QXmlResultItems Class

QXmlResultItems class iterates through the results of evaluating an XQuery in QXmlQuery . 更多...

头：	#include <QXmlResultItems>
qmake:	QT += xmlpatterns
Since:	Qt 4.4

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注意： 此类的所有函数可重入 .

公共函数

	QXmlResultItems ()
virtual	~QXmlResultItems ()
QXmlItem	current () const
bool	hasError () const
QXmlItem	next ()

详细描述

QXmlResultItems class iterates through the results of evaluating an XQuery in QXmlQuery .

QXmlResultItems presents the evaluation of an associated query as a sequence of QXmlItems . The sequence is traversed by repeatedly calling next (), which actually produces the sequence by lazy evaluation of the query.

QXmlQuery query;
query.setQuery("<e/>, 1, 'two'");
QXmlResultItems result;
if (query.isValid()) {
    query.evaluateTo(&result);
    QXmlItem item(result.next());
    while (!item.isNull()) {
        // use item
        item = result.next();
    }
    if (result.hasError()) {
        /* Runtime error! */
    }
}

An effect of letting next () produce the sequence by lazy evaluation is that a query error can occur on any call to next (). If an error occurs, both next () 和 current () will return the null QXmlItem ，和 hasError () will return true.

QXmlResultItems can be thought of as an "iterator" that traverses the sequence of query results once, in the forward direction. Each call to next () advances the iterator to the next QXmlItem in the sequence and returns it, and current () always returns the QXmlItem that next () returned the last time it was called.

注意： 当使用 QXmlResultItems overload of QXmlQuery::evaluateTo () to execute a query, it is advisable to create a new instance of this class for each new set of results rather than reusing an old instance.

另请参阅 QXmlItem::isNode (), QXmlItem::isAtomicValue ()，和 QXmlNodeModelIndex .

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QXmlResultItems:: QXmlResultItems ()

Constructs an instance of QXmlResultItems .

`[virtual]` QXmlResultItems:: ~QXmlResultItems ()

Destroys this instance of QXmlResultItems .

QXmlItem QXmlResultItems:: current () const

Returns the current item. The current item is the last item that was produced and returned by next ().

Returns a null QXmlItem if there is no associated QXmlQuery .

bool QXmlResultItems:: hasError () const

If an error occurred during evaluation of the query, true is returned.

Returns false if query evaluation has been done.

QXmlItem QXmlResultItems:: next ()

Returns the next result in the sequence produced by lazy evaluation of the associated query. When the returned QXmlItem is null, either the evaluation terminated normally without producing another result, or an error occurred. Call hasError () to determine whether the null item was caused by normal termination or by an error.