Android Fragment详解(六)：Fragement示例

把条目添加到动作栏

你的fragment们可以向activity的菜单（按Manu键时出现的东西）添加项，同时也可向动作栏（界面中顶部的那个区域）添加条目，这都需通过实现方法onCreateOptionManu()来完成。

你从fragment添加到菜单的任何条目，都会出现在现有菜单项之后。Fragment之后可以通过方法onOptionsItemSelected()来响应自己的菜单项被选择的事件。

你也可以在fragemnt中注册一个view来提供快捷菜单（上下文菜单）。当用户要打开快捷菜单时，fragment的onCreateContextMenu()方法会被调用。当用户选择其中一项时，fragemnt的onContextItemSelected()方法会被调用。

注：尽管你的fragment可以分别收到它所添加的菜单项的选中事件，但是activity才是第一个接收这些事件的家伙，只有当activity对某个事件置之不理时，fragment才能接收到这个事件，对于菜单和快捷菜单都是这样。

下例中实验了之前所讲的所有内容。此例有一个activity，其含有两个fragment。一个显示莎士比亚剧的播放曲目，另一个显示选中曲目的摘要。此例还演示了如何跟据屏幕大小配置fragment。

MainActivity:

@Override  
protectedvoid onCreate(Bundle savedInstanceState) {  
   super.onCreate(savedInstanceState);  
  
   setContentView(R.layout.fragment_layout);  
} 

Layout.xml:

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
        android:orientation="horizontal"  
        android:layout_width="match_parent" android:layout_height="match_parent">  
      
        <fragment class="com.example.android.apis.app.FragmentLayout$TitlesFragment"  
                android:id="@+id/titles" android:layout_weight="1"  
                android:layout_width="0px" android:layout_height="match_parent" />  
      
        <FrameLayout android:id="@+id/details" android:layout_weight="1"  
                android:layout_width="0px" android:layout_height="match_parent"  
                android:background="?android:attr/detailsElementBackground" />  
      
    </LinearLayout>  

系统在activity加载此layout时初始化TitlesFragment（用于显示标题列表），TitlesFragment的右边是一个FrameLayout，用于存放显示摘要的fragment，但是现在它还是空的，fragment只有当用户选择了一项标题后，摘要fragment才会被放到FrameLayout中。

然而，并不是所有的屏幕都有足够的宽度来容纳标题列表和摘要。所以，上述layout只用于横屏，现把它存放于ret/layout-land/fragment_layout.xml。

之外，当用于竖屏时，系统使用下面的layout，它存放于ret/layout/fragment_layout.xml：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="match_parent" android:layout_height="match_parent">  
    <fragment class="com.example.android.apis.app.FragmentLayout$TitlesFragment"  
            android:id="@+id/titles"  
            android:layout_width="match_parent" android:layout_height="match_parent" />  
</FrameLayout> 

这个 layout只包含 TitlesFragment。这表示当使用竖屏时，只显示标题列表。当用户选中一项时，程序会启动一个新的 activity去显示摘要，而不是加载第二个 fragment。

下一步，你会看到Fragment类的实现。第一个是TitlesFragment，它从ListFragment派生，大部分列表的功能由ListFragment提供。

当用户选择一个Title时，代码需要做出两种行为，一种是在同一个activity中显示创建并显示摘要fragment，另一种是启动一个新的activity。

    public static class TitlesFragment extends ListFragment {  
        boolean mDualPane;  
        int mCurCheckPosition = 0;  
      
        @Override  
        public void onActivityCreated(Bundle savedInstanceState) {  
            super.onActivityCreated(savedInstanceState);  
      
            // Populate list with our static array of titles.  
            setListAdapter(new ArrayAdapter<String>(getActivity(),  
                    android.R.layout.simple_list_item_activated_1, Shakespeare.TITLES));  
      
            // Check to see if we have a frame in which to embed the details  
            // fragment directly in the containing UI.  
            View detailsFrame = getActivity().findViewById(R.id.details);  
            mDualPane = detailsFrame != null && detailsFrame.getVisibility() == View.VISIBLE;  
      
            if (savedInstanceState != null) {  
                // Restore last state for checked position.  
                mCurCheckPosition = savedInstanceState.getInt("curChoice", 0);  
            }  
      
            if (mDualPane) {  
                // In dual-pane mode, the list view highlights the selected item.  
                getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);  
                // Make sure our UI is in the correct state.  
                showDetails(mCurCheckPosition);  
            }  
        }  
      
