QAbstractMessageHandler Class Reference
[QtXmlPatterns module]

Detailed Description

The QAbstractMessageHandler class provides a callback interface for handling messages.

QAbstractMessageHandler is an abstract base class that provides a callback interface for handling messages. For example, class QXmlQuery parses and runs an XQuery. When it detects a compile or runtime error, it generates an appropriate error message, but rather than output the message itself, it passes the message to the message() function of its QAbstractMessageHandler. See QXmlQuery::setMessageHandler().

You create a message handler by subclassing QAbstractMessageHandler and implementing handleMessage(). You then pass a pointer to an instance of your subclass to any classes that must generate messages. The messages are sent to the message handler via the message() function, which forwards them to your handleMessge(). The effect is to serialize the handling of all messages, which means your QAbstractMessageHandler subclass is thread safe.

A single instance of QAbstractMessageHandler can be called on to handle messages from multiple sources. Hence, the content of a message, which is the description parameter passed to message() and handleMessage(), must be interpreted in light of the context that required the message to be sent. That context is specified by the identifier and sourceLocation parameters to message() handleMessage().

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