Fragemnt

1. 创建一个Fragment

一个空的 FrameLayout作为fragment的容器

article_view.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" /

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);
         }
}

2. 用XML将fragment添加到activity

news_articles.xml

<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.android.fragments.ArticleFragment"
android:id="@+id/article_fragment"

android:layout_width="match_parent" android:layout_height="match_parent" />
</LinearLayout>

然后将这个布局文件用到你的activity中

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);
}
}

注意:如果你用的是 v7 appcompat library，你的activity应该改为继承ActionBarActivity，ActionBarActivity是FragmentActivity
的一个子类

3. 在activity运行时添加添加fragment

activity 可以移除（在XML布局中用 <fragment>  定义的fragment)或者用另外一个(HeadlinesFragment为编写)来替换它

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" /

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

//id 是 1 中的xml布局的id
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
ArticleFragment firstFragment = new ArticleFragment();
// 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();
}
}
}

Fragment替换

// 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);

//注意，后退键，调用destoryed;故 你必须在FragmentTransaction提交前调用addToBackStack()方法（放入栈中），调用的是stopped方法
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();

4 Fragments之间的交互

为了让fragment与activity交互， 你可以在Fragment 类中定义一个接口，并且在activity中实现这个接口。 Fragment在他们生命周期的onAttach()方法中捕获接口的实现，然后调用接口的方法来与Activity交互

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");
}
}
...
}

Fragment就可以通过调用 OnHeadlineSelectedListener  接口实例的 mCallback  中的 onArticleSelected()  （也可以是
其它方法）方法与activity传递消息。

举个例子，在fragment中的下面的方法在用户点击列表条目时被调用，fragment 用回调接口来传递事件给父Activity.

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

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
}
}

activity可以把从fragment回调方法中接收到的信息传递给新的Fragment

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();
}
}
}