http://doc.qt.nokia.com/4.7-snapshot/qml-repeater.html#details
The Repeater element creates all of its delegate items when the repeater is first created.This can be inefficient if there are a large number of delegate items and not all of the items are required to be visible at the same time. If this is the case, consider using other view elements like ListView (which only creates delegate items when they are scrolled into view) or use the Dynamic Object Creation methods to create items as they are required.
一开始就创建所有的delegate items 。数量很多时候没有效率。可以用ListView或者是Dynamic Object Creation