在Activity中添加Fragment

一、在Activity布局文件中静态添加Fragment：

res/layout-large/news_articles.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <fragment android:name="com.example.android.fragments.HeadlinesFragment"
              android:id="@+id/headlines_fragment"
              android:layout_weight="1"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

    <fragment android:name="com.example.android.fragments.ArticleFragment"
              android:id="@+id/article_fragment"
              android:layout_weight="2"
              android:layout_width="0dp"
              android:layout_height="match_parent" />

</LinearLayout>

二、为Fragment指定布局文件：

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.ViewGroup;

public class ArticleFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.article_view, container, false);
    }
}

每个Fragment实例需要关联到一个FragmeActivity，所以要添加Fragment的自定义Activity需继承FragmentActivity；
因为FragmentActivity是定义在API 11 以后的v4 Support Library,且继承自Activity，所以在API 11+的平台上可以直接继承Activity。
如果使用的库是v7 appcompat library,应该继承AppCompatActivity，它是FragmentActivity的子类。

三.动态添加Fragment：注：Activity必须包含一个view容器，用来添加Fragment组件，如：
res/layout/news_articles.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

代码中动态添加：用到FragmentManager和FragmentTransaction类：

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;

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

        // Check that the activity is using the layout version with
        // the fragment_container FrameLayout
        if (findViewById(R.id.fragment_container) != null) {

            // However, if we're being restored from a previous state,
            // then we don't need to do anything and should return or else
            // we could end up with overlapping fragments.
            if (savedInstanceState != null) {
                return;
            }

            // Create a new Fragment to be placed in the activity layout
            HeadlinesFragment firstFragment = new HeadlinesFragment();

            // In case this activity was started with special instructions from an
            // Intent, pass the Intent's extras to the fragment as arguments
            firstFragment.setArguments(getIntent().getExtras());

            // Add the fragment to the 'fragment_container' FrameLayout
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.fragment_container, firstFragment).commit();
        }
    }
}

一定要记得调用commit（）方法。

四、动态替换Fragment：

// Create fragment and give it an argument specifying the article it should show
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();

五、Fragment之间通信：

注：Fragment之间的通信是通过他们关联的Activity进行的，两个Fragment之间不能直接通信
为了让一个Fragment与和它关联的Activity通信，可以在Fragment类中定义一个接口,Activity
类中实现该接口，然后Fragment在它的onAttach()生命周期方法中实例化接口，用该实例去调用
接口中的方法，实现通信，如下所示：

Fragment定义接口：

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");
        }
    }

    ...
}

Activity实现接口：

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
    }
}

调用方法：

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

六.Activity可以调用findFragmentById()方法获取关联于它的Fragment实例，然后可以调用该Fragment的public方法，如：

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

七、Fragment生命周期方法：
onAttach(): 当该Fragment关联到Activity时调用，Activity作为参数传入；
oncreate(): 与Activity的oncreate（）方法一样，实例化该Fragment调用；
oncreateView():创建Fragment自身布局时调用；
onActivityCreated():当与之关联的Activity的oncreate()方法返回时调用；
onStart(),onResume(),onStop(),onPause():这些方法跟Activity的生命周期方法一样；
onDestroyView():与oncreateView()方法相对应；
onDetach（）：当与Activity接触关联时调用，与onAttach()相对应。

只有当与之关联的Activity处于resumed状态时，Fragment的生命周期方法才可以独立的改变；
否则要受到与之关联的Activity的生命周期方法的限制。

附生命周期图:

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