move_next()

template<typename type_t >

virtual bool xtd::collections::generic::ienumerator< type_t >::move_next ( )

pure virtual

Advances the enumerator to the next element of the collection.

Returns

true if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.

Exceptions

xtd::invalid_operation_exception

The collection was modified after the enumerator was created.

Examples

The following code example demonstrates the implementation of the IEnumerator interfaces for a custom collection. In this example, xtd::collections::generic::ienumerator::move_next is not explicitly called, but it is implemented to support the use of foreach (for each in Visual Basic). This code example is part of a larger example for the IEnumerator interface.

// When you implement IEnumerable, you must also implement IEnumerator.
class people_enum : public ienumerator<person> {
private:
  // Enumerators are positioned before the first element
  // until the first move_next() call.
  size position_ = box_integer<size>::max_value;
 
public:
  const list<person>& people;
 
  explicit people_enum(const list<person>& people) : people {people} {}
 
  bool move_next() override {
    ++position_;
    return position < people.count();
  }
 
  void reset() override {position_ = box_integer<size>::max_value;}
 
  const person& current() const override {
    try {
      return people[position_];
    } catch (const index_out_of_range_exception& e) {
      throw invalid_operation_exception {csf_};
    }
  }
};

Remarks

After an enumerator is created or after the xtd::collections::generic::ienumerator::reset method is called, an enumerator is positioned before the first element of the collection, and the first call to the xtd::collections::generic::ienumerator::move_next method moves the enumerator over the first element of the collection.

If xtd::collections::generic::ienumerator::move_next passes the end of the collection, the enumerator is positioned after the last element in the collection and xtd::collections::generic::ienumerator::move_next returns false. When the enumerator is at this position, subsequent calls to xtd::collections::generic::ienumerator::move_next also return false until xtd::collections::generic::ienumerator::reset is called.

If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of xtd::collections::generic::ienumerator::move_next is undefined.

Implemented in xtd::collections::generic::enumerator< type_t >.