Android学习笔记十五.深入理解fragment(三) 之《兼容多分辨率的应用》实战

package com.example.android_fragment_1;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.MenuItem;
public class BookDetailActivity extends Activity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
 //1.指定加载/res/layout目录下的activity_book_detail.xml布局文件
  setContentView(R.layout.activity_book_detail);
 //2.将ActionBar上应用图标转换成可点击的按钮
  getActionBar().setDisplayHomeAsUpEnabled(true);
  if(savedInstanceState==null)
  {
   //a.创建BookDetailFragment对象
   BookDetailFragment fragment=new BookDetailFragment();
   //b.创建Bundle对象
   Bundle arguments=new Bundle();
   arguments.putInt(BookDetailFragment.ITEM_ID, getIntent()
     .getIntExtra(BookDetailFragment.ITEM_ID,0));
   //c.向Fragment传入参数
   fragment.setArguments(arguments);
   //d.指定fragment添加到book_detail_container容器中
   getFragmentManager().beginTransaction()
     .add(R.id.book_detail_container, fragment).commit();
  }
 }
 //3.按下图标响应
 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
  // TODO Auto-generated method stub
  if(item.getItemId()==android.R.id.home)
  {
   //a.创建启动BookListActivity的Intent
   Intent intent=new Intent(this,BookListActivity.class);
   //b.添加额外的Flag，将Activity栈中处于FirstActivity之上的Activity弹出
   intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
   //c.启动intent对应的Activity
   startActivity(intent);
   return true;
  }
  return super.onOptionsItemSelected(item);
 
 }
  /res/layout目录下的activity_book_detail.xml布局文件
    该界面布局文件内只定义了一个ID名为book_detail_container的FrameLayout，用于显示图书详情。
 <?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/book_detail_container" >
</FrameLayout>

package com.example.android_fragment_1;
import android.app.Activity;
import android.app.ListFragment;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class BookListFragment extends ListFragment {
  //1.定义一个回调接口Callback,用于实现该Fragment与它所在的Activity交互(注意：该接口的实现需要在Activit中)
 private Callbacks mCallbacks;	//Callbacks接口对象
 public interface Callbacks
 {
  public void onItemSelected(Integer id);	//参数为Map集合的键
 }
 
 //2.onCreate方法中为该ListFragment设置Adapter，让该ListFragment显示该Adapter所提供的多个列表项
 @Override
 public void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  setListAdapter(new ArrayAdapter<BookContent.Book>(getActivity(),//
    android.R.layout.simple_list_item_activated_1,
    android.R.id.text1,
    BookContent.ITEMS));	 //
 }
 
 //3.调用该方法将Fragment添加并显示到Acitvity中
 @Override
 public void onAttach(Activity activity) {
  // TODO Auto-generated method stub
  super.onAttach(activity);
  //a.如果Activity中没有实现Callbacks接口，抛出异常
  if(!(activity instanceof Callbacks))
  {
   throw new IllegalStateException("异常:BookListFragment所在的Activity必须实现Callback接口！");
  }
  //把该Activity当成Callbacks对象(就是这一句导致出现NullPointerException错误)
        mCallbacks=(Callbacks)activity;
 }
 
 //4.当该Fragment从他所属的Acitivity中被删除时，调用该方法
 @Override
 public void onDetach() {
  super.onDetach();
  mCallbacks=null;	//将mCallbacks赋值为null
 }
 
 //5.当用户单击某列表项时激发该回调方法
 @Override
 public void onListItemClick(ListView l, View v, int position, long id) {
  super.onListItemClick(l, v, position, id);
  mCallbacks.onItemSelected(BookContent.ITEMS.get(position).id);//激发mCallbacks接口的onItemSelected方法
 }
public void setActivateOnItemClick(boolean activateOnItemClick) {
getListView().setChoiceMode(activateOnItemClick ? ListView.CHOICE_MODE_SINGLE:ListView.CHOICE_MODE_NONE);
 }
}

  <application 
        .......>
            <activity
            android:name=".BookListActivity"
            android:label="@string/app_name" >
                <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
                </intent-filter>
            </activity>
             <activity
            android:name=".BookDetailActivity"
            android:label="@string/app_name" >
            </activity>
    </application>
</manifest>