QHashIterator 类

template <typename Key, typename T> class QHashIterator

QHashIterator 类提供 Java 样式常量迭代为 QHash and QMultiHash . 更多...

头：	#include <QHashIterator>
qmake:	QT += core

公共函数

	QHashIterator (const QHash<Key, T> & hash )
QHashIterator<Key, T> &	operator= (const QHash<Key, T> & container )
bool	findNext (const T & value )
bool	hasNext () const
const Key &	key () const
QHashIterator::Item	next ()
QHashIterator::Item	peekNext () const
void	toBack ()
void	toFront ()
const T &	value () const

详细描述

QHash 同时拥有 Java 风格迭代器 and STL 样式迭代器 . The Java-style iterators are more high-level and easier to use than the STL-style iterators; on the other hand, they are slightly less efficient.

QHashIterator<Key, T> allows you to iterate over a QHash (or a QMultiHash ). If you want to modify the hash as you iterate over it, use QMutableHashIterator 代替。

The QHashIterator constructor takes a QHash as argument. After construction, the iterator is located at the very beginning of the hash (before the first item). Here's how to iterate over all the elements sequentially:

QHash<int, QWidget *> hash;
...
QHashIterator<int, QWidget *> i(hash);
while (i.hasNext()) {
    i.next();
    qDebug() << i.key() << ": " << i.value();
}

The next () function returns the next item in the hash and advances the iterator. The key () 和 value () functions return the key and value of the last item that was jumped over.

Unlike STL-style iterators, Java-style iterators point between items rather than directly at items. The first call to next () advances the iterator to the position between the first and second item, and returns the first item; the second call to next () advances the iterator to the position between the second and third item; and so on.

If you want to find all occurrences of a particular value, use findNext () in a loop. For example:

QHashIterator<int, QWidget *> i(hash);
while (i.findNext(widget)) {
    qDebug() << "Found widget " << widget << " under key "
             << i.key();
}

Multiple iterators can be used on the same hash. If the hash is modified while a QHashIterator is active, the QHashIterator will continue iterating over the original hash, ignoring the modified copy.

另请参阅 QMutableHashIterator and QHash::const_iterator .

成员函数文档编制

bool QHashIterator:: findNext (const T & value )

搜索 value starting from the current iterator position forward. Returns true if a (key, value) pair with value value is found; otherwise returns false .

After the call, if value was found, the iterator is positioned just after the matching item; otherwise, the iterator is positioned at the back of the container.

const Key &QHashIterator:: key () const

Returns the key of the last item that was jumped over using one of the traversal functions ( next (), findNext ()).

另请参阅 value ().

bool QHashIterator:: hasNext () const

返回 true if there is at least one item ahead of the iterator, i.e. the iterator is not at the back of the container; otherwise returns false .

另请参阅 next ().

void QHashIterator:: toBack ()

Moves the iterator to the back of the container (after the last item).

另请参阅 toFront ().

void QHashIterator:: toFront ()

Moves the iterator to the front of the container (before the first item).

另请参阅 toBack () 和 next ().

QHashIterator < Key , T > &QHashIterator:: operator= (const QHash < Key , T > & container )

Makes the iterator operate on hash . The iterator is set to be at the front of the hash (before the first item).

另请参阅 toFront () 和 toBack ().

QHashIterator:: QHashIterator (const QHash < Key , T > & hash )

构造迭代器为遍历 hash . The iterator is set to be at the front of the hash (before the first item).

另请参阅 operator= ().

QHashIterator::Item QHashIterator:: next ()

Returns the next item and advances the iterator by one position.

调用 key () on the return value to obtain the item's key, and value () to obtain the value.

Calling this function on an iterator located at the back of the container leads to undefined results.

另请参阅 hasNext () 和 peekNext ().

QHashIterator::Item QHashIterator:: peekNext () const

Returns the next item without moving the iterator.

调用 key () on the return value to obtain the item's key, and value () to obtain the value.

Calling this function on an iterator located at the back of the container leads to undefined results.

另请参阅 hasNext () 和 next ().

const T &QHashIterator:: value () const

Returns the value of the last item that was jumped over using one of the traversal functions ( next (), findNext ()).

另请参阅 key ().