript to change items’ properties. For example, the following script for a report named example_report would change the background color of an item named rect1 to the color #abc, and toggle the section’s between #ffffff and #dddddd prior to rendering it:
KReport uses QML’s QJSEngine to run JavaScript and calling objectByName from the script will try to create a QObject-derived object that wraps the item whose name is passed as parameter. This QObject needs to define Qt properties in order to provide a way to write and read item's property values. By convention, the scripting class is from the Scripting namespace.
The implementation is very straightforward and just needs to set or get the item’s property values.
Because most of KReportRectItem properties are private, we need to make Scripting::Rect a friend class by appending the following at the end of KReportRectItem’s declaration:
Implementing the Plugin Interface
We already have all the actors ready — the base item class, the designer’s, and the class that allows changing its properties from scripts —, but we need a way to somehow tell KReport that they exist. This is done by implementing the KReportPluginInterface interface.
KReportPluginInterface::createRendererInstance is called when there is the need to instantiate a base item for rendering the report. It is given the QDomNode from the report’s XML template of this item.
.
Likewise, KReportPluginInterface::createDesignerInstance is called to instantiate a designer item. As we saw above, the designer item can be needed when loading an XML document or when the user creates a new item in the designer widget, that is why there are two different signatures for this method.
The last class we need to instantiate is the QObject-derived object used in scripts. The method receives the item to wrap as a parameter. Due to the dynamic nature of JavaScript, we need to cast it to the type of our item and make sure it is correct.
The last thing required to implement this interface is to create a plugin factory. It can be done with the K_PLUGIN_CLASS_WITH_JSON macro, that expects the name of the class extending KReportPluginInterface and the name of a JSON file with valid KPlugin metadata. It is also necessary to include the source code generated by the Qt MOC in the plugin’s implementation file in order to compile the generated factory code.
The JSON file must have all necessary KPlugin metadata. Also, "Version" must be set to the major and minor component of KReport’s stable version. For example, in KReport 3.2.1 "Version" must be set to "3.2".
Lastly, the JSON file must contain a "X-KDE-PluginInfo-LegacyName" property with the exact same value as the return value of KReportItemBase::typeName or KReport would fail to find the plugin when reading XML templates or creating new items in the designer.
{
"KPlugin": {
"Authors": [
{
"Email": "[email protected]",
"Name": "Proud Author"
}
],
"Category": "",
"Description": "Rectangle element for Reports",
"Icon": "draw-rectangle",
"Id": "org.kde.kreport.rect",
"License": "LGPL",
"Name": "Rect",
"Version": "3.3"
},
"X-KDE-PluginInfo-LegacyName": "rect",
"X-KReport-PluginInfo-Priority": "100"
}
The last piece you need for a complete item plugin is a CMakeLists.txt that compiles and installs the plugin. The CMakeLists.txt looks like the following:
find_package(ECM 1.8.0 NO_MODULE REQUIRED)
set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH})
include(KDEInstallDirs)
include(KDECMakeSettings NO_POLICY_SCOPE)
include(KDEFrameworkCompilerSettings NO_POLICY_SCOPE)
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
find_package(Qt5 5.4.0 COMPONENTS Core REQUIRED)
find_package(KReport 3.2.90 NO_MODULE REQUIRED)
set(kreportrectplugin_SRCS
kreportrectdebug.cpp
kreportrectdesigneritem.cpp
kreportrectitem.cpp
kreportrectplugin.cpp
)
if (KREPORT_SCRIPTING)
list(APPEND kreportrectplugin_SRCS
kreportrectscript.cpp
)
endif(KREPORT_SCRIPTING)
add_library(KReportRectPlugin MODULE ${kreportrectplugin_SRCS})
target_link_libraries(KReportRectPlugin PRIVATE Qt5::Core KReport)
install(TARGETS KReportRectPlugin DESTINATION ${KDE_INSTALL_PLUGINDIR}/kreport3)
Now you can compile the type plugin and install it. Once done, the new plugin should be available for every application using KReport. In applications that utilize the Report Designer, Items toolbar should also offer the new item type.
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