fragment的使用

在运行的Activity中添加一个Fragment

一个处理Fragment的重要原则，Fragment必须有一个在布局中有一个让其寄存的View容器，特别是对那些运行时的Fragment。

以下是一个布局文件，每次显示一个Fragment。为了用一个Fragment替换另外一个，Activity的布局文件包含一个空的FrameLayout，作为Fragment容器使用。

1. res/layout/news_articles.xml:
2. <FrameLayoutxmlns:android="http://schemas.android.com/apk/res/android"
3.    android:id="@+id/fragment_container"
4.    android:layout_width="match_parent"
5.    android:layout_height="match_parent" />          

在Activity当中，利用getSupportFragmentManager()获取一个FragmentManager，以下是代码示例：

1. import android.os.Bundle;
2. import android.support.v4.app.FragmentActivity;
3. public class MainActivity extends FragmentActivity {
4.     @Override
5.     public voidonCreate(Bundle savedInstanceState) {
6.        super.onCreate(savedInstanceState);
7.         setContentView(R.layout.news_articles);
8.         // Checkthat the activity is using the layout version with
9.         // thefragment_container FrameLayout
10.         if(findViewById(R.id.fragment_container) != null) {
11.             //However, if we're being restored from a previous state,
12.             // thenwe don't need to do anything and should return or else
13.             // wecould end up with overlapping fragments.
14.             if(savedInstanceState != null) {
15.                return;
16.             }
17.             // Create an instance of ExampleFragment
18.            HeadlinesFragment firstFragment = new HeadlinesFragment();
19.             // Incase this activity was started with special instructions from an Intent,
20.             // passthe Intent's extras to the fragment as arguments
21.            firstFragment.setArguments(getIntent().getExtras());
22.             // Addthe fragment to the 'fragment_container' FrameLayout
23.            getSupportFragmentManager().beginTransaction()
24.                     .add(R.id.fragment_container,firstFragment).commit();
25.         }
26.     }
27. }

Fragment替换

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替换Fragment的流程和添加的流程类似，只不过需要利用replace方法替换add方法。

需要记住的是，当你是Fragment切换的时候，例如替换或者一处，最好让用户拥有返回或者撤销的机会

当你允许用户返回或者撤销Fragment操作的时候，你必须在调用FragmentTransaction之前调用addToBackStack。

以下是一个示例：

1. 1. // Create fragment and give it an argument specifying thearticle it should show
   2. ArticleFragment newFragment = new ArticleFragment();
   3. Bundle args = new Bundle();
   4. args.putInt(ArticleFragment.ARG_POSITION, position);
   5. newFragment.setArguments(args);
   6. FragmentTransaction transaction =getSupportFragmentManager().beginTransaction();
   7. // Replace whatever is in the fragment_container viewwith this fragment,
   8. // and add the transaction to the back stack so the usercan navigate back
   9. transaction.replace(R.id.fragment_container,newFragment);
   10. transaction.addToBackStack(null);
   11. // Commit the transaction
   12. transaction.commit();