Android Training--Fragment

动态添加Fragment

public class MainActivity extends FragmentActivity {
&Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.news_articles);

// 确认 Activity 使用的布局版本包含
// fragment_container FrameLayout
if (findViewById(R.id.fragment_container) != null) {

// 不过，如果我们要从先前的状态还原，
// 则无需执行任何操作而应返回
// 否则就会得到重叠的 Fragment 。
if (savedInstanceState != null) {
return;
}

// 创建一个要放入 Activity 布局中的新 Fragment
HeadlinesFragment firstFragment = new HeadlinesFragment();

// 如果此 Activity 是通过 Intent 发出的特殊指令来启动的，
// 请将该 Intent 的 extras 以参数形式传递给该 Fragment
firstFragment.setArguments(getIntent().getExtras());

// 将该 Fragment 添加到“fragment_container”FrameLayout 中
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
}
}
}

Communicating with Other Fragments

In order to reuse the Fragment UI components, you should build each as a completely self-contained, modular component that defines its own layout and behavior. Once you have defined these reusable Fragments, you can associate them with an Activity and connect them with the application logic to realize the overall composite UI.

Often you will want one Fragment to communicate with another, for example to change the content based on a user event. All Fragment-to-Fragment communication is done through the associated Activity. Two Fragments should never communicate directly.

Define an Interface

To allow a Fragment to communicate up to its Activity, you can define an interface in the Fragment class and implement it within the Activity. The Fragment captures the interface implementation during its onAttach() lifecycle method and can then call the Interface methods in order to communicate with the Activity.

Here is an example of Fragment to Activity communication:

public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;

// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
public void onArticleSelected(int position);
}

@Override
public void onAttach(Activity activity) {
super.onAttach(activity);

// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mCallback = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}

...
}

Now the fragment can deliver messages to the activity by calling the onArticleSelected() method (or other methods in the interface) using the mCallback instance of the OnHeadlineSelectedListener interface.

For example, the following method in the fragment is called when the user clicks on a list item. The fragment uses the callback interface to deliver the event to the parent activity.

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Send the event to the host activity
mCallback.onArticleSelected(position);
}

Deliver a Message to a Fragment

The host activity can deliver messages to a fragment by capturing the Fragment instance with findFragmentById(), then directly call the fragment’s public methods.

For instance, imagine that the activity shown above may contain another fragment that’s used to display the item specified by the data returned in the above callback method. In this case, the activity can pass the information received in the callback method to the other fragment that will display the item:

public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
...

public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Do something here to display that article

ArticleFragment articleFrag = (ArticleFragment)
getSupportFragmentManager().findFragmentById(R.id.article_fragment);

if (articleFrag != null) {
// If article frag is available, we're in two-pane layout...

// Call a method in the ArticleFragment to update its content
articleFrag.updateArticleView(position);
} else {
// Otherwise, we're in the one-pane layout and must swap frags...

// Create fragment and give it an argument for the selected article
ArticleFragment newFragment = new ArticleFragment();
Bundle args = new Bundle();
args.putInt(ArticleFragment.ARG_POSITION, position);
newFragment.setArguments(args);

FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);

// Commit the transaction
transaction.commit();
}
}
}

以上为google官方文档,其实也可以在FragmentA中mActivity = getActivity()获取Activity实例,再在Activity中创建方法同时获取findFragmentByTag获取FragmentB, FragmentA可以通过mActivity调用相应方法来相应处理两个Fragment之间的交互.

额…又思考了下, 发现上面说的方案应该就是官方文档里面着重强调的不要形成的Fragment间交互情况, 还是使用接口回调的方法吧.