Android_ViewPager_ViewPager使用详解及相应的adapter适配器

1.ViewPager事件

ViewPager通常和Fragment配合一起使用，能够使用适当的方式去管理每一页的生命周期，并使用PagerAdapter去生成每一页显示的view数据，向左向右可以滑出每页视图。

OnPageChangeListener{/** * This method will be invoked when the current page is scrolled, either as * part of a programmatically initiated smooth scroll or a user initiated * touch scroll. *  * @param position *            Position index of the first page currently being displayed. *            Page position+1 will be visible if positionOffset is nonzero. * @param positionOffset *            Value from [0, 1) indicating the offset from the page at *            position. * @param positionOffsetPixels *            Value in pixels indicating the offset from position. */public void onPageScrolled(int position, float positionOffset,int positionOffsetPixels) {}/** * This method will be invoked when a new page becomes selected. Animation * is not necessarily complete. *  * @param position *            Position index of the new selected page. */// 一个新页被调用时执行,仍为原来的page时，该方法不被调用public void onPageSelected(int position) {for (int i = 0; i < imageViews.length; i++) {imageViews[position].setBackgroundResource(R.drawable.guide_dot_green);if (position != i) {imageViews[i].setBackgroundResource(R.drawable.guide_dot_normal);}}}/** * Called when the scroll state changes. Useful for discovering when the * user begins dragging, when the pager is automatically settling to the * current page, or when it is fully stopped/idle. *  * @param state *            The new scroll state. * @see ViewPager#SCROLL_STATE_IDLE * @see ViewPager#SCROLL_STATE_DRAGGING * @see ViewPager#SCROLL_STATE_SETTLING *//* * SCROLL_STATE_IDLE: pager处于空闲状态  * SCROLL_STATE_DRAGGING： pager处于正在拖拽中 * SCROLL_STATE_SETTLING： pager正在自动沉降，相当于松手后，pager恢复到一个完整pager的过程 */public void onPageScrollStateChanged(int state) {// System.out.println("state:" + state);}/* * { private void setScrollState(int newState) { // ... * if(mOnPageChangeListener != null) { * mOnPageChangeListener.onPageScrollStateChanged(newState);//调用 } } */}

2.PagerAdapter

//PagerAdapter是object的子类class MyAdapter extends PagerAdapter {/** * PagerAdapter管理数据大小 */@Overridepublic int getCount() {return views.size();}/** * 关联key 与 obj是否相等，即是否为同一个对象 */@Overridepublic boolean isViewFromObject(View view, Object obj) {return view == obj; // key}/** * 销毁当前page的相隔2个及2个以上的item时调用 */@Overridepublic void destroyItem(ViewGroup container, int position, Object object) {container.removeView((View) object); // 将view 类型 的object熊容器中移除,根据key}/** * 当前的page的前一页和后一页也会被调用，如果还没有调用或者已经调用了destroyItem */@Overridepublic Object instantiateItem(ViewGroup container, int position) {container.addView(views.get(position));return views.get(position); // 返回该view对象，作为key}}

3.FragmentPagerAdapter

用户访问的每页数据都保存在内存中，因此适合访问页数不是很多的情况！使用至需要复写getItem(int) and getCount()方法，如果页数很多可以使用FragmentStatePagerAdapter，通过bundle保存每页的状态信息，因而占用内存就很小。

                       

public class MainActivity extends FragmentActivity implements TabListener,OnPageChangeListener {private ActionBar actionBar;private final static int TYPE_YULE = 0;private final static int TYPE_NEWS = 1;private final static int TYPE_SPORT = 2;private static List<Fragment> fragments;private ViewPager viewPager;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);viewPager = (ViewPager) findViewById(R.id.container);actionBar = getActionBar();fragments = new ArrayList<Fragment>();fragments.add(new YuleFragment());fragments.add(new NewsFragment());fragments.add(new SportFragment());// actionBar.setBackgroundDrawable(getResources().getDrawable(R.drawable.appmgr_btn_upgrade_selected));actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);actionBar.addTab(actionBar.newTab().setText("娱乐").setTag(TYPE_YULE).setTabListener(this));actionBar.addTab(actionBar.newTab().setText("新闻").setTag(TYPE_NEWS).setTabListener(this));actionBar.addTab(actionBar.newTab().setText("体育").setTag(TYPE_SPORT).setTabListener(this));viewPager.setAdapter(new MyAdapter(getSupportFragmentManager()));viewPager.setOnPageChangeListener(this);}private static class MyAdapter extends FragmentPagerAdapter {// staticpublic MyAdapter(FragmentManager fm) {super(fm);}@Overridepublic Fragment getItem(int position) {return fragments.get(position);}@Overridepublic int getCount() {return fragments.size();}}@Overridepublic void onTabSelected(Tab tab, FragmentTransaction ft) {int tag = Integer.parseInt(tab.getTag().toString());//设置当前的viewpager的当前viewItemviewPager.setCurrentItem(tag);}@Overridepublic void onPageSelected(int position) {//滑动时设置actionbar的当前tabactionBar.setSelectedNavigationItem(position);}@Overridepublic void onPageScrollStateChanged(int state) {}@Overridepublic void onTabUnselected(Tab tab, FragmentTransaction ft) {}@Overridepublic void onTabReselected(Tab tab, FragmentTransaction ft) {}@Overridepublic void onPageScrolled(int position, float positionOffset,int positionOffsetPixels) {}}

4.FragmentStatePagerAdapter

当有大量页数时，使用该类型的适配器很合适，类似于listview，当页面不在可见，fragment对象有可能销毁，但是，这些fragment的状态信息被保存下来，类似于activity的状态保存，从而占用很少的内存。用法与FragmentPagerAdapter 类似