Development/Architecture/KDE4/XMLGUI Technology

 

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Note
I don't really feel overly qualified to write this page, but I've spent a whole lot of time figuring out some of the following things for lack of good documentation. So I'll make a start... --Tfry 14:02, 22 May 2009 (UTC)

Related information resources

• KAction tutorial
• Documentation for KDE 3 (still mostly valid)
• KParts - perhaps the most important use case for advanced KXMLGUI stuff
• kpartgui / KXMLGUI document type definition
• API documentation on KXMLGUI classes
  • KXMLGUIClient - The base class for components that use and xml-gui
  • KXMLGUIFactory - The class responsible for managing one or many KXMLGUIClients in an application.
  • KXMLGUIBuilder

Basics

For basic information, please start reading at Development/Tutorials/Using_KActions. For most simple cases you should be able to write a ui.rc for your application by simply expanding on the given examples.

Merging several KXMLGUI definitions

Once you have more than a single KXMLGUIClient/KPart in an application, it becomes important to control just how / just where menu entries and toolbar icons are merged.

How does merging happen

The first thing that happens is that the ui.rc file of you application is merged in the KDE global ui_standards.rc-file. This is to make sure that standard elements all end up in the KDE standard places.

Now, when you add further KXMLGUIClients (e.g. a KPart, or a plugin), in general the KXMLGUIFactory does the following:

• So called containers ("Menu", "ToolBar") are matched by their name. So if your application_ui.rc defines a menu with name="my_stuff", and the plugin_ui.rc of a plugin also has a menu by that name, the elements from that menu in the plugin get added to the elements of that menu in the application.
• All entries within a container are appended at the end, in the order they get added. This means, if you add KXMLGUIClient A after KXMLGUIClient B, the actions from A will generally end up after the actions from B, and vice versa.

Of course KXMLGUI allows for sophisticated ways to control this merging, and we'll deal with those in a minute, but first let us look at this basic scenario:

Bringing the clients together in C++: MyMainWindow::MyMainWindow (...) : ... { [...]

 setXMLFile ("main_ui.rc");
 insertChildClient (new MyComponentA ());
 insertChildClient (new MyComponentB ());

[...] }

MyComponentA () : public KXMLGUIClient () { [...]

 setXMLFile ("component_a.rc");

[...] }

MyComponentB () : public KXMLGUIClient () { [...]

 setXMLFile ("component_b.rc");

[...] }

main_ui.rc <?xml version="1.0" encoding="UTF-8"?> <gui [...]>

 <MenuBar>
   <Menu name="menu1" >
     <Action name="main_first" />
     <Action name="main_second" />
     <Action name="main_third" />
   </Menu>
   <Menu name="menu2" >
   </Menu>
 </MenuBar>

</gui>

component_a.rc <?xml version="1.0" encoding="UTF-8"?> <gui [...]>

 <MenuBar>
   <Menu name="menu1" >
     <Action name="a_first" />
   </Menu>
   <Menu name="menu3" >
     <Action name="a_second" />
   </Menu>
   <Menu name="menu2" >
     <Action name="a_third" />
   </Menu>
 </MenuBar>

</gui>

component_b.rc <?xml version="1.0" encoding="UTF-8"?> <gui [...]>

 <MenuBar>
   <Menu name="menu3" >
     <Action name="b_first" />
   </Menu>
   <Menu name="menu2" >
     <Action name="b_second" />
   </Menu>
   <Menu name="menu1" >
     <Action name="b_third" />
   </Menu>
 </MenuBar>

</gui>

Now all of these together would look like this:

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Note
The XML-files are not really merged together in this way. But this is an easy way to show the effect of the combination of these KXMLGUIClients.

<?xml version="1.0" encoding="UTF-8"?> <gui [...]>

 <MenuBar>
   <Menu name="menu1" >
     <Action name="main_first" />
     <Action name="main_second" />
     <Action name="main_third" />
     <Action name="a_first" />
     <Action name="b_third" />
   </Menu>
   <Menu name="menu2" >
     <Action name="a_third" />
     <Action name="b_second" />
   </Menu>
   <Menu name="menu3" >
     <Action name="a_second" />
     <Action name="b_first" />
   </Menu>
 </MenuBar>

</gui>

Things to note:

• Actions from component_a.rc are placed below actions from main_ui.rc, because MyComponentA gets added after MyMainWindow. Similarily, actions from component_b.rc are placed below those from main_ui.rc and component_a.rc.
• When component_a.rc is read, a menu named "menu2" already exist, and is therefore merged with the existing one. Due to this, "menu3" gets appended at the end of the menubar, instead of between "menu1" and "menu2". Similarily the order of the definition of the menus in component_b.rc is effectively ignored, because those menus have already been defined, previously.

Elements to control merging

Often times the above principles of merging are not good enough. Fortunately, there are several ways to control the details of merging.

MergeLocal / Merge

MergeLocal

This is only to be used in the global ui_standards.rc-file. Defines points where other entries can be merged in.

Limitations of merging and workarounds

merging of grand-children

(e.g. a plugin inside a part inside a main window)

stripping down a KPart's GUI

(hack to (re-)move unwanted elements)