Fragment通信的那点事(Communicating with Fragments)

Fragment通信情况分为两种：

1.处于同一Activity中的Fragment通信，经典的例如Activity+ViewPager+Fragment

2.处于非同一Activity中的两个Fragment或一个Activity中的Fragment与另外的Activity通信

因为第二种较为简单，这里先说一说第二种个人解决方案，第二种直接采用receiver广播机制来通信（发送参数，更新界面等）

遇到第一种情况虽然也可以使用receiver广播来解决，但是广播机制肯定会涉及到线程开销的，所以从性能着想，采用google官方推荐的接口通信。

定义一个接口

为了让一个Fragment传达到它的Activity，可以在Fragment内部定义一个接口让Activity来实现。该Fragment的onAttach（）方法的生命周期过程中捕获接口实现，然后就可以调用接口的方法，以便与Activity进行沟通。

这里是Fragment与Activity通信的例子：

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");
        }
    }

...
}

从代码中可以看出Fragment捕获了Activity的接口实现，这是第一个Fragment已经完成了该有的通信操作，接下来应该由Activity将接受到的数据传递给另外一个Fragment了

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();
        }
    }
}

通过上面的例子，展示了Fragment与Fragment之间用接口来实现通信的功能，以后不能滥用广播了~~~