        @Override  
        public void onSaveInstanceState(Bundle outState) {  
            super.onSaveInstanceState(outState);  
            outState.putInt("curChoice", mCurCheckPosition);  
        }  
      
        @Override  
        public void onListItemClick(ListView l, View v, int position, long id) {  
            showDetails(position);  
        }  
      
        /** 
         * Helper function to show the details of a selected item, either by 
         * displaying a fragment in-place in the current UI, or starting a 
         * whole new activity in which it is displayed. 
         */  
        void showDetails(int index) {  
            mCurCheckPosition = index;  
      
            if (mDualPane) {  
                // We can display everything in-place with fragments, so update  
                // the list to highlight the selected item and show the data.  
                getListView().setItemChecked(index, true);  
      
                // Check what fragment is currently shown, replace if needed.  
                DetailsFragment details = (DetailsFragment)  
                        getFragmentManager().findFragmentById(R.id.details);  
                if (details == null || details.getShownIndex() != index) {  
                    // Make new fragment to show this selection.  
                    details = DetailsFragment.newInstance(index);  
      
                    // Execute a transaction, replacing any existing fragment  
                    // with this one inside the frame.  
                    FragmentTransaction ft = getFragmentManager().beginTransaction();  
                    ft.replace(R.id.details, details);  
                    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);  
                    ft.commit();  
                }  
      
            } else {  
                // Otherwise we need to launch a new activity to display  
                // the dialog fragment with selected text.  
                Intent intent = new Intent();  
                intent.setClass(getActivity(), DetailsActivity.class);  
                intent.putExtra("index", index);  
                startActivity(intent);  
            }  
        }  

第二个 fragment， DetailsFragment显示被选择的 Title的摘要：

    public static class DetailsFragment extends Fragment {  
        /** 
         * Create a new instance of DetailsFragment, initialized to 
         * show the text at 'index'. 
         */  
        public static DetailsFragment newInstance(int index) {  
            DetailsFragment f = new DetailsFragment();  
      
            // Supply index input as an argument.  
            Bundle args = new Bundle();  
            args.putInt("index", index);  
            f.setArguments(args);  
      
            return f;  
        }  
      
        public int getShownIndex() {  
            return getArguments().getInt("index", 0);  
        }  
      
        @Override  
        public View onCreateView(LayoutInflater inflater, ViewGroup container,  
                Bundle savedInstanceState) {  
            if (container == null) {  
                // We have different layouts, and in one of them this  
                // fragment's containing frame doesn't exist.  The fragment  
                // may still be created from its saved state, but there is  
                // no reason to try to create its view hierarchy because it  
                // won't be displayed.  Note this is not needed -- we could  
                // just run the code below, where we would create and return  
                // the view hierarchy; it would just never be used.  
                return null;  
            }  
      
            ScrollView scroller = new ScrollView(getActivity());  
            TextView text = new TextView(getActivity());  
            int padding = (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,  
                    4, getActivity().getResources().getDisplayMetrics());  
            text.setPadding(padding, padding, padding, padding);  
            scroller.addView(text);  
            text.setText(Shakespeare.DIALOGUE[getShownIndex()]);  
            return scroller;  
        }  
    }  

如果当前的 layout没有 R.id.detailsView（它被用于 DetailsFragment的容器），那么程序就启动 DetailsActivity来显示摘要。

下面是DetailsActivity，它只是简单地嵌入DetailsFragment来显示摘要。

    public static class DetailsActivity extends Activity {  
      
        @Override  
        protected void onCreate(Bundle savedInstanceState) {  
            super.onCreate(savedInstanceState);  
      
            if (getResources().getConfiguration().orientation  
                    == Configuration.ORIENTATION_LANDSCAPE) {  
                // If the screen is now in landscape mode, we can show the  
                // dialog in-line with the list so we don't need this activity.  
                finish();  
                return;  
            }  
      
            if (savedInstanceState == null) {  
                // During initial setup, plug in the details fragment.  
                DetailsFragment details = new DetailsFragment();  
                details.setArguments(getIntent().getExtras());  
                getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();  
            }  
        }  
    }  

注意这个 activity在检测到是竖屏时会结束自己，于是主 activity会接管它并显示出 TitlesFragment和 DetailsFragment。这可以在用户在竖屏时显示在 TitleFragment，但用户旋转了屏幕，使显示变成了横屏。