Activity和Fragment之前的通信

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当在Activity中使用了Fragment的时候，始终要考虑的一个问题就是Fragment和Activity要如何通信。所谓的通信就是当Fragment中触发了某些事件之后，或者数据发生变化之后，如何通知Activity。

请先看下面的class图示：

diagram
来解释一下图中的意思：
这里的FragmentCallBack 是一个接口定义了Fragment 和Activity之间通信时候调用的方法。FragmentLearningActivity本身实现了这个callback接口，从泛型角度，它就是这个接口的具体实现类。
而在TopFragment中定义了一个FragmentCallBack的实例callBack，所以当初始化的TopFragment的时候，就把Fragment所属的Activity也就是FragmentLearningActivity注册给这个实例callBack。

当TopFragment有事件触发的时候，就调用这个接口实例callBack调用invokeItemSelect方法，因为callBack就是泛指FragmentLearningActivity，所以FragmentLearningActivity中的invokeItemSelect就会触发，这通过这个方法就可以实现具体的通信。
其实这种方式在popupwindow和Activity通信方式也会被用到。所以大家要经常思考加以扩展和复用。
下面是一个Fragment和Activity之间通信的例子：
TopFragment实现：

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package com.learning.coolbeetle.fragment;
 
import android.R;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
 
import com.learning.coolbeetle.model.BookContent;
 
 
 
@SuppressLint("NewApi")
public class TopFragment extends Fragment implements OnItemClickListener{
    
 
    ListView listview;
    
    
    FragmentCallBack callBack;
    
    
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        
        View  view  =  inflater.inflate(com.learning.coolbeetle.R.layout.fragment_top, null);
        this.listview = (ListView) view.findViewById(com.learning.coolbeetle.R.id.top_list);
        this.listview.setOnItemClickListener(this);
        
        listview.setAdapter(new ArrayAdapter(this.getActivity(), R.layout.simple_list_item_activated_1, R.id.text1, BookContent.ITEMS));
        return view;
    }
    
    
 
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        if(!(activity instanceof FragmentCallBack)){
            throw new IllegalStateException("Activity must implement FragmentCallBack interface!");
        }
        this.callBack = (FragmentCallBack) activity;
    }
 
    @Override
    public void onDetach() {
        super.onDetach();
        callBack = null;
    }
 
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {
        callBack.invokeItemSelect(BookContent.ITEMS.get(position).getId());
        
    }
 
    public FragmentCallBack getCallBack() {
        return callBack;
    }
 
    public void setCallBack(FragmentCallBack callBack) {
        this.callBack = callBack;
    }
    
}

FragmentCallBack接口

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packagecom.learning.coolbeetle.fragment;
publicinterfaceFragmentCallBack{
    publicvoidinvokeItemSelect(Integerid);
}

FragmentLearningActivity的代码实现：

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package com.learning.coolbeetle;
 
import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
 
import com.learning.coolbeetle.fragment.DetailFragment;
import com.learning.coolbeetle.fragment.FragmentCallBack;
import com.learning.coolbeetle.model.Book;
import com.learning.coolbeetle.model.BookContent;
 
public class FragmentLearningActivity extends Activity implements FragmentCallBack{
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_learning);
 
    }
 
    @SuppressLint("NewApi")
    @Override
    public void invokeItemSelect(Integer id) {
        
        Book selectedBook = BookContent.MAP_ITEMS.get(id);
        if(selectedBook != null){
            Bundle bundle = new Bundle();
            bundle.putInt("bookId", id);
            DetailFragment detailFragment = new DetailFragment();
            detailFragment.setArguments(bundle);
            
            this.getFragmentManager().beginTransaction().replace(R.id.detail_fragment, detailFragment).commit();
        }
        
    }
 
 
}

Activity布局文件中添加fragment：

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<?xmlversion="1.0"encoding="utf-8"?>
<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
  <fragment
      android:id="@+id/top_fragment"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      class="com.learning.coolbeetle.fragment.TopFragment"/>
 
</RelativeLayout>

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