Class KTrader

A Trader interface, similar to the CORBA Trader. Basically, it provides a way for an application to query all KDE services (that is, applications and components) that match a specific set of requirements. This allows you to find an application in real-time without you having to hard-code the name and/or path of the application. It is mostly used when you want to do complex queries that KServiceTypeProfile can't handle. \par Examples A few examples will make this a lot more clear. Say you have an application that will display HTML. In this example, you don't want to link to khtml... and furthermore, you really don't care if the HTML browser is ours or not, as long as it works. The way that you formulate your query as well as the way that you execute the browser depends on whether or not you want the browser to run stand-alone or embedded. If you want the browser to run standalone, then you will limit the query to search for all services that handle 'text/html' and, furthermore, they must be applications (Type=Application). You then will use KRun.run() to invoke the application. In "trader-speak", this looks like so:

 ArrayList offers = KTrader.self().query("text/html", "Type == 'Application'");
 KService.Ptr ptr = offers.first();
 KURL.List lst;
 lst.append("http://www.kde.org/index.html");
 KRun.run(ptr, lst);
 

It should be noted that in the above example, using KServiceTypeProfile would be the better choice since you would probably want the preferred service and the trader doesn't take this into account. The trader does allow you to do more complex things, though. Say, for instance, you want to only choose Netscape. You can do it with the constraint: "(Type == 'Application') and (Name == 'Netscape')" More the likely, though, you will only use the trader for such things as finding components. In our continuing example, we say that we want to load any KParts component that can handle HTML. We will need to use the KLibFactory and KLibLoader to actually do something with our query, then. Our code would look like so:

 ArrayList offers = KTrader.self().query("text/html", "'KParts/ReadOnlyPart' in ServiceTypes");
 KService.Ptr ptr = offers.first();
 KLibFactory factory = KLibLoader.self().factory( ptr.library() );
 if (factory)
   part = static_cast(factory.create(this, ptr.name(), "KParts.ReadOnlyPart"));
 

Please note that when including property names containing arithmetic operators like - or +, then you have to put brackets around the property name, in order to correctly separate arithmetic operations from the name. So for example a constraint expression like X-KDE-Blah < 4 needs to be written as [X-KDE-Blah] < 4 otherwise it could also be interpreted as Substract the numeric value of the property "KDE" and "Blah" from the property "X" and make sure it is less than 4. Instead of the other meaning, make sure that the numeric value of "X-KDE-Blah" is less than 4. See also the formal syntax defined in KTrader .

Author: Torben Weis

UNKNOWN: Provides a way to query the KDE infrastructure for specific applications or components.

		 (Type == 'Service') and (('KParts/ReadOnlyPart' in ServiceTypes) or (exist Exec))