viewpager的基本用法

ViewPager繼承自ViewGroup，用以實現頁面的左右滑動。

1）ViewPager類直接繼承了ViewGroup類，所有它是一個容器類，可以在其中添加其他的view類。

2）ViewPager類需要一個PagerAdapter適配器類給它提供數據。

3）ViewPager經常和Fragment一起使用，並且提供了專門的FragmentPagerAdapter和FragmentStatePagerAdapter類供Fragment中的ViewPager使用。

在編寫ViewPager的應用的使用，還需要使用兩個組件類分別是PagerTitleStrip類和PagerTabStrip類，PagerTitleStrip類直接繼承自ViewGroup類，而PagerTabStrip類繼承PagerTitleStrip類，所以這兩個類也是容器類。但是有一點需要注意，在定義XML的layout的時候，這兩個類必須是ViewPager標籤的子標籤，不然會出錯。

fragment_collection_object.xml必不可少

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_collection_demo_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v4.view.PagerTitleStrip android:id="@+id/pager_title_strip"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="top"
        android:background="#33b5e5"
        android:textColor="#fff"
        android:paddingTop="4dp"
        android:paddingBottom="4dp" />

</android.support.v4.view.ViewPager>

實現原理:
PagerTitleStrip控制頂部條狀標題欄顯示效果，下方白色區域由fragment控制顯示效果。整個屏幕都放在容器viewpager中顯示。

主要類共5個：
CollectionDemoActivity.java，顯示控制頁面
activity_collection_demo.xml，顯示頁面的xml
DemoCollectionPagerAdapter.java，viewpager的數據填充adapter
DemoObjectFragment.java，數字顯示控制頁面
fragment_collection_object.xml，fragment的xml佈局

/** 顯示數字的Fragment
*/

    public static class DemoObjectFragment extends Fragment {

        public static final String ARG_OBJECT = "object";

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_collection_object, container, false);
            Bundle args = getArguments();
            ((TextView) rootView.findViewById(android.R.id.text1)).setText(
                    Integer.toString(args.getInt(ARG_OBJECT)));
            return rootView;
        }
    }

/**填充viewpager
*/

    public static class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {

        public DemoCollectionPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int i) {
            Fragment fragment = new DemoObjectFragment();
            Bundle args = new Bundle();
            args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public int getCount() {
            //有100個子項
            return 100;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return "OBJECT " + (position + 1);
        }
    }

//主activity

public class CollectionDemoActivity extends FragmentActivity {


    DemoCollectionPagerAdapter mDemoCollectionPagerAdapter;

    ViewPager mViewPager;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_collection_demo);

        mDemoCollectionPagerAdapter = new DemoCollectionPagerAdapter(getSupportFragmentManager());
        mViewPager = (ViewPager) findViewById(R.id.activity_collection_demo_pager);
        mViewPager.setAdapter(mDemoCollectionPagerAdapter);

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                // This is called when the Home (Up) button is pressed in the action bar.
                // Create a simple intent that starts the hierarchical parent activity and
                // use NavUtils in the Support Package to ensure proper handling of Up.
                Intent upIntent = new Intent(this, MainActivity.class);
                if (NavUtils.shouldUpRecreateTask(this, upIntent)) {
                    // This activity is not part of the application's task, so create a new task
                    // with a synthesized back stack.
                    TaskStackBuilder.from(this)
                            // If there are ancestor activities, they should be added here.
                            .addNextIntent(upIntent)
                            .startActivities();
                    finish();
                } else {
                    // This activity is part of the application's task, so simply
                    // navigate up to the hierarchical parent activity.
                    NavUtils.navigateUpTo(this, upIntent);
                }
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
   }

fragment_collection_object.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/text1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:textSize="128sp"
    android:padding="32dp" />