android Fragments详解七:fragement示例

下例中实验了上面所讲的所有内容。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。

主activity创建layout。

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

主 activity的 layoutxml文档

<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。

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