android-PagerAdapter

类概述

Base class providing the adapter to populate pages inside of a . You will most likely want to use a more specific implementation of this, such as or .

When you implement a PagerAdapter, you must override the following methods at minimum:

PagerAdapter is more general than the adapters used for . Instead of providing a View recycling mechanism directly ViewPager uses callbacks to indicate the steps taken during an update. A PagerAdapter may implement a form of View recycling if desired or use a more sophisticated method of managing page Views such as Fragment transactions where each page is represented by its own Fragment.

ViewPager associates each page with a key Object instead of working with Views directly. This key is used to track and uniquely identify a given page independent of its position in the adapter. A call to the PagerAdapter method  indicates that the contents of the ViewPager are about to change. One or more calls to  and/or  will follow, and the end of an update will be signaled by a call to. By the time  returns the views associated with the key objects returned by  should be added to the parent ViewGroup passed to these methods and the views associated with the keys passed to  should be removed. The method identifies whether a page View is associated with a given key object.

A very simple PagerAdapter may choose to use the page Views themselves as key objects, returning them from  after creation and adding them to the parent ViewGroup. A matching  implementation would remove the View from the parent ViewGroup and could be implemented as return view == object;.

PagerAdapter supports data set changes. Data set changes must occur on the main thread and must end with a call to  similar to AdapterView adapters derived from . A data set change may involve pages being added, removed, or changing position. The ViewPager will keep the current page active provided the adapter implements the method .

概述