Fragment表示“碎片”，它的设计理念是将Activity划分为不同的区块，各区块可以是某个控件，也可以是由Fragment实现显示的部分。

【基本特性】1. 可以在布局中添加某个容器承载Fragment，具体的显示内容由Fragment实现2. Fragment可以被附加到容器中，也可以被其它Fragment替换，也可以被从容器中移除，无论是哪种操作，对于Fragment的宿主Activity及该Activity中其它的部分不会产生影响3. Fragment有独立的生命周期【创建流程】1. 自定义View，继承android.support.v4.app.Fragment2. 重写onCreateView()方法，确定需要显示的内容的View对象，并作为该方法的返回值【使用ViewPager+Fragment】1. 将Activity类修改为继承自FragmentActivity2. 自定义类，继承android.support.v4.app.FragmentPagerAdapter，并重写抽象方法3. 在自定义的FragmentPagerAdapter中定义构造方法时，需要FragmentManager对象，可以通过调用getSupportFragmentManager()方法获取4. 在自定义的FragmentPagerAdapter中的getItem()方法中，根据参数position创建不同的Fragment对象。【注意事项】1. 由于Fragment不是Context的子孙类，在Fragment中需要Context对象时，应该通过调用getActivity()获取其宿主Activity的对象，用于表示上下文对象

public class MainActivity extends FragmentActivity {    // 按钮：团购    private Button btnMenuDeal;    // 按钮：附近    private Button btnMenuNearby;    // 按钮：我的    private Button btnMenuMy;    // 按钮：更多    private Button btnMenuMore;    // Fragment容器    private FrameLayout flContainer;    // Fragment的Adapter    private FragmentPagerAdapter fragmentAdapter;    // 上次显示的Fragment的position，用于显示新Fragment时，把旧的移除    private int lastPosition;    // 上次显示的Fragment对象，用于显示新Fragment时，把旧的移除    private Object lastItem;        @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                // 初始化底部菜单的4个按钮        btnMenuDeal = (Button) findViewById(R.id.btn_menu_deal);        btnMenuNearby = (Button) findViewById(R.id.btn_menu_nearby);        btnMenuMy = (Button) findViewById(R.id.btn_menu_my);        btnMenuMore = (Button) findViewById(R.id.btn_menu_more);        // 为底部菜单的4个按钮配置点击监听        MenuButtonOnClickListener listener = new MenuButtonOnClickListener();        btnMenuDeal.setOnClickListener(listener);        btnMenuNearby.setOnClickListener(listener);        btnMenuMy.setOnClickListener(listener);        btnMenuMore.setOnClickListener(listener);        // 初始化Fragment容器：FrameLayout        flContainer = (FrameLayout) findViewById(R.id.fl_container);        // 为Fragment容器配置Adapter（仅当使用ViewPager作为容器时使用）        fragmentAdapter = new InnerPagerAdapter();        // flContainer.setAdapter(adapter);                // 默认选中第1个        selectMenuItem(btnMenuDeal);        // 手动执行监听器，以触发显示第1个Fragment        listener.onClick(btnMenuDeal);    }        private class InnerPagerAdapter extends FragmentPagerAdapter {        public InnerPagerAdapter() {            super(getSupportFragmentManager());        }        @Override        public Fragment getItem(int position) {            Fragment fragment = null;            switch (position) {            case 0:                fragment = new DealFragment();                break;            case 1:                fragment = new NearByFragment();                break;            case 2:                fragment = new MyFragment();                break;            case 3:                fragment = new MoreFragment();                break;            }            return fragment;        }        @Override        public int getCount() {            return 4;        }            }        /**     * Tab菜单点击事件监听器     */    private class MenuButtonOnClickListener implements View.OnClickListener {        @Override        public void onClick(View v) {            int position = 0;            switch (v.getId()) {            case R.id.btn_menu_deal:                position = 0;                selectMenuItem(btnMenuDeal);                break;                            case R.id.btn_menu_nearby:                position = 1;                selectMenuItem(btnMenuNearby);                break;                            case R.id.btn_menu_my:                position = 2;                selectMenuItem(btnMenuMy);                break;                            case R.id.btn_menu_more:                position = 3;                selectMenuItem(btnMenuMore);                break;            }                        // 如果已经显示了Fragment，则从容器中移除            if(lastItem != null) {                fragmentAdapter.destroyItem(flContainer, lastPosition, lastItem);            }            // 确定当前需要被显示的Fragment对象            Object fragment = fragmentAdapter.instantiateItem(flContainer, position);            // 记录下当前显示的Fragment的position            lastPosition = position;            // 记录下当前显示的Fragment            lastItem = fragment;            // 设置当前显示的Fragment            fragmentAdapter.setPrimaryItem(flContainer, 0, fragment);            // 更新显示            fragmentAdapter.finishUpdate(flContainer);        }            }            /**     * 选择底部菜单中的某一项     * @param v 被选中的项     */    private void selectMenuItem(View v) {        // 实现基本思路是选中1个，取消选中3个        // 具体实现时，可以先取消选中所有，然后选中1个        // 取消选中所有        btnMenuDeal.setSelected(false);        btnMenuNearby.setSelected(false);        btnMenuMy.setSelected(false);        btnMenuMore.setSelected(false);        // 选中参数对应的控件        v.setSelected(true);    }}

