API Guides - App Components

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Activities //TODO

Fragments

每个activity有一个back stack，里面存放的是 fragment transaction。

fragment必须放入activity （实际放入ViewGroup），状态直接受activity影响。

可用代码创建Fragment，也可用xml <fragment>元素

要求 API Level 11

fragment transaction 即 add, remove, replace a fragment

Fragments.Design Philosophy (done)

Creating a Fragment

1. 创建Fragment 子类，修改回调函数（ onCreate(), onStart(), onPause(), onStop）

2. 通常要覆盖onCreate(),  onCreateView()  -> 第一次绘制UI时，返回root of your UI 也可返回null(无UI），onPause()

3. 可以继承的Fragment子类：DialogFragment,  ListFragment, PreferenceFragment

public static class ExampleFragment extends Fragment {@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {// Inflate the layout for this fragmentreturn inflater.inflate(R.layout.example_fragment, container, false);}
}

注：LayoutInflater由参数提供。注意第三个参数为false。

4. 添加到layout： 1) 用xml (静态方式）  2）用代码（动态方式， FragmentTransaction类，

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="horizontal"android:layout_width="match_parent"android:layout_height="match_parent"><fragment android:name="com.example.news.ArticleListFragment"android:id="@+id/list"android:layout_weight="1"android:layout_width="0dp"android:layout_height="match_parent" /><fragment android:name="com.example.news.ArticleReaderFragment"android:id="@+id/viewer"android:layout_weight="2"android:layout_width="0dp"android:layout_height="match_parent" />
</LinearLayout>

代码方式：

FragmentManager fragmentManager = getFragmentManager()
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();ExampleFragment fragment = new ExampleFragment();
fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();

fragment还可以没有UI，提供一种后台服务. 用FragmentTransaction.add(Fragment, String)版本的函数，而且无需实现 onCreateView()，而且没有id，只能用string tag访问。

findFragmentByTag()

后台fragment的例子：FragmentRetainInstance.java

Managing Fragments

用 FragmentManager 管理 fragment, getFragmentManager()

FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

(builder模式)

调用commin()之前，可用 addToBackStack()，将transanction放入 back stack.

// Create new fragment and transaction
Fragment newFragment = new ExampleFragment();
FragmentTransaction transaction = getFragmentManager().beginTransaction();// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);// Commit the transaction
transaction.commit();

commin()之前使用 setTransition() 可设置动画

Communicating with the Activity

public static class FragmentA extends ListFragment {...// Container Activity must implement this interfacepublic interface OnArticleSelectedListener {public void onArticleSelected(Uri articleUri);}...
}

public static class FragmentA extends ListFragment {OnArticleSelectedListener mListener;...@Overridepublic void onAttach(Activity activity) {super.onAttach(activity);try {mListener = (OnArticleSelectedListener) activity;} catch (ClassCastException e) {throw new ClassCastException(activity.toString() + " must implement OnArticleSelectedListener");}}...
}

public static class FragmentA extends ListFragment {OnArticleSelectedListener mListener;...@Overridepublic void onListItemClick(ListView l, View v, int position, long id) {// Append the clicked item's row ID with the content provider UriUri noteUri = ContentUris.withAppendedId(ArticleColumns.CONTENT_URI, id);// Send the event and Uri to the host activitymListener.onArticleSelected(noteUri);}...
}

fragment 还可以给Action Bar 增加按钮， 具体

Adding items to the Action Bar //TODO

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