学习Android Studio开发工具之Activity2（&Fragment）

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本篇是介绍Google推荐使用的fragment以及其与activity的通信。

新建一个BlankFragment，



其中自动生成的代码如下：

package com.hitsz.xiaokai.fragmentcom;

import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link BlankFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link BlankFragment#newInstance} factory method to
* create an instance of this fragment.
* 这里是说实现子Fragment需要继承Fragment，这里是Google推荐的模板，在fragment里定义一个接口，然后它所依附的activity必须实现这个接口来完成相应的交互事件。
* 对于Fragment本身是使用工厂方法来创建实例的。
*/
public class BlankFragment extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
//此处声明Fragment对应变量，一般是布局控件
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;

//接口引用
private OnFragmentInteractionListener mListener;

public BlankFragment() {
// Required empty public constructor
}

/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment BlankFragment.
* 使用相应的参数返回工厂方法创建的Fragment
*/
// TODO: Rename and change types and number of parameters
public static BlankFragment newInstance(String param1, String param2) {
BlankFragment fragment = new BlankFragment();
//使用Bundle传递数据
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
//加载特定布局文件到布局容器中
return inflater.inflate(R.layout.fragment_blank, container, false);
}

// TODO: Rename method, update argument and hook method into UI event
//更新参数到ui
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}

@Override
public void onAttach(Context context) {
super.onAttach(context);
//判断activity是否实现了内部接口，如果没有实现抛出异常
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
//解除依附关系，同时将接口对象置空，方便垃圾回收
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}

/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p/>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
* 此接口必须被activity实现
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}

这里拿官网给的demo作为演示：



布局文件layout/article_view.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/article"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp"
android:textSize="18sp" />

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" />

layout_large/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" />

显示数据Ipsum.java

package com.hitsz.xiaokai.fragmentcom;

public class Ipsum {

static String[] Headlines = {
"Article One",
"Article Two"
};

static String[] Articles = {
"Article One\n\nExcepteur pour-over occaecat squid biodiesel umami gastropub, nulla laborum salvia dreamcatcher fanny pack. Ullamco culpa retro ea, trust fund excepteur eiusmod direct trade banksy nisi lo-fi cray messenger bag. Nesciunt esse carles selvage put a bird on it gluten-free, wes anderson ut trust fund twee occupy viral. Laboris small batch scenester pork belly, leggings ut farm-to-table aliquip yr nostrud iphone viral next level. Craft beer dreamcatcher pinterest truffaut ethnic, authentic brunch. Esse single-origin coffee banksy do next level tempor. Velit synth dreamcatcher, magna shoreditch in american apparel messenger bag narwhal PBR ennui farm-to-table.",
"Article Two\n\nVinyl williamsburg non velit, master cleanse four loko banh mi. Enim kogi keytar trust fund pop-up portland gentrify. Non ea typewriter dolore deserunt Austin. Ad magna ethical kogi mixtape next level. Aliqua pork belly thundercats, ut pop-up tattooed dreamcatcher kogi accusamus photo booth irony portland. Semiotics brunch ut locavore irure, enim etsy laborum stumptown carles gentrify post-ironic cray. Butcher 3 wolf moon blog synth, vegan carles odd future."
};
}

导航Fragment，继承自ListFragment，自带listview。

HeadlinesFragment.java

package com.hitsz.xiaokai.fragmentcom;

import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class HeadlinesFragment extends ListFragment {
//定义内部接口引用
OnHeadlineSelectedListener mCallback;

// The container Activity must implement this interface so the frag can deliver messages
public interface OnHeadlineSelectedListener {
/** Called by HeadlinesFragment when a list item is selected，当点击list item时回调，携带点击位置信息
*/
public void onArticleSelected(int position);
}

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

// We need to use a different list item layout for devices older than Honeycomb
int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;

// Create an array adapter for the list view, using the Ipsum headlines array 创建一个适配器ArrayAdapter<String>显示listview内容
setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines));
}

@Override
public void onStart() {
super.onStart();

// When in two-pane layout, set the listview to highlight the selected list item
// (We do this during onStart because at the point the listview is available.)
//根据id获取Fragment，需要在布局文件中使用Fragment标签加载Fragment
if (getFragmentManager().findFragmentById(R.id.article_fragment) != null) {
getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
}
}

@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.确保依附的activity实现接口
try {
mCallback = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Notify the parent activity of selected item
//通知activity选中的item
mCallback.onArticleSelected(position);

// Set the item as checked to be highlighted when in two-pane layout,设为高亮
getListView().setItemChecked(position, true);
}
}

显示详细内容的ArticleFragment.java

package com.hitsz.xiaokai.fragmentcom;

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

public class ArticleFragment extends Fragment {
//Fragment通信参数
final static String ARG_POSITION = "position";
int mCurrentPosition = -1;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {

// If activity recreated (such as from screen rotate), restore
// the previous article selection set by onSaveInstanceState().
// This is primarily necessary when in the two-pane layout.考虑的activity非正常退出，还原状态
if (savedInstanceState != null) {
mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);
}

// Inflate the layout for this fragment
return inflater.inflate(R.layout.article_view, container, false);
}

@Override
public void onStart() {
super.onStart();

// During startup, check if there are arguments passed to the fragment.
// onStart is a good place to do this because the layout has already been
// applied to the fragment at this point so we can safely call the method
// below that sets the article text.
Bundle args = getArguments();
if (args != null) {
// Set article based on argument passed in
updateArticleView(args.getInt(ARG_POSITION));
} else if (mCurrentPosition != -1) {
// Set article based on saved instance state defined during onCreateView
updateArticleView(mCurrentPosition);
}
}

public void updateArticleView(int position) {
TextView article = (TextView) getActivity().findViewById(R.id.article);
article.setText(Ipsum.Articles[position]);
mCurrentPosition = position;
}

@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);

// Save the current article selection in case we need to recreate the fragment
outState.putInt(ARG_POSITION, mCurrentPosition);
}
}

主activity，MainActivity.java

package com.hitsz.xiaokai.fragmentcom;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;

import com.hitsz.xiaokai.fragmentcom.ArticleFragment;
import com.hitsz.xiaokai.fragmentcom.R;
//实现需要通信Fragment的内部接口
public class MainActivity extends FragmentActivity
implements HeadlinesFragment.OnHeadlineSelectedListener {

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.news_articles);

// Check whether the activity is using the layout version with
// the fragment_container FrameLayout. If so, we must add the first fragment如果不是xml加载需要使用Fragment事务加载Fragment
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 an instance of ExampleFragment
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添加Fragment到activity的主要方法
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
}
}

public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment

// Capture the article fragment from the activity layout
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 {
// If the frag is not available, 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();
//通过bundle携带数据，传递数据给articleFragment，Fragment之间的通信方式
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 添加返回栈
transaction.replace(R.id.fragment_container, newFragment);
transaction.addToBackStack(null);

// Commit the transaction提交事务
transaction.commit();
}
}
}

运行效果：