另一种方法实现fragment之间的切换：

@EActivity(resName="main_fragment")public class MainFragmentActivity extends FragmentActivity{    SportFragment sportFragment;    DiscoverFragment discoverFragment;    MessageFragment messageFragment;    MeFragment meFragment;        @ViewsById({R.id.btn_main_fragment_sport,    R.id.btn_main_fragment_discover,    R.id.btn_main_fragment_message,    R.id.btn_main_fragment_me})    ArrayList btnList=new ArrayList();        //放四个fragment    Fragment[] fragments=new Fragment[4];    /**     * 当前显示的是第几个fragment     */    int currentFragmentIndex=0;    int clickIndex=0;    @Override    public void onConfigurationChanged(Configuration newConfig) {    int orientation=    newConfig.orientation;    LogUtil.i("屏幕方向", "activity onConfigurationChanged"+orientation);        super.onConfigurationChanged(newConfig);    }    @Override    protected void onCreate(Bundle arg0) {        // TODO Auto-generated method stub        super.onCreate(arg0);        try {            LogUtil.i("屏幕方向", "activity onCreate");            sportFragment=new SportFragment();            discoverFragment=new DiscoverFragment();            messageFragment=new MessageFragment();            meFragment=new MeFragment();                        fragments[0]=sportFragment;            fragments[1]=discoverFragment;            fragments[2]=messageFragment;            fragments[3]=meFragment;                        FragmentManager manager=this.getSupportFragmentManager();            //Transaction事务            FragmentTransaction transaction=manager.beginTransaction();            //把sportFragment放到linearLayout            transaction.add(R.id.fragment_container, sportFragment);            transaction.show(sportFragment);            //提交            transaction.commit();                                } catch (Exception e) {            ExceptionUtil.handlerException(e);        }    }    //代码执行顺序 onCreate-->ViewsById-->AfterView    @AfterViews    public void addListener()    {        //设置当前按钮的状态        btnList.get(currentFragmentIndex).setSelected(true);                MyListener myListener=new MyListener();        for (Button btn:btnList)        {            btn.setOnClickListener(myListener);        }    }    class MyListener implements OnClickListener    {        @Override        public void onClick(View v) {                        try {                switch (v.getId()) {                case R.id.btn_main_fragment_sport:                    clickIndex=0;                    break;                case R.id.btn_main_fragment_discover:                    clickIndex=1;                    break;                case R.id.btn_main_fragment_message:                    clickIndex=2;                    break;                case R.id.btn_main_fragment_me:                    clickIndex=3;                    break;                }                if (clickIndex!=currentFragmentIndex)                {                    //单击别的按钮，显示另外一个fragment                    Fragment showFragment=fragments[clickIndex];                    FragmentTransaction transaction=getSupportFragmentManager().beginTransaction();                    if (!showFragment.isAdded())                    {                        //以前没有显示过                        transaction.add(R.id.fragment_container, showFragment);                                            }                    transaction.hide(fragments[currentFragmentIndex]);                    transaction.show(showFragment);                    transaction.commit();                    btnList.get(currentFragmentIndex).setSelected(false);                    btnList.get(clickIndex).setSelected(true);                                        currentFragmentIndex=clickIndex;                                    }            } catch (Exception e) {                ExceptionUtil.handlerException(e);            }        }            }}